DIFFERENTIAL-EFFECTS OF INTERLEUKIN-10 ON THE EXPRESSION OF HLA CLASS-II AND CD1 MOLECULES INDUCED BY GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR INTERLEUKIN-4

Interleukin (IL)-10 down-regulates HLA class II molecules, whether constitutively expressed or up-regulated by interferon-gamma or IL-4 on monocytes but not on B lymphocytes. In this study we show that IL-10 does not inhibit HLA class II expression induced by the combination granulocyte/macrophage colony-stimulating factor and IL-4 on monocytes, although it simultaneously abrogates the expression of CD1 molecules induced by the same combination of cytokines. CD1 molecules can act as element of genetic restriction for CD4(-)CD8(-)T lymphocytes, and the suppression of CD1 expression by IL-10 abolished antigen presentation to CD1-restricted CD4(-) CD8(-) T cell receptor-positive T cells. Although HLA class II expression was not down-regulated by IL-10, the antigen specific proliferative response of CD4(+) T cells was nevertheless decreased. This was not caused by down-regulation of known co-stimulatory molecules such as B7.1, B7.2 and ICAM-1. IL-10 decreased the antigen specific proliferative response further by directly influencing the T lymphocytes. Our results indicate that IL-10 exerts some of its immunoregulatory functions by differential modulation of antigen presenting molecules, induced by the same combination of cytokines.