Intrinsic risk factors for alpha-gal syndrome in a case-control study, 2019 to 2020.

BACKGROUND: Alpha-gal syndrome (AGS) is an allergy to galactose-α-1,3-galactose (alpha-gal), a carbohydrate found in most mammals. Evidence indicates that AGS develops after a tick bite, and in the United States, AGS is most associated with bites from Amblyomma americanum (lone star tick); however, not all persons bitten by ticks develop clinical AGS. OBJECTIVE: To investigate intrinsic risk factors associated with the development of AGS. METHODS: We performed a case-control study among adults presenting for diagnosis or management of AGS at an allergy clinic in North Carolina during 2019 to 2020 and compared them with controls enrolled from 2 nearby internal medicine clinics. A questionnaire gathered epidemiologic and tick exposure data, and blood was obtained for alpha-gal-specific IgE and other testing. RESULTS: The 82 enrolled case patients and 191 controls did not differ significantly by age or sex. Case patients were more likely than controls to have A or O blood types (non B-antigen), have experienced childhood allergies, and have a family history of AGS and other food allergies. Case patients were also more likely to report experiencing long healing times for insect bites or stings and a family history of allergy to stinging or biting insects. CONCLUSION: This study suggested that intrinsic factors contribute to risk of developing AGS. Some traits are genetic, but common behaviors among households and family units likely also contribute. Identification of these risk factors can inform personal risk, aid health care providers in understanding susceptible populations, and contribute to ongoing understanding of AGS epidemiology.

Development of anti-PEG IgG/IgM/IgE ELISA assays for profiling anti-PEG immunoglobulin response in PEG-sensitized individuals and patients with alpha-gal allergy.

Polyethylene glycol (PEG) is frequently used in various protein and nanomedicine therapeutics. However, various studies have shown that select PEGylated therapeutics can induce production of anti-PEG antibodies (APA), potentially culminating in rapid clearance from the systemic circulation, loss of efficacy and possibly increased risks of allergic reactions. Although IgE is a frequent cause of immediate hypersensitivity reactions (IHR), the role of IgE APA in PEG-related IHR is not well understood, due in part to a lack of standardized assays for measuring IgE APA. Here, we developed a rigorous competitive ELISA method to measure the concentrations of various APA isotypes, including IgE, with picomolar sensitivities. In a small number of serum samples from patients with known PEG allergy, the assay allowed us to detect a strong correlation between IgG and IgE APA in individuals with history of allergic reactions to PEG or PEGylated drugs, but not between IgM and IgE APA. We detected appreciable levels of IgG and IgM APA in individuals with history of alpha-gal allergy, however, they were not elevated relative to those detected in other healthy controls, and we found no pre-existing IgE APA. While preliminary and should be further investigated, these results suggest that differences in the route and mechanism of PEG exposure may drive variability in APA response.

Tick-Borne Disease Infections and Chronic Musculoskeletal Pain.

Importance: Tick-borne diseases (TBDs) other than Lyme disease, such as spotted fever group rickettsiosis, ehrlichiosis, and galactose-α-1,3-galactose (α-gal) syndrome, are an emerging public health issue. Long-term sequelae secondary to Ehrlichia or Rickettsia infection are uncommon; however, musculoskeletal symptoms are often attributed to prior tick exposure. Objective: To evaluate the potential associations between prior exposure to TBDs and musculoskeletal symptoms, including radiographic osteoarthritis. Design, Setting, and Participants: This cross-sectional study analyzed serum samples from the fourth visit (2017-2018) of the Johnston County Osteoarthritis (JoCo OA) project, an ongoing longitudinal, population-based study in Johnston County, North Carolina. Biospecimen testing and analysis were performed between May 2022 and November 2023. Participants in the JoCo OA project are noninstitutionalized White and Black Johnston County residents 45 years or older. Main Outcome and Measures: The primary outcome was seropositivity with Ehrlichia IgG, Rickettsia IgG, and/or α-gal IgE and musculoskeletal symptoms. Secondary outcomes included risk factors associated with elevated α-gal IgE and weighted population point prevalence rates. Participants completed questionnaires, underwent physical assessments, and provided biospecimens for serological testing. Multivariable models were used to estimate associations of interest. Results: Of the 605 participants who completed the fourth visit of the JoCo OA project, 488 (80.7%) had serum samples available for testing. The 488 participants had a median (IQR) age of 72 (68-78) years and included 336 females (68.9%) and 161 Black (33.0%) and 327 White (67.0%) individuals. The overall weighted point prevalence was 8.6% (95% CI, 5.9%-11.3%) for Ehrlichia IgG, 17.1% (95% CI, 12.6%-21.5%) for Rickettsia IgG, and 19.6% (95% CI, 15.3%-23.8%) for α-gal IgE level greater than 0.1 IU/mL. Only α-gal IgE was associated with knee pain, aching or stiffness (mean ratio, 1.30; 95% CI, 1.09-1.56). Antibodies to Rickettsia, Ehrlichia, and α-gal were not associated with symptomatic radiographic knee osteoarthritis. Male sex (odds ratio [OR], 2.63; 95% CI, 1.55-4.47), current smoker status (OR, 3.55; 95% CI, 1.38-9.18), and an attached tick bite in the past 5 years (OR, 3.99; 95% CI, 2.22-7.15) were all risk factors that were associated with α-gal IgE level greater than 0.1 IU/mL. Despite only 84 individuals (17.2%) recalling a tick bite in the past 5 years, 178 (36.5%) had evidence of prior tick-borne exposure, suggesting frequent human-tick interactions. Conclusions and Relevance: Results of this cross-sectional study indicate no association between Ehrlichia or Rickettsia seropositivity and chronic musculoskeletal symptoms or osteoarthritis. Further investigation is needed into the pathogenesis of α-gal syndrome and interventions to reduce human-tick interactions.

Tick bite-induced Alpha-Gal Syndrome and Immunologic Responses in an Alpha-Gal Deficient Murine Model.

Introduction: Alpha-Gal Syndrome (AGS) is a delayed allergic reaction due to specific IgE antibodies targeting galactose-α-1,3-galactose (α-gal), a carbohydrate found in red meat. This condition has gained significant attention globally due to its increasing prevalence, with more than 450,000 cases estimated in the United States alone. Previous research has established a connection between AGS and tick bites, which sensitize individuals to α-gal antigens and elevate the levels of α-gal specific IgE. However, the precise mechanism by which tick bites influence the hosts immune system and contribute to the development of AGS remains poorly understood. This study investigates various factors related to ticks and the host associated with the development of AGS following a tick bite, using mice with a targeted disruption of alpha-1,3-galactosyltransferase (AGKO) as a model organism. Methods: Lone-star tick (Amblyomma americanum) and gulf-coast tick (Amblyomma maculatum) nymphs were used to sensitize AGKO mice, followed by pork meat challenge. Tick bite site biopsies from sensitized and non-sensitized mice were subjected to mRNA gene expression analysis to assess the host immune response. Antibody responses in sensitized mice were also determined. Results: Our results showed a significant increase in the titer of total IgE, IgG1, and α-gal IgG1 antibodies in the lone-star tick-sensitized AGKO mice compared to the gulf-coast tick-sensitized mice. Pork challenge in Am. americanum -sensitized mice led to a decline in body temperature after the meat challenge. Gene expression analysis revealed that Am. americanum bites direct mouse immunity toward Th2 and facilitate host sensitization to the α-gal antigen, while Am. maculatum did not. Conclusion: This study supports the hypothesis that specific tick species may increase the risk of developing α-gal-specific IgE and hypersensitivity reactions or AGS, thereby providing opportunities for future research on the mechanistic role of tick and host-related factors in AGS development.

Tick bite as a risk factor for alpha-gal-specific immunoglobulin E antibodies and development of alpha-gal syndrome.

BACKGROUND: The disaccharide galactose-α-1,3-galactose (alpha-gal) is expressed in mammals other than humans, apes, and old-world monkeys. In humans, elevated immunoglobulin E (IgE) antibodies specific for alpha-gal can result in allergic hypersensitivity known as alpha-gal syndrome (AGS). Case reports and series suggest that tick bites can induce alpha-gal-specific IgE (sIgE) antibodies. OBJECTIVE: To evaluate tick exposure as a risk factor for AGS and elevated alpha-gal sIgE level. METHODS: We conducted a case-control study comparing patients with AGS from a North Carolina allergy clinic with controls who were patients at a nearby internal medicine clinic. Cases and controls were administered a questionnaire to obtain information about demographics, home environment, outdoor activities, and recollection of tick bite. Serum samples taken at the time of enrollment were tested for total IgE, alpha-gal sIgE, and antibodies to other tick-borne pathogens. RESULTS: The patients with AGS were more likely to recall finding a tick on themselves (odds ratio [OR], 11.20; 95% confidence interval [CI], 4.97-25.15), live near wooded forest (OR, 2.27; 95% CI, 0.92-5.55), and spend 17 or more hours per week outdoors in wooded areas (OR, 5.58; 95% CI, 2.56-12.19). The patients with AGS were also more likely to report 4 or more tick bites (OR, 33.05; 95% CI, 9.92-155.12) and reactions at the site of tick bites (OR, 7.93; 95% CI, 3.74-16.80). Furthermore, elevated alpha-gal sIgE level was observed in 33% of the controls and was associated with tick exposure in the controls (OR, 4.25; 95% CI, 2.21-8.18). CONCLUSION: The results define tick bite as a risk factor for AGS and elevated alpha-gal sIgE level.

Tick bite-induced alpha-gal syndrome and immunologic responses in an alpha-gal deficient murine model.

Introduction: Alpha-Gal Syndrome (AGS) is a delayed allergic reaction due to specific IgE antibodies targeting galactose-α-1,3-galactose (α-gal), a carbohydrate found in red meat. This condition has gained significant attention globally due to its increasing prevalence, with more than 450,000 cases estimated just in the United States alone. Previous research has established a connection between AGS and tick bites, which sensitize individuals to α-gal antigens and elevate the levels of specific IgE. However, the precise mechanism by which tick bites influence the host's immune system and contribute to the development of AGS remains poorly understood. This study investigates various factors related to ticks and the host associated with the development of AGS following a tick bite, using mice with a targeted disruption of alpha-1,3-galactosyltransferase (AGKO) as a model organism. Methods: Lone-star tick (Amblyomma americanum) and gulf-coast tick (Amblyomma maculatum) nymphs were used to sensitize AGKO mice, followed by pork meat challenge. Tick bite site biopsies from sensitized and non-sensitized mice were subjected to mRNA gene expression analysis to assess the host immune response. Antibody responses in sensitized mice were also determined. Results: Our results showed a significant increase in the total IgE, IgG1, and α-gal IgG1 antibodies titers in the lone-star tick-sensitized AGKO mice compared to the gulf-coast tick-sensitized mice. Pork challenge in Am. americanum -sensitized mice led to a decline in body temperature after the meat challenge. Gene expression analysis revealed that Am. americanum bites direct mouse immunity toward Th2 and facilitate host sensitization to the α-gal antigen. Conclusion: This study supports the hypothesis that specific tick species may increase the risk of developing α-gal-specific IgE and hypersensitivity reactions or AGS, thereby providing opportunities for future research on the mechanistic role of tick and host-related factors in AGS development.

Allergic response to medical products in patients with alpha-gal syndrome.

BACKGROUND: Galactose-α-1,3-galactose (alpha-gal) is a carbohydrate that is ubiquitously expressed in all mammals except for primates and humans. Patients can become sensitized to this antigen and develop alpha-gal syndrome (AGS), or a red meat allergy. Symptoms range from generalized gastroenteritis and malaise to anaphylaxis, and in endemic areas, the prevalence can be as high as 20%. Although AGS patients commonly avoid alpha-gal by avoiding meat, patients have also developed symptoms due to animal-derived medical products and devices. With the rise in transcatheter aortic valve replacement, we investigate the immunogenicity of common cardiac materials and valves. OBJECTIVE: To assess the in vitro immunoglobulin E response toward common medical products, including cardiac patch materials and bioprosthetic valves in patients with AGS. METHODS: Immunoblot and immunohistochemistry techniques were applied to assess immunoglobulin E reactivity to various mammalian derived tissues and medical products for patients with AGS. RESULTS: AGS serum showed strong reactivity to all of the commercially available, nonhuman products tested, including various decellularized cardiac patch materials and bioprosthetic aortic valves. AGS serum did not react to tissues prepared using alpha-gal knockout pigs. CONCLUSIONS: Despite commercial decellularization processes, alpha-gal continues to be present in animal-derived medical products, including bioprosthetic valves. Serum from patients with AGS demonstrates a strong affinity for these products in vitro. This may have serious potential implications for sensitized patients undergoing cardiac surgery, including early valve failure and accelerated coronary artery disease.

Tick salivary gland extract induces alpha-gal syndrome in alpha-gal deficient mice.

INTRODUCTION: Alpha-gal syndrome (AGS) is characterized by delayed hypersensitivity to non-primate mammalian meat in people having specific immunoglobulin E (sIgE) to the oligosaccharide galactose-alpha-1,3-galactose. AGS has been linked to tick bites from Amblyomma americanum (Aa) in the U.S. A small animal model of meat allergy is needed to study the mechanism of alpha-gal sensitization, the effector phase leading to delayed allergic responses and potential therapeutics to treat AGS. METHODS: Eight- to ten-weeks old mice with a targeted inactivation of alpha-1,3-galactosyltransferase (AGKO) were injected intradermally with 50 µg of Aa tick salivary gland extract (TSGE) on days 0, 7, 21, 28, 42, and 49. Total IgE and alpha-gal sIgE were quantitated on Day 56 by enzyme-linked immunosorbent assay. Mice were challenged orally with 400 mg of cooked pork kidney homogenate or pork fat. Reaction severity was assessed by measuring a drop in core body temperature and scoring allergic signs. RESULTS: Compared to control animals, mice treated with TSGE had 190-fold higher total IgE on Day 56 (0.60 ± 0.12 ng/ml vs. 113.2 ± 24.77 ng/ml; p < 0.001). Alpha-gal sIgE was also produced in AGKO mice following TSGE sensitization (undetected vs. 158.4 ± 72.43 pg/ml). Further, sensitized mice displayed moderate clinical allergic signs along with a drop in core body temperature of ≥2°C as an objective measure of a systemic allergic reaction. Interestingly, female mice had higher total IgE responses to TSGE treatment but male mice had larger declines in mean body temperature. CONCLUSION: TSGE-sensitized AGKO mice generate sIgE to alpha-gal and demonstrate characteristic allergic responses to pork fat and pork kidney. In keeping with the AGS responses documented in humans, mice reacted more rapidly to organ meat than to high fat pork challenge. This mouse model establishes the central role of tick bites in the development of AGS and provides a small animal model to mechanistically study mammalian meat allergy.

T and B Lymphocyte Transcriptional States Differentiate between Sensitized and Unsensitized Individuals in Alpha-Gal Syndrome.

The mechanisms of pathogenesis driving alpha-gal syndrome (AGS) are not fully understood. Differences in immune gene expression between AGS individuals and non-allergic controls may illuminate molecular pathways and targets critical for AGS development. We performed immune expression profiling with RNA from the peripheral blood mononuclear cells (PBMCs) of seven controls, 15 AGS participants, and two participants sensitized but not allergic to alpha-gal using the NanoString nCounter PanCancer immune profiling panel, which includes 770 genes from 14 different cell types. The top differentially expressed genes (DEG) between AGS subjects and controls included transcription factors regulating immune gene expression, such as the NFκB pathway (NFKBIA, NFKB2, REL), antigen presentation molecules, type 2/allergic immune responses, itch, and allergic dermatitis. The differential expression of genes linked to T and B cell function was also identified, including transcription factor BCL-6, markers of antigen experience (CD44) and memory (CD27), chemokine receptors (CXCR3, CXCR6), and regulators of B-cell proliferation, cell cycle entry and immunoglobulin production (CD70). The PBMCs from AGS subjects also had increased TNF and IFN-gamma mRNA expression compared to controls. AGS is associated with a distinct gene expression profile in circulating PBMCs. DEGs related to antigen presentation, antigen-experienced T-cells, and type 2 immune responses may promote the development of alpha-gal specific IgE and the maintenance of AGS.

Food Allergy.

PURPOSE OF REVIEW: The goal of this review is to present an updated summary of the natural history of major childhood and adult food allergies and report recent advances in potential treatments for food allergy. RECENT FINDINGS: The most common childhood food allergies are typically outgrown by adolescence or adulthood. However, peanut/tree nut allergies appear to more commonly persist into adulthood. Adults can develop new IgE-mediated food allergies; the most common is oral allergy syndrome. There are multiple different approaches being tried as possible treatments for food allergy. The prevalence of food allergy appears to be increasing but the varied approaches to treatment are being actively pursued such that an approved modality may not be too far in the future.

Targeted cytotoxic therapy kills persisting HIV infected cells during ART.

Antiretroviral therapy (ART) can reduce HIV levels in plasma to undetectable levels, but rather little is known about the effects of ART outside of the peripheral blood regarding persistent virus production in tissue reservoirs. Understanding the dynamics of ART-induced reductions in viral RNA (vRNA) levels throughout the body is important for the development of strategies to eradicate infectious HIV from patients. Essential to a successful eradication therapy is a component capable of killing persisting HIV infected cells during ART. Therefore, we determined the in vivo efficacy of a targeted cytotoxic therapy to kill infected cells that persist despite long-term ART. For this purpose, we first characterized the impact of ART on HIV RNA levels in multiple organs of bone marrow-liver-thymus (BLT) humanized mice and found that antiretroviral drug penetration and activity was sufficient to reduce, but not eliminate, HIV production in each tissue tested. For targeted cytotoxic killing of these persistent vRNA(+) cells, we treated BLT mice undergoing ART with an HIV-specific immunotoxin. We found that compared to ART alone, this agent profoundly depleted productively infected cells systemically. These results offer proof-of-concept that targeted cytotoxic therapies can be effective components of HIV eradication strategies.

Latent HIV-1 infection of resting CD4⁺ T cells in the humanized Rag2⁻/⁻ γc⁻/⁻ mouse.

Persistent human immunodeficiency virus type 1 (HIV-1) infection of resting CD4⁺ T cells, unaffected by antiretroviral therapy (ART), provides a long-lived reservoir of HIV infection. Therapies that target this viral reservoir are needed to eradicate HIV-1 infection. A small-animal model that recapitulates HIV-1 latency in resting CD4⁺ T cells may accelerate drug discovery and allow the rational design of nonhuman primate (NHP) or human studies. We report that in humanized Rag2⁻/⁻ γ(c)⁻/⁻ (hu-Rag2⁻/⁻ γ(c)⁻/⁻) mice, as in humans, resting CD4⁺ T cell infection (RCI) can be quantitated in pooled samples of circulating cells and tissue reservoirs (e.g., lymph node, spleen, bone marrow) following HIV-1 infection with the CCR5-tropic JR-CSF strain and suppression of viremia by ART. Replication-competent virus was recovered from pooled resting CD4⁺ T cells in 7 of 16 mice, with a median frequency of 8 (range, 2 to 12) infected cells per million T cells, demonstrating that HIV-1 infection can persist despite ART in the resting CD4⁺ T cell reservoir of hu-Rag2⁻/⁻ γ(c)⁻/⁻ mice. This model will allow rapid preliminary assessments of novel eradication approaches and combinatorial strategies that may be challenging to perform in the NHP model or in humans, as well as a rigorous analysis of the effect of these interventions in specific anatomical compartments.

Generation of HIV latency in humanized BLT mice.

Here we demonstrate that a combination of tenofovir, emtricitabine, and raltegravir effectively suppresses peripheral and systemic HIV replication in humanized BLT mice. We also demonstrate that antiretroviral therapy (ART)-treated humanized BLT mice harbor latently infected resting human CD4+ T cells that can be induced ex vivo to produce HIV. We observed that the levels of infected resting human CD4+ T cells present in BLT mice are within the range of those observed circulating in patients undergoing suppressive ART. These results demonstrate the potential of humanized BLT mice as an attractive model for testing the in vivo efficacy of novel HIV eradication strategies.

Curing HIV: Pharmacologic approaches to target HIV-1 latency.

HIV-1 infection persists even after years of antiretroviral therapy (ART). Although ART can halt viral replication and thereby reduce viremia to clinically undetectable levels, proviral latency established within the host genome remains largely unaffected by ART and can replenish systemic infection following interruption of therapy. Pharmacologic strategies, which not only target viral replication but also deplete proviral infection, are required for successful clearance of HIV-1 infection. This review highlights the current understanding of molecular mechanisms that establish and maintain HIV-1 latency in its major reservoir, the resting memory CD4(+) T cell. We also identify the molecular targets that might be exploited to induce HIV-1 expression, remove epigenetic restrictions, or enhance effective transcription. Finally, we discuss the potential pharmacologic approaches toward targeting viral persistence in different cellular and anatomical reservoirs to achieve a cure of HIV-1 infection.

Suppression of human immunodeficiency virus type 1 (HIV-1) viremia with reverse transcriptase and integrase inhibitors, CD4+ T-cell recovery, and viral rebound upon interruption of therapy in a new model for HIV treatment in the humanized Rag2-/-{gamma}c-/- mouse.

A small animal model that reproduces human immunodeficiency virus type 1 (HIV-1) pathogenesis may allow modeling of new therapeutic strategies in ways not approachable in mononuclear cell culture. We find that, as in humans, combination antiretroviral therapy (ART) in humanized (hu-) Rag2(-/-)gamma(c)(-/-) mice allows suppression of viremia below the limits of detection and recovery of CD4(+) cells, while interruption of ART results in viral rebound and renewed loss of CD4(+) T cells. Failure of ART in infected mice is associated with the appearance of drug resistance mutations. The hu-Rag2(-/-)gamma(c)(-/-) mouse may therefore facilitate testing of novel approaches to HIV replication and persistence.

Hexamethylbisacetamide and disruption of human immunodeficiency virus type 1 latency in CD4(+) T cells.

BACKGROUND: Novel therapeutic approaches are needed to attack persistent proviral human immunodeficiency type 1 (HIV-1) infection. Hexamethylbisacetamide (HMBA), a hybrid bipolar compound, induces expression of the HIV-1 promoter in the long terminal repeat (LTR) region in a Tat-independent manner but mimics the effect of Tat, overcoming barriers to LTR expression and increasing the processivity of LTR transcription complexes. METHODS: We studied alterations in cellular factors and their LTR occupancy induced by HMBA in models of latent HIV-1 infection. We measured the induction of viral outgrowth by HMBA in resting CD4(+) T cells from aviremic HIV-1-infected donors. RESULTS: HMBA induced outgrowth of HIV-1 from resting CD4(+) T cells recovered from aviremic patients treated with antiretroviral therapy (ART). HMBA triggered cyclin-dependent kinase 9 (CDK9) recruitment to the LTR, a key factor in the induction of efficient HIV-1 expression, via an unexpected interaction with the transcription factor Sp1. The availability of Sp1 and Sp1 DNA binding sites were necessary for HMBA-induced CDK9 recruitment and LTR expression. HMBA signaling via both protein kinase C mu and phosphatidylinositol 3-kinase appeared to contribute to LTR induction. CONCLUSIONS: The novel mechanism through which HMBA disrupts latent HIV-1 infection involves 2 cellular kinases that may be therapeutically exploited to induce expression of persistent proviral HIV-1.

Low immune activation despite high levels of pathogenic human immunodeficiency virus type 1 results in long-term asymptomatic disease.

Long-term asymptomatic human immunodeficiency virus (HIV)-infected individuals (LTA) usually have low viral load and low immune activation. To discern whether viral load or immune activation is dominant in determining progression to AIDS, we studied three exceptional LTA with high viral loads. HIV type 1 isolates from these LTA were as pathogenic as viruses from progressors in organ culture. Despite high viral loads, these LTA had low levels of proliferating and activated T cells compared to progressors, like other LTA. In contrast to those in progressors, HIV-specific CD4(+) T-cell responses in these LTA were maintained. Thus, low immune activation despite a high viral load preserved HIV-specific T-cell responses and resulted in a long-term asymptomatic phenotype.

CXCR4 tropic human immunodeficiency virus type 1 induces an apoptotic cascade in immature infected thymocytes that resembles thymocyte negative selection.

HIV-1 often replicates in the thymus of infected individuals, causing thymocyte depletion and thymic dysfunction. Nevertheless, the mechanisms by which thymocyte depletion occurs are not clear. Here we report that HIV-1 infection induced apoptosis primarily in productively infected thymocytes; aldrithiol-2 or Efavirenz treatment largely abrogated HIV-1-induced apoptosis. Moreover, X4-HIV-1 induced apoptosis primarily in immature CD4+ CD8+ (DP) thymocytes whereas most mature CD4 or CD8 single-positive (SP) thymocytes were resistant to X4 HIV-1-induced apoptosis despite infection. Consistent with this, we observed significant induction of several genes involved in negative selection of DP thymocytes. Furthermore, treatment of thymocytes with cycloheximide abrogated HIV-1-induced apoptosis, implying a requirement for de novo protein synthesis. Our results suggest that HIV-1-induced apoptosis of thymocytes requires the activation of caspases and the participation of mitochondrial apoptosis effectors, which serve to amplify the apoptotic signal, a process similar to that elaborated during thymocyte negative selection.

R5 human immunodeficiency virus type 1 infection of fetal thymic organ culture induces cytokine and CCR5 expression.

Late-stage CCR5 tropic human immunodeficiency virus type 1 (HIV-1) isolates (R5 HIV-1) can deplete nearly all CD4+ thymocytes from human thymus/liver grafts, despite the fact that fewer than 5% of these cells express CCR5. To resolve this paradox, we studied the replication and cytopathic effects (CPE) of late-stage R5 HIV-1 biological clones from two progressors and two long-term nonprogressors (LTNP) in fetal thymic organ culture (FTOC) with and without added cytokines. We found that R5 HIV-1 clones from progressors but not LTNP were cytopathic in untreated FTOC. Moreover, R5 HIV-1 clones from progressors replicated to higher levels than LTNP-derived R5 HIV-1 clones in this system. In contrast, when FTOC was maintained in the presence of interleukin 2 (IL-2), IL-4, and IL-7, both progressor and LTNP clones exhibited similar replication and CPE, which were equal to or greater than the levels achieved by progressor-derived R5 HIV-1 clones in untreated FTOC. This finding was likely due to IL-2-induced CCR5 expression on CD4+ thymocytes in FTOC. R5 HIV-1 clones showed greater pathogenesis for CCR5+ cells but also showed evidence of CPE on CCR5- cells. Furthermore, infection of FTOC by R5 HIV-1 induced IL-10 and transforming growth factor beta (TGF-beta) expression. Both IL-10 and TGF-beta in turn induced CCR5 expression in FTOC. Induction of CCR5 expression via cytokine induction by R5 HIV-1 infection of CCR5+ thymocytes likely permitted further viral replication in newly CCR5+ thymocytes. CCR5 expression, therefore, is a key determinant of pathogenesis of R5 HIV-1 in FTOC.