Deficiency of the CD3-TCR signal pathway in three patients with idiopathic CD4+ lymphocytopenia

Idiopathic CD4+ lymphocytopenia (ICL) is a rare syndrome affecting adults and defined by a stable loss of CD4+ T cells in the absence of any known cause of immune deficiency. Defective T-cell proliferations to mitogens and antigens have been described in some of such patients displaying clinical signs of immune deficiency such as opportunistic infections. We investigated here the hypothesis that T-cell depletion and dysfunction could be due to biochemical defects of the CD3-TCR pathway in CD4+ and/or CD8+ subsets from three patients with severe stable ICL (below 150 CD4+ T cells/microliter) and opportunistic infections. Patient 1 had a general T lymphocytopenia, whereas patients 2 and 3 displayed a selective loss of CD4+ T cells. We observed in all patients a major reduction of the proliferative response to CD3-TCR stimulation that affected only the depleted T-cell subpopulation. Moreover, in two cases, impaired early biochemical events of the CD3-TCR pathway were detected. In patient 1 and 3, we found a defect (of distinct intensity) of CD3-induced protein tyrosine phosphorylation in CD4+ cells compared to control cells, whereas this process was normally induced in CD4+ T cells from patient 2. Taken together, this study reveals that the heterogeneity of the ICL syndrome was situated at the cellular level, and involved in two cases abnormalities of transducing molecules of the CD3-TCR pathway.     

A new syndrome of long-term idiopathic, severe CD4+ lymphocytopenia: isolated paraparesis and conjunctival ischemic microangiopathy

An extraordinary case report of an adult patient followed-up for a decade with an extremely severe idiopathic CD4+ T-lymphocytopenia (as expressed by an absolute CD4+ count of 8-25 cells/microL), associated with an isolated paraparesis and a conjunctival ischemic microangiopathy is described, and discussed on the grounds of the available literature. Despite such a severe and prolonged immunodeficiency, no opportunistic disease occurred, in a observation period longer than ever reported to date. The neurological disorder was diagnosed concurrently with idiopathic CD4+ lymphocyte depletion, while the ocular complication occurred two years later, but remained stable thereafter. Both disorders remained stable during the subsequent eight years. Despite extensive and repeated instrumental and laboratory workout, only very limited immunological abnormalities were detected (besides the extremely low CD4+ lymphocyte count), and no apparent explaination was found for the disabling paraparesis syndrome. Idiopathic CD4+ lymphocytopenia, whose pathogenesis deserves careful investigation, has been associated with a very broad spectrum of signs and symptoms, ranging from negligible or no disturbances, to severe lymphoproliferative disorders, different opportunistic infections, and other focal diseases, including neurological pathologies. However, the association of a long-lasting profound peripheral CD4+ lymphocyte depletion in absence of any opportunistic infection or neoplasm, and isolated paraparesis and conjunctival microangiopathy, represents an absolutely unique finding, especially due to the apparently stable course of the above-mentioned syndrome.     

Altered Responses to Homeostatic Cytokines in Patients with Idiopathic CD4 Lymphocytopenia

Idiopathic CD4 lymphocytopenia (ICL) is a rare immune deficiency characterized by a protracted CD4⁺ T cell loss of unknown etiology and by the occurrence of opportunistic infections similar to those seen in AIDS. We investigated whether a defect in responses to cytokines that control CD4⁺ T cell homeostasis could play a role in ICL. Immunophenotype and signaling responses to interleukin-7 (IL-7), IL-2, and thymic stromal lymphopoietin (TSLP) were analyzed by flow cytometry in CD4⁺ T cells from 15 ICL patients and 15 healthy blood donors. The induction of phospho-STAT5 after IL-7 stimulation was decreased in memory CD4⁺ T cells of some ICL patients, which correlated with a decreased expression of the IL-7Rα receptor chain (R = 0.74, p<0.005) and with lower CD4⁺ T cell counts (R = 0.69, p<0.005). IL-2 responses were also impaired, both in the Treg and conventional memory subsets. Decreased IL-2 responses correlated with decreased IL-7 responses (R = 0.75, p<0.005), pointing to combined defects that may significantly perturb CD4⁺ T cell homeostasis in a subset of ICL patients. Unexpectedly, responses to the IL-7-related cytokine TSLP were increased in ICL patients, while they remained barely detectable in healthy controls. TSLP responses correlated inversely with IL-7 responses (R = −0.41; p<0.05), suggesting a cross-regulation between the two cytokine systems. In conclusion, IL-7 and IL-2 signaling are impaired in ICL, which may account for the loss of CD4⁺ T cell homeostasis. Increased TSLP responses point to a compensatory homeostatic mechanism that may mitigate defects in γc cytokine responses.     

Intestinal Parasitosis in Relation to Anti-Retroviral Therapy,CD4+ T-cell Count and Diarrhea in HIV Patients

Intestinal parasitic infections are one of the major causes of diarrhea in human immunodeficiency virus (HIV) seropositive individuals. Antiretroviral therapy has markedly reduced the incidence of many opportunistic infections, but parasite-related diarrhea still remains frequent and often underestimated especially in developing countries. The present hospital-based study was conducted to determine the spectrum of intestinal parasitosis in adult HIV/AIDS (acquired immunodeficiency syndrome) patients with or without diarrhea with the levels of CD4⁺ T-cell counts. A total of 400 individuals were enrolled and were screened for intestinal parasitosis. Of these study population, 200 were HIV seropositives, and the remaining 200 were HIV uninfected individuals with or without diarrhea. Intestinal parasites were identified by using microscopy as well as PCR assay. A total of 130 (32.5%) out of 400 patients were positive for any kinds of intestinal parasites. The cumulative number of parasite positive patients was 152 due to multiple infections. A significant association of Cryptosporidium (P<0.001) was detected among individuals with CD4⁺ T-cell counts less than 200 cells/μl.     

Why is HIV a pathogen?

The pathogenesis of HIV begins with a profound depletion of CD4+ T cells in the gut followed by a long period of clinically silent but dynamic virus replication and diversification with high host cell turnover before the onset of AIDS. The AIDS-defining opportunistic infections and tumors mark the end-point of a long balancing act between virus and host that occurs when CD4+ T cell numbers fall below a level that can sustain immunity. Comparative studies of lentivirus infections in other species show that AIDS is not an inevitable outcome of infection because simian immunodeficiency virus in natural hosts seldom causes disease. What distinguishes pathogenic from 'passenger' infection is a systemic activation of immune responses followed by destruction of the integrity of lymphoid follicles. Macrophage and dendritic cell infection also contribute to pathogenesis. Maedi-Visna virus infection in sheep, which targets these cells but not T lymphocytes, also leads to progressive disease and death that resembles the wasting and brain diseases of HIV without the T cell immunodeficiency. Thus, lessons from pathogenic and nonpathogenic lentivirus infections provide insight into the complex syndrome called AIDS.     

Probable disseminated Mycobacterium abscessus subspecies bolletii infection in a patient with idiopathic CD4+ T lymphocytopenia: a case report

ABSTRACT: INTRODUCTION: Rapidly growing mycobacteria are opportunistic pathogens in patients with underlying riskfactors. Mycobacterium abscessus subsp. bolletii is a newly recognized member of rapidlygrowing mycobacteria, isolated from respiratory tract and cutaneous infections. CASE PRESENTATION: We describe a case of chronic disseminated infection caused by M. abscessus subsp. bolletiiin a 38-year-old Sri Lankan man with idiopathic CD4+ T lymphocytopenia. Idiopathic CD4+T lymphocytopenia is a rare cause of immunodysfunction that, similar to humanimmunodeficiency virus infection. M. abscessus subsp. bolletii infection was diagnosed byculture isolation from two sputum samples. CONCLUSIONS: To the best of our knowledge this is the first report of M. abscessus subsp. bolletiidisseminated infection in a patient affected by idiopathic CD4+ T lymphocytopenia. Incontrast to previous reports, the isolate of M. abscessus subsp. bolletii presented intermediateresistance to clarithromycin and was susceptible to cefoxitin and imipenem.     

Derivation and characterization of a highly pathogenic isolate of human immunodeficiency virus type 2 that causes rapid CD4+ cell depletion in Macaca nemestrina

With few exceptions, humans are the only species known to develop acquired immunodeficiency syndrome (AIDS) after human immunodeficiency virus (HIV) infection. We report here that an isolate of HIV type 2, EHO, readily established persistent infection in 100% of Macaca nemestrina in three consecutive transmission studies. Of the eight infected animals, five showed persistently high virus load and six developed AIDS-like diseases or CD4+ cell depletion within 4 years of infection. The pathology and clinical signs closely parallel those of HIV-1 infection of humans, including lymphadenopathy, anemia, CD4+ cell depletion, and opportunistic infections. A cell-free virus stock was established from the lymph nodes of an animal that developed AIDS-like diseases. This virus, HIV-2/287, was highly pathogenic in M. nemestrina, causing CD4+ cell depletion within 2-8 weeks postinfection. While both HIV-2 EHO and HIV-2/287 use predominantly CXCR4, the latter shows greatly enhanced replicative capacity in macaque peripheral blood mononuclear cells (PBMCs). The establishment of a human immunodeficiency virus that causes rapid and reproducible CD4 cell depletion in macaques could facilitate the study of HIV pathogenesis and the development of effective vaccines and therapy against AIDS.     

Immunological memory and acquired immunodeficiency syndrome pathogenesis

Infection with the human immunodeficiency virus results in profound perturbations in immunological memory, ultimately resulting in increased susceptibility to opportunistic infections and acquired immunodeficiency syndrome (AIDS). We have used rhesus macaques infected with the simian immunodeficiency virus (SIV) as a model to understand better the effects of AIDS virus infection on immunological memory. Acute infection with SIV resulted in significant deficits in CD4+ helper responses to cytomegalovirus (CMV) as well as CMV-specific cytotoxic T-lymphocyte and neutralizing antibody responses. Reactivation of CMV was associated with high levels of SIV replication and suppression of both T-helper and cytotoxic responses to CMV. We have also studied the effects of SIV infection on T-cell turnover in non-human primates. T-cell turnover was evaluated using the nucleoside analogue bromodeoxyuridine (BrdU) in combination with five-colour flow cytometric analysis. T cells in normal animals turned over at relatively rapid rates, with memory cells turning over more quickly than naive cells. In SIV-infected animals, the labelling and elimination rates of both CD4+ and CD8+ BrdU-labelled cells were increased by two- to threefold compared with normal controls. Further analysis of immunological memory in non-human primates should offer the opportunity to extend immunological insights from murine models to the pathogenesis and prevention of AIDS.     

Derivation and characterization of a highly pathogenic isolate of human immunodeficiency virus type 2 that causes rapid CD4+ cell depletion in Macaca nemestrina

With few exceptions, humans are the only species known to develop acquired immunodeficiency syndrome (AIDS) after human immunodeficiency virus (HIV) infection. We report here that an isolate of HIV type 2, EHO, readily established persistent infection in 100% of Macaca nemestrina in three consecutive transmission studies. Of the eight infected animals, five showed persistently high virus load and six developed AIDS-like diseases or CD4⁺ cell depletion within 4 years of infection. The pathology and clinical signs closely parallel those of HIV-1 infection of humans, including lymphadenopathy, anemia, CD4⁺ cell depletion, and opportunistic infections. A cell-free virus stock was established from the lymph nodes of an animal that developed AIDS-like diseases. This virus, HIV-2/287, was highly pathogenic in M. nemestrina, causing CD4⁺ cell depletion within 2–8 weeks post-infection. While both HIV-2 EHO and HIV-2/287 use predominantly CXCR4, the latter shows greatly enhanced replicative capacity in macaque peripheral blood mononuclear cells (PBMCs). The establishment of a human immunodeficiency virus that causes rapid and reproducible CD4⁺ cell depletion in macaques could facilitate the study of HIV pathogenesis and the development of effective vaccines and therapy against AIDS.     

Gastrointestinal Viral Load and Enteroendocrine Cell Number Are Associated with Altered Survival in HIV-1 Infected Individuals

Human immunodeficiency virus type 1 (HIV-1) infects and destroys cells of the immune system leading to an overt immune deficiency known as HIV acquired immunodeficiency syndrome (HIV/AIDS). The gut associated lymphoid tissue is one of the major lymphoid tissues targeted by HIV-1, and is considered a reservoir for HIV-1 replication and of major importance in CD4+ T-cell depletion. In addition to immunodeficiency, HIV-1 infection also directly causes gastrointestinal (GI) dysfunction, also known as HIV enteropathy. This enteropathy can manifest itself as many pathological changes in the GI tract. The objective of this study was to determine the association of gut HIV-1 infection markers with long-term survival in a cohort of men who have sex with men (MSM) enrolled pre-HAART (Highly Active Antiretroviral Therapy). We examined survival over 15-years in a cohort of 42 HIV-infected cases: In addition to CD4+ T cell counts and HIV-1 plasma viral load, multiple gut compartment (duodenum and colon) biopsies were taken by endoscopy every 6 months during the initial 3-year period. HIV-1 was cultured from tissues and phenotyped and viral loads in the gut tissues were determined. Moreover, the tissues were subjected to an extensive assessment of enteroendocrine cell distribution and pathology. The collected data was used for survival analyses, which showed that patients with higher gut tissue viral load levels had a significantly worse survival prognosis. Moreover, lower numbers of serotonin (duodenum) and somatostatin (duodenum and colon) immunoreactive cell counts in the gut tissues of patients was associated with significant lower survival prognosis. Our study, suggested that HIV-1 pathogenesis and survival prognosis is associated with altered enteroendocrine cell numbers, which could point to a potential role for enteroendocrine function in HIV infection and pathogenesis.     

Natural variation in HIV infection: Monte Carlo estimates that include CD8 effector cells

Viral load and CD4 T-cell counts in patients infected with the human immunodeficiency virus (HIV) are commonly used to guide clinical decisions regarding drug therapy or to assess therapeutic outcomes in clinical trials. However, random fluctuations in these markers of infection can obscure clinically significant change. We employ a Monte Carlo simulation to investigate contributing factors in the expected variability in CD4 T-cell count and viral load due solely to the stochastic nature of HIV infection. The simulation includes processes that contribute to the variability in HIV infection including CD4 and CD8 T-cell population dynamics as well as T-cell activation and proliferation. The simulation results may reconcile the wide range of variabilities in viral load observed in clinical studies, by quantifying correlations between viral load measurements taken days or weeks apart. The sensitivity of variability in T-cell count and viral load to changes in the lifetimes of CD4 and CD8 T-cells is investigated, as well as the effects of drug therapy.     

The breakdown of the cytokine network subsequent to human immunodeficiency virus infection

The acquired immunodeflciency syndrome (AIDS) is a clinically multifaceted disease induced by infection with the human immunodeficiency virus (HIV). HIV infection results in a complex pattern of immunologic alterations that leads to the development of AIDS in the majority of HIV seropositive (HIV+) individuals. The reduction in CD4 T lymphocyte counts is the hallmark of HIV infection; nevertheless, long before the reduction in CD4 counts reaches critical levels, a series of profound and complex defects that impair the function of CD4 T lymphocytes can be detected. Thus, HIV infection is characterized by quantitative and qualitative defects affecting CD4 T lymphocytes. It was suggested recently that programmed cell death (PCD) is an important mechanism leading to CD4 depletion in HIV infection, and that susceptibility of peripheral lymphocytes to PCD is differentially regulated by diverse cytokines. Thus, type 1 cytokines would protect CD4 lymphocytes against PCD, whereas type 2 cytokines would not protect against, and could augment, PCD. We suggest that the qualitative alterations of the immune response provoke the CD4 depletion characteristic of HIV disease via type 2 cytokinemediated augmentation of PCD, and are therefore ultimately responsible for the progression of HIV infection. Finally, we summarize recent data showing that three correlates of disease progression: emergence of HIV strains with syncitium-inducing ability (SI), type 1-to-type 2 cytokine shift, and CD4 depletion, are significantly associated, suggesting a complex interconnected virologic-immunologic pathogenesis of HIV infection.     

Molecular pathogenesis of human immunodeficiency virus infection

Molecular studies of the pathogenesis of human immunodeficiency virus (HIV) infections have proceded rapidly following the molecular cloning and nucleotide sequence analysis of the HIV genome. Correlation of biochemical and functional studies of HIV-infected cells with the HIV nucleotide sequence has allowed the identification and preliminary functional characterization of many HIV proteins. These include structural proteins (gag), viral enzymes (pol), and viral regulatory proteins (tat, art). Cloned HIV DNA segments have been utilized as probes for in situ nucleic acid hybridization to study the distribution of HIV-infected cells in acquired immunodeficiency syndrome (AIDS) and AIDS-related complex (ARC) patients. These studies have demonstrated the infection of macrophages as an important component of HIV-induced neurologic disease. Only very low numbers of HIV-infected lymphocytes can be identified in the peripheral blood of infected individuals. Thus, the mechanism of CD4 cell depletion in the pathogenesis of AIDS remain obscure.     

The value of primate models for studying human immunodeficiency virus pathogenesis

Abstract: Research on human immunodeficiency virus (HIV) infection is compromised by the obvious limitation in having for study only virus-infected individuals or those exposed to the virus. Steps involved in transmission or pathogenesis require planned experimentation. The identification of animal models of acquired immunodeficiency syndrome (AIDS) has therefore been helpful for evaluating phases of HIV pathogenesis. Of the seven subgenera of lentiviruses now recognized, two share the characteristics with HIV of a T cell tropism and the associated loss of CD4+ cells in the host associated with disease: the feline immunodeficiency virus (FIV) and the simian immunodeficiency virus (SIV) (Table 1). The other animal lentiviruses grow best in macrophages and their infection generally reflects clinical sequellae of infection of this cell type. This review addresses those features of SIV, HIV, and SHIV infections of non-human primates that illustrate the importance of the animal models of AIDS.     

Synthesis and antiretroviral activity of phospholipid analogs of azidothymidine and other antiviral nucleosides

Treatment of acquired immunodeficiency syndrome with azidothymidine (AZT, zidovudine) reduces p24 antigenemia, increases CD4 lymphocyte counts, reduces the frequency and severity of opportunistic infections and prolongs life. However, AZT and other dideoxynucleosides do not diminish the ability to isolate human immunodeficiency virus (HIV) from peripheral blood mononuclear cells. Failure to clear infectious virus may be due to inadequate inhibition of virus production by macrophages, a major reservoir of HIV infection. Cells of the macrophage lineage take up large amounts of parenterally administered liposomal material. To direct larger proportions of antiretroviral nucleosides to this important HIV reservoir, we synthesized phosphatidylAZT, AZT diphosphate dipalmitin, phosphatidylddC and phosphatidylddT, novel phospholipid prodrugs which are readily incorporated into phospholipid bilayers. These liposomal liponucleotides were shown to have antiretroviral activity in HIV-infected U937 and CEM cells. In vivo, it is anticipated that liposomes containing the antiretroviral liponucleotides will be taken up in large proportion by macrophages. This property would appear to make phosphatidylAZT and the related compounds promising candidate agents with a special potential to target drug to the macrophage reservoir of HIV infection, thereby reducing the toxicity of the antiviral nucleosides to other cells.     

Frequency and Absolute Number of FoxP3^＋ Regulatory T Cells Correlate with Disease Progression of Chronic HIV-1 Infection

CD4 CD25 Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However,whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue,we enumerated the Treg absolute counts and frequency in 75 antiviral-nave HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition,with disease progression indicated by CD4 T-cell absolute counts,circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased,suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection. Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus,our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection,influencing the disease progression.     

Frequency and Absolute Number of FoxP3+ Regulatory T Cells Correlate with Disease Progression of Chronic HIV-1 Infection

CD4+CD25+ Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However, whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue, we enumerated the Treg absolute counts and frequency in 75 antiviral-na(i)ve HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition, with disease progression indicated by CD4 T-cell absolute counts, circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased, suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection.Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus, our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection,influencing the disease progression.     

Frequency and absolute number of FoxP3<Superscript>+</Superscript> regulatory T cells correlate with disease progression of chronic HIV-1 infection

CD4⁺CD25⁺ Regulatory T cells (Treg) have been found to down-regulate immune activation in HIV-1 infection. However, whether the depletion of Treg benefits to the disease status of HIV infection remains undefined. To address this issue, we enumerated the Treg absolute counts and frequency in 75 antiviral-naïve HIV-1-infected individuals in this study. It was found that HIV-infected patients displayed a significant decline in Treg absolute counts but a significant increase in Treg frequency. In addition, with disease progression indicated by CD4 T-cell absolute counts, circulating Treg frequency gradually increased; while Treg absolute counts were gradually decreased, suggesting that the alteration of Treg number closely correlated with disease progression in HIV infection. Functional analysis further showed that Treg efficiently inhibit both CD4 and CD8 T cell proliferation in vitro. Thus, our findings indicates that Treg actively participate in pathogenesis of chronic HIV infection, influencing the disease progression.