Immunity can be defined as the body's ability to defend against specific pathogens and/or foreign substances in the initiation of disease processes. The multidimensional response initiated by the body's various defense systems is known as the immune response. Some of these responses become active almost immediately, while others develop slowly over time. It is the coordinated interaction of these mechanisms that allows the body to maintain normal internal homeostasis. However, when these mechanisms are either depressed or overactive, they become responsible for many of the pathophysiologic processes encountered in health care [1,2].

Passive immunity is immunity transferred from another source. The most common form is immunity conferred from mother to fetus. During fetal development, maternal immunoglobulin G (IgG) antibodies are transferred to the fetus via the placenta. After birth, the neonate also receives IgG antibodies from the mother in breast milk or colostrum. Therefore, infants are provided with some degree of protection from infection for approximately three to six months, giving their own immune system time to mature. Some protection against infectious diseases can also be provided by the administration of immunoglobulins pooled from human or animal sources. Passive immunity produces only short-term protection that lasts weeks to months [3].

Cytokines are low-molecular-weight, regulatory, pro- or anti-inflammatory proteins that are produced by cells of the innate and adaptive immune systems and that mediate many of the actions of these cells. The majority of the functionally important cytokines are interleukins, interferons, and tumor necrosis factor-alpha (TNF-α). Cytokines generate their responses by binding to specific receptors on their target cells and activating G-protein-coupled receptors [6,7].

Interleukins are produced by macrophages and lymphocytes in response to the presence of an invading micro-organism or activation of the inflammatory process. Their primary function is to enhance the acquired immune response through alteration of molecular expression, induction of leukocyte maturation, enhanced leukocyte chemotaxis, and general suppression or enhancement of the inflammatory process [1,6,7].

Interferons are cytokines that primarily protect the host against viral infections and play a role in the modulation of the inflammatory response. Interferons are cell-type specific, with IFN-α and IFN-β produced primarily by macrophages and IFN-γ produced primarily by T lymphocytes.

TNF-α, a cytokine in a class by itself, is one of the most important mediators of the inflammatory response and is produced by macrophages when surface toll-like receptors recognize pathogen-associated molecular patterns (PAMPs) on the surface of micro-organisms. TNF-α acts as an endogenous pyrogen (i.e., fever producer) and induces synthesis of preinflammatory substances in the liver. With prolonged exposure, it has the ability to cause intravascular coagulation and subsequent thrombosis production [1,6,7].

Despite the diverse functions of the cytokines, they all share certain important properties. All cytokines are secreted in a brief, self-limited manner. They are rarely stored as preformed molecules but rather are synthesized through transcription as a result of cellular activation. The actions of cytokines are often pleiotropic, meaning that a single cytokine has the ability to act on a variety of different cell types. For example, the interleukin IL-17 is produced by T-helper 17 (T17H) cells and acts on several cell types, including leukocytes, epithelial cells, mesothelial cells, vascular endothelial cells, and fibroblasts. As a result, T17H cells play a critical role in host defense against pathogens that infiltrate the mucosal barrier. Although pleiotropic action allows cytokines to mediate diverse effects, it greatly limits their use for therapeutic purposes. Because of this redundancy, antagonists against a single cytokine may not have functional consequences; other cytokines may compensate. Redundancy refers to the ability of different cytokines to stimulate the same or overlapping biologic functions [1,6,7].

As noted, chemokines are small-protein molecules (consisting of 70 to 130 amino acids) that are involved in immune and inflammatory cellular responses and function to control the migration of leukocytes to their primary site of action in the immune response. There are four distinct classes of chemokines (C, CC, CXC, and CX3C), each named for the number and location of cysteine residing on the terminal amino acid of the protein. Currently, 47 distinct chemokine molecules have been identified within the four different classes. The vast majority of these are classified as either CC or CXC chemokines. The CC chemokines have the first two cysteine molecules adjacent to each other, while these molecules are separated by an amino acid in the CXC chemokines. The CC chemokines attract monocytes, lymphocytes, and eosinophils to sites of chronic inflammation. The CXC chemokines attract neutrophils to sites of acute inflammation [8,9].

Invading pathogens contain conserved structures in their cell membranes termed PAMPs, which are recognized by the cells of the innate immune system because they possess a limited number of germline-encoded pattern-recognition receptors (PRRs). Upon PAMP recognition, PRRs come in contact with the cell surface and/or send intracellular signals to the host that trigger proinflammatory and antimicrobial responses, including the synthesis and release of cytokines, chemokines, and cell-adhesion molecules. The PAMPs recognized by host PRRs are made up of a combination of sugars, lipid molecules, proteins, and/or patterns of modified nucleic acids. Because PAMPs are essential for the functioning and infectivity of the micro-organism, mutation cannot help it avoid immune recognition. The human complement of PRRs is extensive (approximately 1,000), so the classes of pathogens recognized are diverse. Pathogens of very different biochemical composition are recognized by relatively similar mechanisms by host PRRs, and no single class of pathogens is sensed by only one type of PRR; the host genetic code allows for the unique receptors involved in both innate and adaptive immunity to recognize fine details of molecular structure [3].

The innate immune system is comprised of two separate but inter-related lines of defense: the epithelial layer, which acts as a physical barrier to invading substances and organisms, and the inflammatory response. The innate immune response utilizes the body's natural epithelial barriers along with phagocytic cells (mainly neutrophils and macrophages), natural killer (NK) cells, and several plasma proteins, including kinins, clotting factors, and those of the complement system, to maintain internal homeostasis. The response of the innate immune system is rapid, usually within minutes to hours, and prevents the establishment of infection and deeper tissue penetration of micro-organisms. The innate immune response is effective against most pathogens. However, when the innate response is overwhelmed or ineffective, adaptive immune responses become activated as the final line of defense against invading organisms. Innate immune mechanisms are always present in the body and are rapidly activated, so the body's defenses have responded before the adaptive immune response is triggered. The innate immune system also interacts with and directs adaptive immune responses [9,10].

The leukocytes (white blood cells) involved in the innate immune response are derived from myeloid stem cells and subdivided into two distinct groups based on the presence or absence of specific staining granules in their cytoplasm. Leukocytes that contain granules are classified as granulocytes and include neutrophils, eosinophils, and basophils. Cells that lack granules are classified as lymphocytes or monocytes [4].

Monocytes are the largest in size of all the white blood cells but make up only 3% to 7% of the total leukocyte count. They are released from the bone marrow into the bloodstream, where they migrate into tissues and mature into macrophages and dendritic cells. These cells participate in the inflammatory response and phagocytize foreign substances and cellular debris. Macrophages have a long life span, reside in the tissues, and are the first phagocyte that invading organisms encounter upon entering the body. Neutrophils and macrophages work in concert with each other and are crucial to the host's defense against all intracellular and extracellular pathogens [4].

Dendritic cells are specialized, bone marrow-derived leukocytes found in lymphoid tissue and are the bridge between the innate and adaptive immune systems. These cells take their name from the dendrites within the central nervous system (CNS), because they have surface projections that give them a similar appearance. Dendritic cells are relatively rare and are found mainly in tissues exposed to external environments, such as the respiratory and gastrointestinal systems. They are present primarily in an immature form that is available to directly sense pathogens, capture foreign agents, and transport them to secondary lymphoid tissues. Once activated, dendritic cells undergo a complex maturation process in order to function as key antigen-presenting cells capable of initiating adaptive immunity. As noted, dendritic cells are responsible for the processing and presenting of foreign antigens to the lymphocytes and, like macrophages, also release several communication molecules that direct the nature of adaptive immune responses [4,5].

Lymphocytes make up approximately 36% of the total white cell count and are the primary cells of the adaptive immune response. They arise from stem cells in bone marrow. B lymphocytes are responsible for forming the antibodies that provide humoral immunity, whereas T lymphocytes provide cell-mediated immunity. T and B lymphocytes are unique in that they are the only cells in the body capable of using cellular "memory" to assess the surfaces of microbial agents and other pathogens to recognize specific pathogens. These processes make the adaptive immune processes organism-specific [5]. Many autoimmune diseases, such as Hashimoto thyroiditis and type 1 diabetes, are caused by impairment in both B and T lymphocyte (specifically cytotoxic lymphocyte) functions, resulting in direct cellular damage because the body's immune system is no longer capable of distinguishing "self" from "non-self" [4].

The class I and II MHC genes are responsible for encoding human leukocyte antigens (HLAs), which are proteins bound on cell surfaces that define the individual's tissue type. These molecules are present on cell-surface glycoproteins that form the basis for human tissue typing. Each individual has a unique collection of MHC proteins representing a unique set of polymorphisms. MHC polymorphism affects immune responses as well as susceptibility to a number of diseases. Because of the number of MHC genes and the possibility of several alleles for each gene, it is almost impossible for any two individuals to have an identical MHC profile [13].

The central and peripheral lymphoid organs are responsible for the production, maturation, and storage of large numbers of immune system cells, including the B and T lymphocytes. These organs and tissues are widely distributed throughout the body and provide different, but often overlapping, functions. The central lymphoid organs are comprised of the bone marrow and the thymus and are responsible for immune cell production and maturation. The tissues and cells of the peripheral lymph node system store the cells of the immune system, where they function to concentrate and process antigens as well as support cellular processes necessary for the development of fully functioning adaptive immune responses. These peripheral lymphoid tissues are comprised of the lymph nodes, spleen, tonsils, appendix, Peyer patches in the intestine, and mucosa-associated lymphoid tissues in the respiratory, gastrointestinal, and reproductive systems. Networks of lymph channels, blood vessels, and capillaries connect the lymphoid organs and transport immune cells, antigens, and cellular debris throughout the body [7].

Neonates are protected against antigens in early life as result of passive transfer of maternal IgG antibodies through the placenta and IgA antibodies in colostrum. Maternal IgG antibodies readily cross the placenta during fetal development and remain functional in the newborn for the first few months of life, providing passive immunity until immunoglobulin production is well established in the newborn. IgG is the only class of immunoglobulins able to cross the placenta. Maternally transmitted IgG is effective against most micro-organisms and viruses that a neonate encounters. The largest amount of IgG crosses the placenta during the last weeks of pregnancy and is stored in fetal tissues. Infants born prematurely may be deficient in maternal antibodies and, therefore, more susceptible to infections. Because of transfer of IgG antibodies to the fetus, an infant born to a mother infected with human immunodeficiency virus (HIV) has a positive HIV antibody test result, although the child may not be infected with the virus [3].

As people age, the ability of the immune system to protect the body from pathogenic organisms and environmental toxins declines in relation to an overall decline in both cell-mediated and humoral immune responses. Therefore, older adults are more susceptible to infections, have more evidence of autoimmune and immune complex disorders, and have a higher incidence of cancer than younger people. In addition, the immune system of older adults is less likely to respond appropriately to immunization, resulting in a weakened response to vaccination. Older adults also frequently have comorbid conditions that impair normal immune function and compromise the immune response [10].

The genetic predisposition to develop allergies that involve IgE antibody formation is known as atopy. The terms atopic, allergic, and hypersensitive are frequently used interchangeably. Allergy (or, more appropriately, hypersensitivity) describes the increased immune response to the presence of an antigen. Between 20% and 30% of the population have allergies. Although it is not possible to predict who will have allergies, there is a higher incidence of allergies among children of parents with allergies [11,15].

Examples of type 1 hypersensitivity reactions include anaphylaxis, allergic rhinitis, asthma, and acute allergic drug reactions [19]. The immediate (antigen-antibody) reaction occurs within minutes after exposure to the allergen. The resultant IgE production induces the immediate response by activating mast cells and basophils, causing them to degranulate and release mediators such as histamine, leukotrienes from basophils and prostaglandins, and platelet-activating factors from eosinophils. The mediators, whether preformed or formed after activation, are able to increase vascular permeability, dilate vessels, contract smooth muscle, and ignite other inflammatory cells [18].

With intradermal or injection skin testing, the healthcare practitioner introduces a small quantity of allergen into the skin by quickly pricking, scratching, or puncturing it or by using intradermal injections. A wheal and flare reaction usually occurs soon after the allergen is introduced if the patient is allergic. This type of skin testing is the most accurate, but it is linked to a higher incidence of severe allergic reactions. Therefore, it should be used with caution and under close supervision. A patch test can be used to evaluate contact allergies; the allergen is applied directly to the skin and then covered with a gauze dressing [25]. Skin testing is generally considered safe, but it always carries a risk of causing a systemic reaction such as anaphylaxis [25].

Pulmonary function tests calculate the amount and rate of air expelled during a single breath, helping to discern whether constricted airways are responsible for blocked airflow [16]. Guidelines for normal breathing are based on analysis of data obtained from large segments of the population. A patient's information is plotted on a continuum, allowing comparison to average breathing patterns for healthy individuals of the same sex, age, and size. Two common methods of measuring airflow assess forced expiratory volume (FEV1) and peak expiratory flow (PEF) [16,26].

A spirometer is a simple machine used to determine both the total amount of air that can be forcefully exhaled after maximum inspiration, referred to as forced vital capacity (FVC), and how fully air can be expelled from the lungs, measured by the amount of air forced from the lungs in one second, which is expressed as FEV1[16,26]. The spirometer is generally used in diagnosis to establish airflow obstruction and reversibility [27]. Obstruction may be ascertained if the FEV1 is less than 80% of the predicted value or if FEV1 divided by FVC is less than 65%. Normally, the FEV1 should account for more than 75% of the FVC; anything less than 75% indicates a possible obstruction and 65% or less may indicate a diagnosis of asthma [27].

A peak flow meter measures the speed of exhalation. The highest speed or best flow is PEF or peak flow. The peak flow meter is less sophisticated than a spirometer, which provides a more thorough assessment of lung function. However, the meter has the advantages of being less expensive, portable, and easy to use [26]. The severity of a patient's asthma can be determined by careful and consistent monitoring of peak flow and comparison of a patient's best peak flow to standard measurements. Studies confirm that short-term peak flow measurements assist healthcare providers in assessing asthma severity [16].

Studies have shown that measuring exhaled nitric oxide is also helpful in evaluating and diagnosing asthma [27]. Nitric oxide is a mediator for the inflammation that occurs during an asthma episode; the amount of nitric oxide measured during exhalation will directly correlate with the inflammation in the bronchial tubes [28].

Manifestations of allergic rhinitis are persistent and show seasonal variation. Nasal manifestations are often accompanied by eye irritation, which causes pruritus, erythema, and excessive tearing. Numerous allergens may cause these manifestations, including tree pollens (spring), grasses (summer), ragweed (fall), or dust mites and animal dander (year-round) [17].

Early recognition of the clinical signs and symptoms of anaphylaxis is necessary to ensure immediate, appropriate treatment. In most cases, these signs and symptoms will occur within one hour after the accidental exposure (ranging from less than one minute to a few hours) and will vary in terms of presence, sequence, and severity [41]. In 1% to 20% of anaphylaxis cases, there will be a biphasic response, with recurrence of symptoms 8 to 12 hours later, after the individual had seemed to recover [41]. The interval between the initial reaction and the recurrence has ranged from 1 to 72 hours [38,42]. A biphasic reaction occurs in approximately 6% to 11% of children; such reactions typically occur within 8 hours after the first reaction but may occur as long as 72 hours later [43].

As with less severe allergic reactions, cutaneous manifestations are the most common, followed by respiratory and gastrointestinal symptoms [42,44,45,46]. In one study of more than 600 children, cutaneous manifestations were documented in 87% to 98% of children; respiratory manifestations, in 59% to 81%; and gastrointestinal manifestations, in 50% to 59% [46]. The cardiovascular system is less frequently involved and is more often involved in adolescents [43,46]. Still, cutaneous manifestations may be absent in about 10% to 20% of cases of anaphylaxis, which may contribute to under-recognition [44].

Food allergy manifests itself primarily through the skin, gastrointestinal tract, and respiratory system, and symptoms are categorized as acute or delayed (Table 2) [44]. Cutaneous symptoms are typically the most common.

Asthma has many puzzling aspects, and its symptoms may wax and wane, especially seasonally [16]. Unlike other respiratory diseases, such as COPD and emphysema, in which air trapping and hyperinflation of the lungs also occur, asthma is reversible with the use of proper medications and therapies.

Anti-inflammatory medications block production of substances from cells involved in inflammation, such as mast cells; this action reduces or reverses the swelling that causes asthma symptoms [16]. Equally important, these medications lessen airway sensitivity, which prevents edema [16]. If asthma symptoms appear more than once or twice per week and less powerful options cannot control them, anti-inflammatory medication is indicated [16]. Before newer drugs were developed, the only anti-inflammatory asthma medication available was an oral corticosteroid, such as prednisone. Long-term treatment with oral corticosteroids is associated with serious side effects, including stunted growth in children, hyperlipidemia, thinning skin, and immune system impairment, making patient compliance difficult. As a result, several inhaled anti-inflammatory drugs were developed, which greatly reduced negative reactions [16]. The four primary types of anti-inflammatory drugs are corticosteroids, mast cell stabilizers, antiallergic medications, and antileukotriene medications [16].

An estimated 1.5 million American adults are affected by rheumatoid arthritis [84]. The yearly incidence of rheumatoid arthritis is approximately 53 per 100,000 for women and about half that (27.7 per 100,000) for men [84]. These figures vary significantly based on the age of the cohort. The data show that the incidence of rheumatoid arthritis increases steadily with age in both sexes, until approximately 65 to 74 years of age, when incidence peaks [84]. However, women in all age groups have a much higher incidence compared with men.

Findings on general physical examination of the patient with rheumatoid arthritis are normal except for an occasional low-grade fever (38°C) and a slightly elevated pulse rate. The characteristic patient initially presents with complaints of pain and stiffness in multiple joints. There is prominent and prolonged morning stiffness (lasting more than one hour) that usually begins gradually with fatigue, loss of appetite, widespread muscle aches, and weakness [86,89,90].

Today, the recommended standard of treatment is a tightly controlled, aggressive strategy tailored to each patient, with modifications to the individual medication regimen to achieve a particular target (remission, or alternatively, low disease activity) in a specific period of time (usually six months) [91,93]. The "treat-to-target" approach for a patient with early high disease activity and poor prognostic features typically involves initiation of methotrexate and/or another DMARD(s) immediately upon diagnosis [91,92,93]. Initial combination therapies with DMARDs, particularly those including a biologic anti-TNF agent, appear to provide earlier clinical improvement and less joint damage progression in patients with early moderate or highly active disease; they can be withdrawn successfully, and fewer treatment adjustments are needed than with initial monotherapies [91,93,94,95,96]. Patients with active disease are monitored closely (every one to three months), and it is recommended that treatment adjustments be made if there is no improvement at three months (or if the six-month target has not been reached) [91,93]. Patients with low-to-moderate disease activity or high disease activity without poor prognostic features are typically started on DMARD monotherapy. NSAIDs, glucocorticoids, or cyclooxygenase-2 (COX-2) inhibitors are often used concurrently to treat rheumatoid arthritis-associated joint pain and inflammation. However, they do not alter the disease course and should not be used as single therapy.

A shortage or functional failure of T lymphocytes is believed to be partially responsible for this autoimmune reaction. Red blood cells, neutrophils, platelets, lymphocytes, or almost any organ or tissue in the body may be attacked. One of the hallmark indicators of lupus is the formation of autoantibodies, and the presence of autoantibodies in the blood is a key factor to the diagnosis of lupus [100,101,104].

Common symptoms of lupus include fever, weight loss, malaise, fatigue, skin rashes, polyarthralgia, vasculitis, Raynaud syndrome, patchy alopecia (hair loss), and painless ulcers of the mucous membranes [104]. Fatigue is probably the most universal symptom, described as a persistent complaint of a paralyzing fatigue that normal rest may not relieve [100]. Vague symptoms of lupus include aching, fatigue, low-grade or spiking fever, chills, and malaise. Episodic fever is reported by more than 80% of all patients with lupus, with a low-grade fever most often noted [100]. Infection is certainly a major concern and is a potential symptom for patients with lupus. Those with lupus are more susceptible to opportunistic infections due to alterations in their hematologic system, especially in white blood cells. Women with lupus may also experience irregular periods or amenorrhea due to the disease process [100,101].

The diagnosis of lupus can be facilitated with a physical examination, extensive patient history, various laboratory tests, and radiographic evaluations [101,104]. There are several laboratory procedures that help to diagnose and monitor individuals with lupus; these various tests have different implications for the patient, but the antinuclear antibody (ANA) test is the most specific and sensitive test for lupus and is therefore the most commonly used autoantibody test. Ninety-seven percent of patients with lupus have a positive ANA blood test. The titer and patterns of the blood sample are reported. A titer greater than 1:80 is usually considered positive [106]. It is important to note that a positive ANA test is found in 97% of patients with lupus, but alone, it does not indicate a conclusive diagnosis of lupus [106]. A positive ANA test, although not always found, satisfies one of the four typical clinical characterizations required for a definitive diagnosis of lupus. ANA tests may also be positive in patients with other connective tissue diseases, chronic infectious diseases, and autoimmune diseases [106].

Among the most common manifestations of extraglandular involvement are joint pain and/or swelling (37% to 75%), gastrointestinal symptoms (54%), pulmonary disease (e.g., chronic cough, recurrent bronchitis, fibrosis) (29%), and Raynaud phenomenon (16% to 28%) [112,113]. Occurring less frequently are cutaneous vasculitis, lymphadenopathy, and renal involvement (e.g., proteinuria, interstitial nephritis, glomerulonephritis) [112,113]. Peripheral neuropathies are often associated with Sjögren syndrome, and the reported prevalence of this complication has ranged widely, from 10% to more than 60% [114,115]. Cognitive dysfunction has been reported in about half of individuals [114].

Literally, ankylosing spondylitis refers to fusion (ankylosis) of inflamed vertebrae (spondylitis). The disease typically begins in the spine of young men in their late teens or early twenties. The average annual age-adjusted incidence of ankylosing spondylitis has been reported to be 6.6 per 100,000 population, with men being affected three times as frequently as women. Although the usual age of onset is set between 15 and 35 years, the age group with the highest incidence is those 25 to 34 years of age [24].

Inflammatory diseases of muscle are a heterogeneous group of disorders characterized by proximal muscle weakness and nonsuppurative inflammation of skeletal muscle. The idiopathic myopathies are categorized more specifically as polymyositis (affecting both sides of the body), dermatomyositis (characterized by a distinctive rash), inclusion body myositis (the most common form in older adults), and necrotizing autoimmune myopathy. As a group, these are relatively rare diseases, and accurate estimates of their prevalence are difficult to obtain. Muscle weakness with an underlying malignancy develops in a subset of patients with inflammatory myopathies. Malignancy may precede or follow the onset of muscle weakness.

On exam, the affected scalp artery is sometimes prominent. It may be tender and is often pulseless. The scalp itself is usually tender as well. Depending upon the progression, visual field defects and decreased acuity may be noted, although the patient does not usually exhibit focal neurologic deficits. Typically, the headache occurs in someone who is febrile, has malaise, and feels aches in the back and shoulders. Claudication of the jaw occurs commonly and is virtually pathognomonic for this condition when present during talking or chewing [127].

Stage 3 (late disseminated stage) is the chronic phase, which may appear months to years after the initial infection [129]. Various names for this stage have been proposed and are currently used, including post-Lyme syndrome, post-Lyme disease syndrome, post-treatment chronic Lyme disease, or chronic Lyme disease [137]. One of the most common findings in this stage is oligoarthritis, with the knee being the most frequently affected joint, although other joints can become inflamed [129,136]. Pain is usually out of proportion to the swelling [129]. Musculoskeletal pain, spinal radiculopathy with paresthesias, encephalopathy, and the symptom complex of fibromyalgia or chronic fatigue syndrome may be present. This stage is associated with chronic borreliosis; consequently, cardiac arrhythmias, respiratory compromise, and spread to the entire nervous system are liable to occur. It is suspected that fibromyalgia may be a long-term sequela to chronic Lyme disease. If untreated, chronic expression results in potentially crippling arthritic changes as well as organ system involvement. The organism can establish itself in the bladder wall and reoccur with another exposure or stress from another illness [133].

Prompt and complete treatment with antibiotics is important to prevent the development of chronic Lyme disease and/or chronic neuroborreliosis and their troublesome sequelae. The International Lyme and Associated Diseases Society (ILADS) suggests that Lyme disease should be treated with doxycycline as the antibiotic of choice for prophylaxis following an Ixodes tick bite with known feeding, irrespective of the amount of tick engorgement or the local tick population infection rate [139]. Where doxycycline is contraindicated, antibiotics known to be effective for treating Lyme disease, such as amoxicillin, azithromycin, or cefuroxime, may be substituted. The recommended adult dose and prophylactic regimen is 100–200 mg doxycycline twice daily for 20 days [139].

The clinical manifestations of HIV disease are determined by the stage of primary infection and the chronicity and degree of the resultant cellular immunodeficiency state. Acute, primary HIV infection may be asymptomatic, but most often it is manifest by a subacute viral syndrome of malaise and fatigue, fever, sore throat, rash, myalgia, headache, and lymphadenopathy—clinical features similar in many respects to that seen with Epstein-Barr virus mononucleosis, CMV, and certain types of herpes simplex infections [145]. A variety of atypical symptoms and signs may be seen, including aseptic meningitis syndrome, genital ulcers, and ulcerations involving the gingiva, palate, or buccal mucosa. The acute illness usually resolves in less than 14 days but may follow a protracted course over many weeks [145].

For treatment-naïve patients, initial recommended therapy generally consists of two NRTIs in combination with a third active antiretroviral drug from one of three drug classes: an INSTI, an NNRTI, or a PI with a pharmacokinetic enhancer (cobicistat or ritonavir) [146]. These regimens result in maximum reduction of viral load for the longest period of time. When used as initial therapy, these regimens will achieve the goal of no detectable virus in the majority of patients after four to six months [146].

Because there are many PIDDs, treatment options are targeted toward the specific immune defects [154]. Options include transplantation (e.g., bone marrow, stem cell, thymus), immunoglobulin replacement, preventive antibiotics, strategies to manage autoimmune disease, and in some cases, gene therapy.

The Hour-1 Bundle consists of five elements that are intended to be initiated within the first hour after the time of triage in the emergency department or, if referred from another care location, from the earliest chart annotation consistent with all elements of sepsis or septic shock. The five elements are [80]: