ENCAPSULATION OF CRYPTOCOCCUS-NEOFORMANS WITH GLUCURONOXYLOMANNAN INHIBITS THE ANTIGEN-PRESENTING CAPACITY OF MONOCYTES

This report examines the effect of the major capsular polysaccharide o f Cryptococcus neoformans, glucuronoxylomannan (GXM), on the antigen-p resenting capability of human monocytes treated with acapsular cells o f C, neoformans, We found that pretreatment of acapsular cryptococci w ith GXM downregulates, in a dose-dependent manner, the antigen-present ing capacity of monocytes, leading to reduced proliferative T-lymphocy te responses, Similar levels of suppression occurred when monocytes we re exposed to encapsulated cryptococci or acapsular cryptococci that w ere pretreated with GXM, The magnitude of the T-cell response correlat ed with the ability of monocytes to ingest the yeast. Supernatant flui ds from cocultures of monocytes and T cells cultured with encapsulated cryptococci contained higher levels of interleukin-10 (IL-10) than su pernatant fluids of cells with acapsular cryptococci, Addition of anti -IL-10 monoclonal antibodies to the incubation medium of monocytes and T cells cultured with encapsulated cryptococci restored proliferative T-cell responses to levels observed during culture with acapsular cry ptococci, Finally, treatment of monocytes with encapsulated cryptococc i or GXM-treated acapsular cryptococci suppressed expression of class Il major histocompatibility complex (MHC) molecules in a manner consis tent with previous reports of IL-10-mediated suppression of class II M HC molecules and suppression of proliferative T-cell responses, These results suggest a link between GXM encapsulation, increased IL-10 synt hesis by monocytes, decreased expression of class II MHC molecules on monocytes, and reduced proliferative T-cell responses.