Antigen presentation by human monocytes: effects of modifying major histocompatibility complex class II antigen...

Lymphocyte proliferation in response to monocytes pulsed with an antigenic extract of Candida albicans was measured in vitro and the effects of modifying major histocompatibility complex (MHC) class II antigen expression at the surface of the antigen-presenting cells was investigated. The study shows that no simple correlation exists between changes in MHC class II antigen expression and changes in the effectiveness of antigen presentation. Recombinant interferon-alpha 1 (rIFN-alpha 1), rIFN-gamma and hydrocortisone were found to increase the expression of monocyte class II MHC antigens. In contrast, rIFN-alpha 2 did not increase class II antigen expression although it did increase MHC class I expression. Treatment of monocytes with rIFN-alpha 1, rIFN-alpha 2 or corticosteroids during antigen pulsing resulted in a reduction in the subsequent proliferative lymphocyte response. In all cases this inhibitory effect was restricted to antigen-specific proliferative responses since the polyclonal lymphocyte response to pokeweed mitogen-pulsed monocytes remained unaffected. Only rIFN-gamma treatment of antigen-pulsed monocytes resulted in enhancement of the subsequent specific lymphocyte proliferative response. The suppressive effects of hydrocortisone could not be attributed to its well documented inhibitory effects on arachidonic acid metabolism. The effect of C. albicans antigen, IFN and corticosteroids on interleukin 1 (IL 1) production by monocytes was also investigated. C. albicans antigen alone induced IL 1 production. So too did IFN-alpha 1 and IFN-gamma. IFN-alpha 2 did not induce IL 1 production. Addition of interferons together with C. albicans, however, resulted in the same level of IL 1 productions as with C. albicans antigen alone. Neither antigen nor IFN had any effect on IL 1 action in the thymocyte assay. Corticosteroids did not affect IL 1 production by monocytes but were potent antagonists of IL 1 in the thymocyte proliferation assay. Mitogen-induced thymocyte proliferation was also inhibited by corticosteroids. Pretreatment of monocytes with hydrocortisone followed by washing did not markedly affect their subsequent ability to produce IL 1 neither was it possible to reverse the inhibitory effects of hydrocortisone on antigen presentation by addition of exogenous IL 1. Thus, signals which alter class II MHC antigen expression influence the antigen-presenting capacity of monocytes by a mechanism independent of IL 1. No simple correlation exists between class II expression and antigen-presenting capacity.