HUMAN IL-10 REDUCES THE NUMBER OF IL-4-INDUCED IGE B-CELLS IN CULTURES OF ATOPIC MONONUCLEAR-CELLS

We investigated the effect of recombinant human IL-10 on IL-4- and ant igen-driven human peripheral blood mononuclear cell cultures derived f rom atopic donors. These cultures were phenotyped for the percentage o f B cell (CD20 HLA-DR) population by flow cytometry and for intracellu lar IgE using epifluorescence microscopy. The addition of IL-4 (100 U/ ml) to these cultures resulted in an increase in the percentage of IgE B cells. However, the percentage of IgE B cells in cultures coincubat ed with IL-10 (2 or 20 ng/ml) and IL-4 was reduced to the level of med ium control. Peripheral-blood mononuclear (PBMN) cultures driven with dust mite allergen demonstrated a significant increase in cellular pro liferation, as measured by (3)[H] thymidine uptake, and in the percent age of IgE B cells. The coaddition of IL-10 (2 or 20 ng/ml) to these c ultures significantly inhibited both proliferation and the mean percen tage of IgE B cells. The inhibitory effect of IL-10 on IgE B cell perc entages in both the IL-4- and the allergen-driven cultures, and on all ergen-driven proliferation, was dependent upon the presence of monocyt es. Interestingly, the inhibitory effect of IL-10 on allergen-driven p roliferation in the atopic PBMN cultures was reversible by the coaddit ion of exogenous IFN gamma (1 ng/ml) and IL-2 (2 U/ml). The addition o f IL-2 (2 U/ml) partially reversed IL-10-inhibited allergen-driven pro liferation while alone IFN gamma had no effect (1 ng/ml). In fact, the addition of IFN gamma (1 ng/ml) in the absence of either IL-10 or IL- 2 (2 U/ml) partially inhibited allergen-driven proliferation. Yet, exo genous IFN gamma (1 ng/ml) induced the expression of monocyte cell sur face HLA-DR in the presence of inhibitory levels of IL-10. IL-2 (2 U/m l) did not replete monocyte HLA-DR expression that was inhibited by IL -10. Finally, monocyte expression for surface CD14 was observed to inc rease with IL-10 treatment and to decrease under conditions of allerge n-induced proliferation. Monocyte CD14 expression by IL-10 appeared to be indirect, i.e. by the suppression of IFN gamma, from T cells. The expression of monocyte HLA-DR coupled with the loss of expression for monocyte CD14 in the presence of IL-2 was sufficient to overcome IL-10 inhibition of allergen-driven proliferation. A possible mechanism for IL-10 inhibition is discussed.