Primary infection with HIV results in an acute HIV syndrome associated with high level of viremia, followed by a clinical latent period and culminating in AIDS. One paradox of HIV disease involves the immune suppression even with normal CD4+ T cell numbers. Several immunogenetic mechanisms have been postulated for the dysfunction of CD4+ T cells. Regulatory proteins of HIV-1 play a significant role in viral replication. In addition to their influences in regulation of HIV gene expression, several investigator have demonstrated that exogenous tat proteins can profoundly influence cellular functions. I have investigated the effect of the regulatory proteins if HIV, tat, nef and vif on normal T cell function. CD4+ tetanus and PPD-antigen-specific, exogenous IL-2 independent T cell clones pretreated with synthetic tat peptide, but not recombinant nef or vif proteins were inhibited in their ability to proliferate and secrete interleukin 2. Treatment of T cell clones with tat peptide did ont affect antigen-induced increase in tricellular calcium, hydrolysis of phosphatidyl inositol to inositol triphosphate, or translocation of protein kinase C from cytosol to membrane. Thus the nature of the intracytoplasmic defects ensuing from tat-induced inhibitory responses still remains obscure. The central hypothesis of this proposal is that HIV-tat can profoundly influence the intracytoplasmic signalling mechanisms of T lymphocytes, which could result in a qualitative decline of CD4+ T cell functions, prior to the depletion of CD4+ T cell numbers. A detailed examination of the effects of tat on the signal transduction events following CD3/TCR-mediated T cell activation is being proposed, utilizing state of the art technologies and concepts of T cell activation. The novel concept in this proposal involves dissection of TCR-induced signalling pathways resulting in IL-2 secretion, that does not block the classical phospholipase C r1 (PLCr1)-induced PI hydrolysis, but inhibits IL-2 secretion. Preliminary studies have indicated that treatment of peripheral blood T cells with tat protein transiently downmodulates expression of the CD45 molecule on peripheral blood T lymphocytes. This proposal will analyze whether tat affects the CD45-associated phosphatase activity, a key molecule in the TCR-induced T cell signalling. All of the studies will be conducted in a prototype """"""""physiologic"""""""" system, utilizing antigen-specific T cell clones. Studies will also be conducted to identify the inhibitory region(s) of tat utilizing short synthetic peptides, and the use of anti-sense oligonucleotide technology. The proposed investigation is important in gaining an insight into the mechanism of the action of tat, the immunopathogenesis of AIDS, particularly in qualitative defects of CD4+ T cell function and also has implications in the use of therapeutic agents utilizing inhibitors of tat-induced HIV gene regulation.
| Chirmule, N; Avots, A; LakshmiTamma, S M et al. (1999) CD4-mediated signals induce T cell dysfunction in vivo. J Immunol 163:644-9 |
