The T cell receptor and AIDS pathogenesis

CD8+ lymphocyte-mediated injury of dorsal root ganglion neurons during lentivirus infection: CD154-dependent cell contact neurotoxicity

Neuronal damage in dorsal root ganglia (DRGs) with accompanying axonal injury is a key feature of human immunodeficiency virus (HIV)-related distal sensory polyneuropathy (DSP). In a model of HIV-related DSP, we observed numerous CD3+ T lymphocytes (p < 0.05) in DRGs from feline immunodeficiency virus (FIV)-infected animals, which also exhibited low CD4+ and high CD8+ lymphocyte levels in blood accompanied by a selective loss of small-diameter sural nerve axons (p < 0.05). FIV-infected lymphocytes cocultured with syngeneic DRGs caused neuronal damage, indicated by neurite retraction, neuronal soma atrophy, and loss (p < 0.05). In contrast, supernatants from FIV-infected or uninfected lymphocytes were minimally neurotoxic, despite high FIV virion levels. Among lymphocyte subsets cocultured with DRG cultures, CD8+ T cells from both FIV-infected and uninfected lymphocytes selectively caused DRG neuronal injury (p < 0.05). FIV-infected CD8+ T cells showed markedly increased CD154 expression (p < 0.05), whereas neurons were the predominant cells expressing CD40 in DRGs. Blocking CD154 on activated CD8+ T cells protected DRG neurons (p < 0.05). These findings indicated that CD8+ T cells were principal effectors of DRG neuronal injury after FIV infection through a CD40-CD154 interaction in a cell contact-dependent manner.

Oligoclonal T cells are infiltrating the brains of children with AIDS: sequence analysis reveals high proportions of identical beta-chain T-cell receptor transcripts

We have recently described the presence of perivascular CD3+ CD45RO+ T cells infiltrating the brains of children with AIDS. To determine whether these infiltrates contain oligoclonal populations of T cells, we amplified by PCR beta-chain T-cell receptor (TCR) transcripts from autopsy brains of four paediatric patients with AIDS. The amplified transcripts were cloned and sequenced. Sequence analysis of the beta-chain TCR transcripts from all four patients revealed multiple identical copies of TCR beta-chain transcripts, suggesting the presence of oligoclonal populations of T-cells. These TCR transcripts were novel. The presence of oligoclonal populations of T cells in the brains of these four paediatric patients with AIDS suggests that these T cells have undergone antigen-driven proliferation and clonal expansion very likely in situ, in the brains of these AIDS patients, in response to viral or self-antigens. Although the specificity of the clonally expanded beta-chain TCR transcripts remains to be elucidated, none of the beta-chain TCR transcripts identified in this study were identical to those specific for HIV-1 antigens that are currently reported in the GENBANK/EMBL databases. Certain common CDR3 motifs were observed in brain-infiltrating T cells within and between certain patients. Large proportions (24 of 61; 39%) of beta-chain TCR clones from one patient (NP95-73) and 2 of 27 (7%) of another patient (NP95-184-O) exhibited substantial CDR3 homology to myelin basic protein (MBP)-specific TCR derived from normal donors or TCR expressed in the brain of patients with multiple sclerosis (MS) or with viral encephalitis. These two patients (NP95-73 and NP95-184-O) also shared HLA class II with the normal donors and the MS patients who expressed these homologous TCR. Pathologic examination at autopsy of the brains revealed the presence of myelin pallor only in patient NP95-73. T-cell clones identified in the brain of patients NP95-73 and NP95-184-O may recognize MBP or another CNS self antigen and this recognition may be restricted by either DRB1*15 or DQB1*0602 specificities.

Sexual dimorphism in immune function: the role of prenatal exposure to androgens and estrogens

Perinatal exposure to androgens permanently transforms certain tissues, e.g., the brain, the genitalia, etc. This process involves both masculinization and defeminization. Immune function also is transformed by early steroid exposure; however, it is not yet known whether the response capabilities of the immunocytes themselves are directly modified or whether they are responding to signals from other masculinized tissues, e.g., the brain. Most evidence points to a direct effect since androgen and estrogen receptors are present in developing immunocytes. Both androgens and estrogens have a role in regulating adult immunity including Th1/Th2 balance. Adult susceptibility to autoimmune and other diseases is also related to steroid exposure. How immune cells respond to gonadal steroids in adulthood may depend on the pattern of androgenic and estrogenic stimulation during early development.

Does AIDS emerge from a disequilibrium between two complementary groups of molecules that mimic MHC?

There is increasing evidence that a disturbance of self-nonself-recognition plays an important role in the immunopathogenesis of AIDS. Here, Caner Susal, Volker Daniel and Gerhard Opelz speculate that the immune system is balanced between two groups of molecules that mimic major histocompatibility complex (MHC) proteins; AIDS is suggested to emerge as a consequence of human immunodeficiency virus (HIV) disturbing this balance in favor of anti-MHC class II responses.

Similar abnormalities of idiotype and immunoglobulin light chain expression and of cell-mediated cytotoxicity in HIV-infected humans and simian immunodeficiency virus (SIV)-infected rhesus macaques

The pathogenesis of AIDS in simian immunodeficiency virus (SIV)-infected rhesus macaques models the pathogenesis of human AIDS. We investigated whether certain immunological abnormalities associated with HIV infection and implicated in disease progression also occur in SIV infection. We observed striking parallels between the rhesus macaque humoral immune response to SIV and unusual features of the human humoral immune response to HIV infection. Anti-SIV envelope antibodies from SIV-infected macaques exhibited skewed kappa/lambda L chain usage relative to the ratio of kappa/lambda L chain usage detected on total plasma Ig. In addition, the same idiotope conserved on human anti-HIV gag, pol and env antibodies was detected with a similar distribution pattern on macaque anti-SIV env, gag and pol antibodies. Skewed Ig L chain representation and selection of a highly conserved possible dominant regulatory idiotope on antibodies against key neutralizing antigens raise the possibility that the progressive failure of the humoral immune response to SIV and HIV involves skewed oligoclonal humoral immunity. We also found that SIV-infected macaques, like HIV-infected humans, have elevated levels of CD8+ lymphocyte-mediated cytotoxicity. Cytotoxicity against human B cells was higher in CD8+ effector lymphocytes from SIV-infected macaques than in those from uninfected macaques (P < 0.05). Cell-mediated cytotoxicity against human NK cell targets was not elevated in effector lymphocytes from the SIV-infected macaques, suggesting that CTL activity was selectively elevated. Two out of seven SIV-infected macaques tested had CD8+ cytotoxic lymphocytes that selectively killed activated uninfected CD4+ macaque lymphocytes. Oligoclonal B cell responses and persistently elevated CD8+ lymphocyte-mediated cytotoxicity are consistent features of primate retroviral infections leading to AIDS. Understanding immune predispositions to these features triggered by HIV and SIV may advance new prophylactic and therapeutic strategies.