Human CD4-reactive antibodies from SLE patients induce reversible inhibition of polyclonal T lymphocyte proliferation

Anti-CD4 antibodies in exposed seronegative adults and in newborns of HIV type 1-seropositive mothers: a follow-up study

In this work, an ELISA for the quantitative determination of IgG anti-CD4 autoantibodies was validated and utilized in the follow-up of two cohorts of HIV-1-exposed seronegative subjects. A serum with an arbitrarily assigned concentration of 100,000 units/ml was used as a reference, and the detection limit, inter- and intraassay variability, and analytical recovery were calculated. The study subjects included adults sexually exposed to HIV-1-infected partners and the newborns of HIV-1+ mothers who seroreverted by 18 months of age. Some of these individuals were studied over an 18- to 24-month period. The detection limit of the assay was 2000 AU/ml. Intra- and interassay variability was, respectively, 3.92 and 3.90%. Analytical recovery in an assay in which a fixed amount of anti-CD4 antibodies was added to different samples was 98%. A proportion of adults (16 of 47, 34.0%) and babies (12 of 27, 44.4%) had significantly higher concentrations of anti-CD4 antibodies. Among them, 8 adults maintained the same concentration as that found in the first determination; on the other hand, 12 babies born to seronegative mothers showed a significant increase in the concentration of anti-CD4 antibodies during their first months of life. In conclusion, anti-CD4 antibodies can be measured using a validated ELISA. They represent a serologic trait that is quantitatively conserved in HIV-1-exposed seronegative adult individuals and is actively acquired by newborns to HIV+ mothers.

CD4 regulates susceptibility to Fas ligand- and tumor necrosis factor-mediated apoptosis

The current knowledge of CD4 function is limited to its role as a necessary coreceptor in TCR-initiated signaling. We have investigated whether CD4 regulates additional T cell functions. Using human primary resting CD4+ T cells, we demonstrate that CD4 activation is sufficient to induce lymphocyte death. Immediately after CD4 cross-linking, CD4+ T cells are rendered susceptible to apoptosis mediated by TNF or FasL. This, together with the concomitant induction of FasL within the same population, results in significant CD4+ T cell death in vitro. The CD4-dependent induction of susceptibility to apoptosis that is mediated by TNF or FasL is protein synthesis independent but phosphorylation dependent. After CD4 activation, PKC regulates susceptibility to apoptosis mediated by FasL but not the induction of susceptibility to TNF-dependent apoptosis. Moreover, significant differences between CD3 and CD4 activation were observed with regards to the kinetics of induction of CD4+ T cell susceptibility to FasL- and TNF-mediated apoptosis. Altogether, these results provide a model with which to study the molecular mechanisms regulating lymphocyte survival after CD4 activation, and highlight the potential role of CD4 in controlling lymphocyte apoptosis under physiological conditions or in disease states such as HIV infection.