Contribution of CD8+ T cells to containment of viral replication and emergence of mutations in Mamu-A*01-restricted epitopes in Simian immunodeficiency virus-infected rhesus monkeys.

Here, we investigated the containment of virus replication in simian immunodeficiency virus (SIV) infection by CD8(+) lymphocytes. Escape mutations in Mamu-A*01 epitopes appeared first in SIV Tat TL8 and then in SIV Gag p11C. The appearance of escape mutations in SIV Gag p11C was coincident with compensatory changes outside of the epitope. Eliminating CD8(+) lymphocytes from rhesus monkeys during primary infection resulted in more rapid disease progression that was associated with preservation of canonical epitopes. These results confirm the importance of cytotoxic T cells in controlling viremia and the constraint on epitope sequences that require compensatory changes to go to fixation.

Chronic Systemic Immune Dysfunction in African-Americans with Small Vessel-Type Ischemic Stroke.

The incidence of small vessel-type (lacunar) ischemic strokes is greater in African-Americans compared to whites. The chronic inflammatory changes that result from lacunar stroke are poorly understood. To elucidate these changes, we measured serum inflammatory and thrombotic biomarkers in African-Americans at least 6 weeks post-stroke compared to control individuals. Cases were African-Americans with lacunar stroke (n = 30), and controls were age-matched African-Americans with no history of stroke or other major neurologic disease (n = 37). Blood was obtained >6 weeks post-stroke and was analyzed for inflammatory biomarkers. Freshly isolated peripheral blood mononuclear cells were stimulated with lipopolysaccharide (LPS) to assess immune responsiveness in a subset of cases (n = 5) and controls (n = 4). After adjustment for covariates, the pro-inflammatory biomarkers, soluble vascular cadherin adhesion molecule-1 (sVCAM-1) and thrombin anti-thrombin (TAT), were independently associated with lacunar stroke. Immune responsiveness to LPS challenge was abnormal in cases compared to controls. African-Americans with lacunar stroke had elevated blood levels of VCAM-1 and TAT and an abnormal response to acute immune challenge >6 weeks post-stroke, suggesting a chronically compromised systemic inflammatory response.

Induction in mice of anti-Tat mucosal immunity by the intranasal and oral routes.

Anti-Tat vaccination experiments were carried out in mice with a view to inducing systemic in addition to mucosal immunity. For this, three types of immunizing preparations were tested, which consisted of Tat toxoid embedded in either an adjuvant oily structure (IMS), or nanoparticles of chitosan, or microparticles of polylactide-co-glycolide (PLG). Administered by either the intranasal or oral route all preparations triggered anti-Tat IgG and IgA antibodies. Sera from mice immunized with either of these preparations could also inhibit significantly the Tat transactivating activity. These results open up a new avenue to the development of an effective anti-AIDS protective vaccine.

Antiretroviral therapy does not block the secretion of the human immunodeficiency virus tat protein.

Tat is a viral protein secreted from HIV infected cells and extra cellular Tat is suspected to prevent destruction of HIV infected cells from cells of the cellular immunity. The effect of anti retroviral therapy (ART) on Tat secretion has never been investigated. In this study, we tested for antibody reactivity against Tat variants representative of the main HIV subtypes in HIV positive patients receiving ART with undetectable viral loads ( < 40 copies/mL) over the course of one year with a blood sampling every three months. For each of theses five blood sampling, an average of 50 % of patients had Anti-Tat IgG, it turned out that 86% of patients could recognize Tat at least in one blood sampling during the course of the study. Amazingly, anti-Tat IgG appeared and/or disappeared in 66 % of patients. Only 20% had anti-Tat IgG remaining persistently while 14% were consistently without anti Tat IgG in the five blood sampling. No significant correlation was found between anti-Tat IgG and CD4+ T cell, CD8+ T cell and B cell counts revealing the incapacity of these anti Tat IgG to neutralize extra cellular Tat. Interestingly the absence and then the appearance of anti-Tat IgG in patients suggest the presence of HIV infected cells in the blood that may constitute a significant reservoir of HIV infected cells. As a conclusion antiretroviral therapy does not block the secretion of Tat and may explain why HIV infected cells can survive in spite of an effective ART treatment.

High-performance capillary electrophoresis for determining HIV-1 Tat protein in neurons.

The HIV-1 protein, Tat has been implicated in AIDS pathogenesis however, the amount of circulating Tat is believed to be very low and its quantification has been difficult. We performed the quantification of Tat released from infected cells and taken up by neurons using high performance capillary electrophoresis. This is the first report to successfully measure the amount of Tat in neurons and places Tat as a key player involved in HIV-associated neurocognitive disorders.

Sensitization of T cells to CD95-mediated apoptosis by HIV-1 Tat and gp120.

The depletion of CD4+ T cells in AIDS is correlated with high turnover of the human immunodeficiency virus HIV-1 and associated with apoptosis. The molecular mechanism of apoptosis in HIV infection, however, is largely unknown. T-cell apoptosis might be affected by viral proteins such as HIV-1 Tat and gp120 (refs 10, 11). T-cell-receptor (TCR)-induced apoptosis was recently shown to involve the CD95 (APO-1/Fas) receptor. We show here that HIV-1 Tat strongly sensitizes TCR- and CD4(gp120)-induced apoptosis by upregulation of CD95 ligand expression. Concentrations of Tat found to be effective in cultures of HIV-1-infected cells were also observed in sera from HIV-1-infected individuals. Taken together, our results indicate that HIV-1 Tat and gp120 accelerate CD95-mediated, activation-induced T-cell apoptosis, a mechanism that may contribute to CD4+ T-cell depletion in AIDS.

Tat-associated kinase, TAK, activity is regulated by distinct mechanisms in peripheral blood lymphocytes and promonocytic cell lines.

TAK, a multisubunit cellular protein kinase that specifically associates with the human immunodeficiency virus Tat proteins and hyperphosphorylates the carboxyl-terminal domain of RNA polymerase II, is a cofactor for Tat and mediates its transactivation function. The catalytic subunit of TAK has been identified as cyclin-dependent kinase Cdk9, and its regulatory partner has been identified as cyclin T1; these proteins are also components of positive transcription elongation factor P-TEFb. TAK activity is up-regulated upon activation of peripheral blood lymphocytes and following macrophage differentiation of promonocytic cell lines. We have found that activation of peripheral blood lymphocytes results in increased mRNA and protein levels of both Cdk9 and cyclin T1. Cdk9 and cyclin T1 induction occurred in purified CD4(+) primary T cells activated by a variety of stimuli. In contrast, phorbol ester-induced differentiation of promonocytic cell lines into macrophage-like cells produced a large induction of cyclin T1 protein expression from nearly undetectable levels, while Cdk9 protein levels remained at a constant high level. Measurements of cyclin T1 mRNA levels in a promonocytic cell line suggested that regulation of cyclin T1 occurs at a posttranscriptional level. These results suggest that cyclin T1 and TAK function may be required in differentiated monocytes and further show that TAK activity can be regulated by distinct mechanisms in different cell types.