HUMAN MICROGLIA ACTIVATE LYMPHOPROLIFERATIVE RESPONSES TO RECALL VIRAL-ANTIGENS

The capacity of adult human microglia to activate memory T-lymphocyte responses to recall viral antigens in autologous peripheral blood lymp hocytes (PBL) was examined using measles and influenza viruses. Microg lia and peripheral blood macrophages were isolated from 6 patients who underwent surgical brain biopsies. Microglial cultures readily expres sed high levels of HLA class II molecules under basal culture conditio ns. However, compared to macrophages, microglia appeared to express mu ch lower levels of CD45, a phenotype that has been associated with the ability of rat brain macrophage/microglia to present antigen. PBL wer e depleted of macrophages (D-PBL) and the efficacy of the depletion wa s assessed by a reduction in the T-cell response to concanavalin A. D- PBL were reconstituted with macrophages, microglia, or in some cases m icroglia pretreated with interferon-gamma (IFN gamma). It was observed that microglia were as efficient as macrophages in presenting viral a ntigens, Pretreatment of microglia with IFN gamma did not enhance furt her antigen presentation. Oligodendrocytes which lack constitutive or inducible HLA class II molecules failed to present viral antigens. The results have implications on the direct function of microglia as perp etuators and possibly initiators of immune responses to virus infectio n in the central nervous system compartment.