Interleukin‐dependent modulation of HLA‐DR expression on CD4 and CD8 activated T cells

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Abstract
Interleukins (IL) regulate differentT‐cell surface Ag known as activation markers that have distinct functional roles. In this paper, while studying the influence of some cytokines(IL‐12, IL‐2 and IL‐4) on the expression of several markers [CD69,CD25, CD26, CD3, human leukocyte antigen (HLA‐DR), CD45R0] in in vitro activated human T lymphocytes, we observed two groups of donors responding to phytohaemagglutinin (PHA) activation with high or low HLA‐DRAg expression. We also found that CD4 and CD8 populations had different HLA‐DR densities under PHA activation (particularly the high HLA‐DR‐expressing group). Interleukins, in a dose‐dependent manner (IL‐2 partially), upregulated these HLA‐DR levels. In 5 day cultures, IL‐12and IL‐2 enhanced the CD8/CD4 ratio of activated T cells, which was responsible, in part, for the IL‐dependent HLA‐DR upregulation. IL‐12 and IL‐2 also upregulated the HLA‐DR expression at the molecular level on CD8, and IL‐12 downregulated it on CD4 cells. It seems that IL‐4 upregulated HLA‐DR by shortening the mitogen‐dependent regulation kinetics. We hypothesize that the different effect of each IL on HLA‐DR expression might be related to the regulation of the dose of antigenic peptide presentation and, thus, also influence TH1/TH2 dominance.