Markers Involved in Innate Immunity and Neutrophil Activation are Elevated during Acute Human Anaphylaxis: Validation of a Microarray Study.

BACKGROUND: We have previously identified the upregulation of the innate immune response, neutrophil activation, and apoptosis during anaphylaxis using a microarray approach. This study aimed to validate the differential gene expression and investigate protein concentrations of "hub genes" and upstream regulators during anaphylaxis. METHODS: Samples were collected from patients with anaphylaxis on their arrival at the emergency department, and after 1 and 3 h. mRNA levels of 11 genes (interleukin-6 [IL-6], IL-10, oncostatin M [OSM], S100A8, S100A9, matrix metalloproteinase 9 [MMP9], FASL, toll-like receptor 4 [TLR4], MYD88, triggering receptor expressed on myeloid cells 1 [TREM1], and cluster of differentiation 64 [CD64]) were measured in peripheral blood leucocytes using qPCR. Serum protein concentrations were measured by ELISA or cytometric bead array for 6 of these candidates. RESULTS: Of 69 anaphylaxis patients enrolled, 36 (52%) had severe reactions, and 38 (55%) were female. Increases in both mRNA and protein of IL-10, S100A9, MMP9, and TREM1 were observed. OSM, S100A8, TLR4, and CD64 were upregulated and IL-6 protein concentrations were increased during anaphylaxis. Both FASL and soluble Fas ligand decreased during anaphylaxis. CONCLUSION: These results provide evidence for the involvement of innate immune pathways and myeloid cells during human anaphylaxis, validating previous microarray findings. Elevated S100A8, S100A9, TLR4, and TREM1 expression, and increased S100A9 and soluble TREM1 protein concentrations strongly suggest that neutrophils are activated during acute anaphylaxis.

Changes in differential gene expression during a fatal stroke.

We present a young woman (with an identical twin sister) who arrived at the Emergency Department (ED) within 1 hour of her initial stroke symptoms. Previous microarray studies have demonstrated differential expression of multiple genes between stroke patients and healthy controls. However, for many of these studies there is a significant delay between the initial symptoms and collection of blood samples, potentially leaving the important early activators/regulators of the inflammatory response unrecognised. Blood samples were collected from the patient for an analysis of differential gene expression over time during the evolution of a fatal stroke. The time points for blood collection were ED arrival (T0) and 1, 3 and 24 hours post ED arrival (T1, T3 and T24). This was compared to her identical twin and an additional two age and sex-matched healthy controls. When compared to the controls, the patient had 12 mRNA that were significantly upregulated at T0, and no downregulated mRNA (with a cut off fold change value ±1.5). Of the 12 upregulated mRNA at T0, granzyme B demonstrated the most marked upregulation on arrival, with expression steadily declining over time, whereas S100 calcium-binding protein A12 (S100A12) gene expression increased from T0 to T24, remaining >two-fold above that in the healthy controls at T24. Other genes, such as matrix metalloproteinase 9, high mobility group box 2 and interleukin-18 receptor I were not upregulated at T0, but they demonstrated clear upregulation from T1­T3, with gene expression declining by T24. A greater understanding of the underlying immunopathological mechanisms that are involved during the evolution of ischaemic stroke may help to distinguish between patients with stroke and stroke mimics.

Changes in differential gene expression during a fatal stroke.

We present a young woman (with an identical twin sister) who arrived at the Emergency Department (ED) within 1hour of her initial stroke symptoms. Previous microarray studies have demonstrated differential expression of multiple genes between stroke patients and healthy controls. However, for many of these studies there is a significant delay between the initial symptoms and collection of blood samples, potentially leaving the important early activators/regulators of the inflammatory response unrecognised. Blood samples were collected from the patient for an analysis of differential gene expression over time during the evolution of a fatal stroke. The time points for blood collection were ED arrival (T0) and 1, 3 and 24hours post ED arrival (T1, T3 and T24). This was compared to her identical twin and an additional two age and sex-matched healthy controls. When compared to the controls, the patient had 12 mRNA that were significantly upregulated at T0, and no downregulated mRNA (with a cut off fold change value ±1.5). Of the 12 upregulated mRNA at T0, granzyme B demonstrated the most marked upregulation on arrival, with expression steadily declining over time, whereas S100 calcium-binding protein A12 (S100A12) gene expression increased from T0 to T24, remaining >two-fold above that in the healthy controls at T24. Other genes, such as matrix metalloproteinase 9, high mobility group box 2 and interleukin-18 receptor I were not upregulated at T0, but they demonstrated clear upregulation from T1-T3, with gene expression declining by T24. A greater understanding of the underlying immunopathological mechanisms that are involved during the evolution of ischaemic stroke may help to distinguish between patients with stroke and stroke mimics.

Sustained elevation of resistin, NGAL and IL-8 are associated with severe sepsis/septic shock in the emergency department.

OBJECTIVE: To identify biomarkers which distinguish severe sepsis/septic shock from uncomplicated sepsis in the Emergency Department (ED). METHODS: Patients with sepsis underwent serial blood sampling, including arrival in the ED and up to three subsequent time points over the first 24 hours. Messenger RNA (mRNA) levels of 13 genes representing arms of the innate immune response, organ dysfunction or shock were measured in peripheral blood leucocytes using quantitative PCR, and compared with healthy controls. Serum protein concentrations of targets differentially expressed between uncomplicated sepsis and severe sepsis/septic shock were then measured at each time point and compared between the two patient groups. RESULTS: Of 27 participants (median age 66 years, (IQR 35, 78)), 10 had uncomplicated sepsis and 17 had sepsis with organ failure (14 septic shock; 3 had other sepsis-related organ failures). At the time of first sample collection in the ED, gene expression of Interleukin (IL)-10 and Neutrophil Gelatinase Associated Lipocalin (NGAL) were significantly higher in severe sepsis than uncomplicated sepsis. Expression did not significantly change over time for any target gene. Serum concentrations of IL-6, IL-8, IL-10, NGAL and Resistin were significantly higher in severe sepsis than uncomplicated sepsis at the time of first sample collection in the ED, but only IL-8, NGAL and Resistin were consistently higher in severe sepsis compared to uncomplicated sepsis at all time points up to 24 h after presentation. CONCLUSIONS: These mediators, produced by both damaged tissues and circulating leukocytes, may have important roles in the development of severe sepsis. Further work will determine whether they have any value, in addition to clinical risk parameters, for the early identification of patients that will subsequently deteriorate and/or have a higher risk of death.

Genomic responses during acute human anaphylaxis are characterized by upregulation of innate inflammatory gene networks.

BACKGROUND: Systemic spread of immune activation and mediator release is required for the development of anaphylaxis in humans. We hypothesized that peripheral blood leukocyte (PBL) activation plays a key role. OBJECTIVE: To characterize PBL genomic responses during acute anaphylaxis. METHODS: PBL samples were collected at three timepoints from six patients presenting to the Emergency Department (ED) with acute anaphylaxis and six healthy controls. Gene expression patterns were profiled on microarrays, differentially expressed genes were identified, and network analysis was employed to explore underlying mechanisms. RESULTS: Patients presented with moderately severe anaphylaxis after oral aspirin (2), peanut (2), bee sting (1) and unknown cause (1). Two genes were differentially expressed in patients compared to controls at ED arrival, 67 genes at 1 hour post-arrival and 2,801 genes at 3 hours post-arrival. Network analysis demonstrated that three inflammatory modules were upregulated during anaphylaxis. Notably, these modules contained multiple hub genes, which are known to play a central role in the regulation of innate inflammatory responses. Bioinformatics analyses showed that the data were enriched for LPS-like and TNF activation signatures. CONCLUSION: PBL genomic responses during human anaphylaxis are characterized by dynamic expression of innate inflammatory modules. Upregulation of these modules was observed in patients with different reaction triggers. Our findings indicate a role for innate immune pathways in the pathogenesis of human anaphylaxis, and the hub genes identified in this study represent logical candidates for follow-up studies.

Immediate-type hypersensitivity drug reactions.

Hypersensitivity reactions including anaphylaxis have been reported for nearly all classes of therapeutic reagents and these reactions can occur within minutes to hours of exposure. These reactions are unpredictable, not directly related to dose or the pharmacological action of the drug and have a relatively high mortality risk. This review will focus on the clinical presentation, immune mechanisms, diagnosis and prevention of the most serious form of immediate onset drug hypersensitivity reaction, anaphylaxis. The incidence of drug-induced anaphylaxis deaths appears to be increasing and our understanding of the multiple and complex reasons for the unpredictable nature of anaphylaxis to drugs is also expanding. This review highlights the importance of enhancing our understanding of the biology of the patient (i.e. immune response, genetics) as well as the pharmacology and chemistry of the drug when investigating, diagnosing and treating drug hypersensitivity. Misdiagnosis of drug hypersensitivity leads to substantial patient risk and cost. Although oral provocation is often considered the gold standard of diagnosis, it can pose a potential risk to the patient. There is an urgent need to improve and standardize diagnostic testing and desensitization protocols as other diagnostic tests currently available for assessment of immediate drug allergy are not highly predictive.

Immune response to snake envenoming and treatment with antivenom; complement activation, cytokine production and mast cell degranulation.

BACKGROUND: Snake bite is one of the most neglected public health issues in poor rural communities worldwide. In addition to the clinical effects of envenoming, treatment with antivenom frequently causes serious adverse reactions, including hypersensitivity reactions (including anaphylaxis) and pyrogenic reactions. We aimed to investigate the immune responses to Sri Lankan snake envenoming (predominantly by Russell's viper) and antivenom treatment. METHODOLOGY/PRINCIPAL FINDINGS: Plasma concentrations of Interleukin (IL)-6, IL-10, tumor necrosis factor α (TNFα), soluble TNF receptor I (sTNFRI), anaphylatoxins (C3a, C4a, C5a; markers of complement activation), mast cell tryptase (MCT), and histamine were measured in 120 Sri Lankan snakebite victims, both before and after treatment with antivenom. Immune mediator concentrations were correlated with envenoming features and the severity of antivenom-induced reactions including anaphylaxis. Envenoming was associated with complement activation and increased cytokine concentrations prior to antivenom administration, which correlated with non-specific systemic symptoms of envenoming but not with coagulopathy or neurotoxicity. Typical hypersensitivity reactions to antivenom occurred in 77/120 patients (64%), satisfying criteria for a diagnosis of anaphylaxis in 57/120 (48%). Pyrogenic reactions were observed in 32/120 patients (27%). All patients had further elevations in cytokine concentrations, but not complement activation, after the administration of antivenom, whether a reaction was noted to occur or not. Patients with anaphylaxis had significantly elevated concentrations of MCT and histamine. CONCLUSIONS/SIGNIFICANCE: We have demonstrated that Sri Lankan snake envenoming is characterized by significant complement activation and release of inflammatory mediators. Antivenom treatment further enhances the release of inflammatory mediators in all patients, with anaphylactic reactions characterised by high levels of mast cell degranulation but not further complement activation. Anaphylaxis is probably triggered by non allergen-specific activation of mast cells and may be related to the quality of available antivenom preparations, as well as a priming effect from the immune response to the venom itself.

Anaphylaxis: clinical patterns, mediator release, and severity.

BACKGROUND: Prospective human studies of anaphylaxis and its mechanisms have been limited, with few severe cases or examining only 1 or 2 mediators. OBJECTIVES: We wanted to define the clinical patterns of anaphylaxis and relationships between mediators and severity. METHODS: Data were collected during treatment and before discharge. Serial blood samples were taken for assays of mast cell tryptase, histamine, anaphylatoxins (C3a, C4a, C5a), cytokines (IL-2, IL-6, IL-10), soluble tumor necrosis factor receptor I, and platelet activating factor acetyl hydrolase. Principal component analysis defined mediator patterns, and logistic regression identified risk factors and mediator patterns associated with reaction severity and delayed reactions. RESULTS: Of 412 reactions in 402 people, 315 met the definition for anaphylaxis by the National Institute of Allergy and Infectious Diseases/Food Allergy and Anaphylaxis Network. Of 97 severe reactions 45 (46%) were hypotensive, 23 (24%) were hypoxemic, and 29 (30%) were mixed. One patient died. Severe reactions were associated with older age, pre-existing lung disease, and drug causation. Delayed deteriorations treated with epinephrine occurred in 29 of 315 anaphylaxis cases (9.2%) and were more common after hypotensive reactions and with pre-existing lung disease. Twenty-two of the 29 delayed deteriorations (76%) occurred within 4 hours of initial epinephrine treatment. Of the remaining 7 cases, 2 were severe and occurred after initially severe reactions, within 10 hours. All mediators were associated with severity, and 1 group (mast cell tryptase, histamine, IL-6, IL-10, and tumor necrosis factor receptor I) was also associated with delayed deteriorations. Low platelet activating factor acetyl hydrolase activity was associated with severe reactions. CONCLUSION: The results suggest that multiple inflammatory pathways drive reaction severity and support recommendations for safe observation periods after initial treatment.

Ultrarush versus semirush initiation of insect venom immunotherapy: a randomized controlled trial.

BACKGROUND: Venom immunotherapy can be initiated by different schedules, but randomized comparisons have not been performed. OBJECTIVE: We aimed to compare the safety of 2 initiation schedules. METHODS: Patients of any age with prior immediate generalized reactions to jack jumper ant (Myrmecia pilosula) stings were randomized to venom immunotherapy initiation by a semirush schedule over 10 visits (9 weeks) or an ultrarush schedule over 3 visits (2 weeks). In a concurrent treatment efficacy study, the target maintenance dose was randomized to either 50 µg or 100 µg. The primary outcome was the occurrence of 1 or more objective systemic reactions during venom immunotherapy initiation. Analyses were by intention to treat. We also assessed outcomes in patients who declined randomization. RESULTS: Of 213 eligible patients, 93 were randomized to semirush (44 patients) or ultrarush (49 patients) initiation. Objective systemic reactions were more likely during ultrarush initiation (65% vs 29%; P < .001), as were severe reactions (12% vs 0%; P= .029). Times to maximal increases in venom-specific IgG(4) were no different between treatments, whereas the maximal increase in venom-specific IgE occurred earlier with ultrarush treatment. Similar differences between methods were observed in patients who declined randomization. One hundred seventy-eight patients were randomized to maintenance doses of either 50 µg (90 patients) or 100 µg (88 patients). The target maintenance dose had no effect on the primary outcome, but multiple-failure-per-subject analysis found that the 50 µg dose reduced the likelihood of reactions. CONCLUSION: Ultrarush initiation increases the risk of systemic reactions. A lower maintenance dose reduces the risk of repeated reactions, but the effect on treatment efficacy is unknown.

Mediators released during human anaphylaxis.

A range of mediators are generated during anaphylaxis, with redundancy of effects, multiple overlapping pathways, and involvement of several cell types. Key steps in the reaction occur at the site of initial contact, and mediators may not be detectable systemically. Furthermore, the potencies of various mediators vary enormously, and clinical effects may occur below our level of detection. We also do not know what converts (amplifies) a local reaction into systemic anaphylaxis. Murine models have identified several novel mediators that may propagate and/or regulate this process and also indicate that circulating neutrophils may play an important role in reaction amplification. Differential expression of various genes within specific intracellular signalling pathways of mediator release may further explain the varying severities of anaphylactic reactions. As our knowledge of the mechanisms of activation, key mediators, and the regulation of mediator release improves, new treatments for prevention and acute management may emerge.

Using time-resolved fluorescence to measure serum venom-specific IgE and IgG.

We adapted DELFIA™ (dissociation-enhanced lanthanide fluoroimmunoassay), a time resolved fluorescence method, to quantitate whole venom specific and allergenic peptide-specific IgE (sIgE), sIgG(1) and sIgG(4) in serum from people clinically allergic to Australian native ant venoms, of which the predominant cause of allergy is jack jumper ant venom (JJAV). Intra-assay CV was 6.3% and inter-assay CV was 13.7% for JJAV sIgE. DELFIA and Phadia CAP JJAV sIgE results correlated well and had similar sensitivity and specificity for the detection of JJAV sIgE against intradermal skin testing as the gold standard. DELFIA was easily adapted for detecting sIgE to a panel of other native ant venoms.

Elevated serum cytokines during human anaphylaxis: Identification of potential mediators of acute allergic reactions.

BACKGROUND: Anaphylaxis is generally unanticipated and requires emergency management. Therefore, the biological mediators in human beings have been difficult to define. OBJECTIVE: Our aim was to identify cytokines and chemokines whose concentrations increase during anaphylaxis in human beings and to determine how each correlates with severity. METHODS: We measured the concentrations of potential mediators, including cytokines, chemokines, mast cell tryptase (MCT), and histamine, over 3 time points in 76 patients presenting to emergency departments with anaphylaxis and correlated these with a global severity scale, hypotension, and hypoxia. RESULTS: IL-2, IL-6, IL-10, TNF receptor I, MCT, and histamine were significantly elevated in patients with severe reactions (n = 36) compared with moderate reactions (n = 40) and healthy controls. Histamine levels peaked at emergency department arrival, whereas other mediators peaked later. IL-4, IL-5, IL-13, IFN-gamma, and TNF-alpha were marginally elevated in severe reactions compared with healthy controls but did not correlate with reaction severity. Severe reactions tended to be either hypotensive (n = 19) or hypoxemic (n = 12). Levels of IL-6, IL-10, TNF receptor I, MCT, and histamine correlated with hypotension. No mediator correlated with hypoxemia or other respiratory features. CONCLUSION: This study confirms that the concentrations of a number of cytokines are elevated in blood during anaphylaxis in human beings and that some correlate with the presence of hypotension. Others were only marginally elevated within a concentration range that available assays do not reliably detect. During respiratory reactions, mediators may be largely confined to the airways so that blood concentrations do not reflect activity.

The number and function of circulating dendritic cells may limit effector memory CD4+ T-cell responses in HIV patients responding to antiretroviral therapy.

Some HIV patients who previously experienced severe immunodeficiency retain low pathogen-specific T-cell responses despite a virological response to antiretroviral therapy (ART). To identify correlates with dysfunction in accessory cell populations, HIV patients were stratified into groups maintaining high or low CD4(+) T-cell IFN-gamma responses to cytomegalovirus (CMV) over 4-8 years on ART. Myeloid dendritic cells (mDC), plasmacytoid (p) DC, M-DC8(+) cells and monocytes were enumerated and mRNA of cytokines and activation molecules were quantitated in purified subpopulations. Proportions of pDC were lower (p=0.043) and mDC were higher (p=0.043) in low responders. TRAIL receptor 2 (DR5) mRNA levels in pDC (p=0.0008) and mDC (p=0.0062) were lower in high responders compared to controls. Levels of IL-15 mRNA were higher in mDC from high responders (p=0.015) and levels of IL-10 mRNA were higher in M-DC8(+) cells from low responders (p=0.036). Hence CMV-specific CD4(+) T-cell IFN-gamma responses may be affected by numbers and function of circulating DC.

Monitoring clinical trials of therapeutic vaccines in HIV infection: role of treatment interruption.

PURPOSE OF REVIEW: To outline the rationale for testing therapeutic vaccines in HIV infection and to discuss the ways in which the antiviral activities of these vaccination trials can be evaluated. In the era of highly active antiretroviral therapy, analytical treatment interruption has served as the gold standard to evaluate therapeutic vaccine strategies. RECENT FINDINGS: In the era before the introduction of highly active antiretroviral therapy, therapeutic vaccine trials showed minimal evidence of antiviral activity. It is not clear whether these failures reflect the immune suppressive effects of HIV replication or the inadequacy of early vaccine constructs and strategies. Recent studies have provided some optimism that therapeutic vaccine strategies may be effective in chronic established infection and perhaps even in chronic HIV infection. Approaches to evaluate the activities of candidate therapeutic vaccine strategies in the era of antiretroviral therapy have included analytical treatment interruptions, but recently the safety of this has been called into question. SUMMARY: Although analytical treatment interruption remains the current standard for evaluating the antiviral activities of therapeutic immunization strategies in established HIV infection, other methods and strategies may prove useful and should be evaluated.

Interferon-gamma responses to Candida recover slowly or remain low in immunodeficient HIV patients responding to ART.

Extended assessments of memory T-cell responses in HIV patients who have a satisfactory virological response to combination antiretroviral therapy (CART) have been limited by availability of longitudinal samples and of antigens to which most individuals (including HIV-negative controls) have been exposed. Studies of cytomegalovirus (CMV) show that interferon-gamma (IFN-gamma) responses never recover completely, but this may be antigen-specific. Here we present responses to Candida and CMV antigens analyzed using a statistical approach that derives overall trends from samples collected at variable time points. Results were considered in relation to putative markers of T-regulatory cells. Blood mononuclear cells collected from seventeen HIV-1 patients (nadir <100 CD4 T cells/mL) 0-8 years after initiation of CART were stimulated with Candida spp lysate, Candida enolase protein or CMV lysate and production of IFN-gamma was assessed by ELISpot assay. CD4 T-cell counts increased fivefold and stabilized within 24 months on CART, following control of plasma viremia. IFN-gamma responses to Candida antigens began low and increased slowly, generating positive slope up to 60 months on CART (Candida enolase p=0.008; Candida lysate p=0.03; mixed-model Wald test). Only two patients displayed a CMV or Candida-specific IFN-gamma response above the median for seronegative controls. Proportions of T cells expressing CD25 or CD57 did not correlate with IFN-gamma responses. Slow reconstitution of IFN-gamma responses to CMV and Candida in previously immunodeficient patients with restored CD4+ T-cell counts on CART suggests a broad and nonresolving defect in memory T-cell responses.

HIV patients on antiretroviral therapy have high frequencies of CD8 T cells specific for Immediate Early protein-1 of cytomegalovirus.

OBJECTIVE: To assess the frequency and phenotype of cytomegalovirus (CMV)-specific CD8 T cells in previously immunocompromised HIV patients with stable undetectable HIV viremia due to highly active antiretroviral therapy (HAART). METHODS: Twenty-one CMV-seropositive HIV patients with nadir CD4 T-cell counts < 50 x 10(6) cells/l, at least 4 years on HAART and 6 months of complete viral suppression (< 50 HIV RNA copies/ml) and 12 CMV-seropositive, HIV-seronegative age/sex-matched controls were studied. CD4 and CD8 T-cell responses to whole CMV and two HLA-A*02 restricted CMV peptides [NLV from pp65 and VLE from Immediate Early 1 (IE1)] were measured by interferon (IFN)gamma ELISpot. Phenotypes of peptide-specific CD8 T cells were determined by tetramer staining. RESULTS: In the ELISpot assay, HIV patients had significantly more CD8 T cells producing IFN gamma in response to VLE than controls, whereas numbers of NLV-specific and CMV-specific IFN gamma spots were similar. Four HIV patients and one control had large VLE and/or NLV-specific CD8 T-cell populations despite the absence of CMV-specific CD4 T cells. The majority of peptide-specific CD8 T cells from HIV patients and controls were CD28-, CD45RO+ and CD45RA-. However, a significantly higher proportion of VLE-specific CD8 T cells expressed perforin compared to NLV-specific CD8 T cells in HIV patients. CONCLUSIONS: HIV patients had elevated numbers of IE1-specific, IFNgamma-producing perforin-positive CD8 T cells compared to controls. As IE1 is expressed early during CMV reactivation, these cells may be important for preventing CMV replication to pathogenic levels. In addition, CMV-specific CD4 T cells are not essential for maintenance of large populations of CMV-specific CD8 T cells in aviremic HIV patients on HAART.

Immune restoration disease: a consequence of dysregulated immune responses after HAART.

Immune Restoration Diseases (IRD) are a collection of atypical 'opportunistic infections' and inflammatory diseases seen in human immunodeficiency virus (HIV) patients after HIV viraemia is suppressed by highly active antiretroviral therapy (HAART). IRD probably reflect dysregulated immune responses against pre-existing infections by opportunistic pathogens, with different immunopathological mechanisms for different pathogens. For example, mycobacterial IRD are associated with delayed type hypersensitivity (DTH) responses to mycobacterial antigens, whereas patients who experience cytomegalovirus (CMV) IRD have elevated plasma levels of soluble CD30, a marker of a T2 cytokine environment expressed by activated CD8 T-cells. As IRD are often compartmentalised to organs, monitoring serological markers such as pathogen-specific IgG antibody, may be informative, as demonstrated for CMV and hepatitis C virus (HCV)-associated IRD. Genetic studies have provided evidence of distinct immunopathological mechanisms and inherited susceptibility to IRD associated with mycobacterial and herpesviridae infections. The expansion of HAART in the developing world where many HIV patients have low CD4+ T-cell counts and high rates of concomitant infections will place a large number of patients at-risk of developing IRD. It is therefore important to understand the immunopathology so that prevention, diagnosis and treatment can be improved.

Immune restoration disease after antiretroviral therapy.

Suppression of HIV replication by highly active antiretroviral therapy (HAART) often restores protective pathogen-specific immune responses, but in some patients the restored immune response is immunopathological and causes disease [immune restoration disease (IRD)]. Infections by mycobacteria, cryptococci, herpesviruses, hepatitis B and C virus, and JC virus are the most common pathogens associated with infectious IRD. Sarcoid IRD and autoimmune IRD occur less commonly. Infectious IRD presenting during the first 3 months of therapy appears to reflect an immune response against an active (often quiescent) infection by opportunistic pathogens whereas late IRD may result from an immune response against the antigens of non-viable pathogens. Data on the immunopathogenesis of IRD is limited but it suggests that immunopathogenic mechanisms are determined by the pathogen. For example, mycobacterial IRD is associated with delayed-type hypersensitivity responses to mycobacterial antigens whereas there is evidence of a CD8 T-cell response in herpesvirus IRD. Furthermore, the association of different cytokine gene polymorphisms with mycobacterial or herpesvirus IRD provides evidence of different pathogenic mechanisms as well as indicating a genetic susceptibility to IRD. Differentiation of IRD from an opportunistic infection is important because IRD indicates a successful, albeit undesirable, effect of HAART. It is also important to differentiate IRD from drug toxicity to avoid unnecessary cessation of HAART. The management of IRD often requires the use of anti-microbial and/or anti-inflammatory therapy. Investigation of strategies to prevent IRD is a priority, particularly in developing countries, and requires the development of risk assessment methods and diagnostic criteria.