Dendritic cells and differential usage of the MHC class II transactivator promoters in the central nervous system in experimental autoimmune encephalitis

In the normal central nervous system (CNS) expression of MHC class II is mi nimal, but has been found to be highly up-regulated on microglia cells in e xperimental autoimmune encephalitis (EAE). Here we used the EAE model to ex amine the regulation of expression of the class II transactivator (CIITA), which is required for activation of MHC class II genes. EAE was induced in C57BL/6 mice by immunization with myelin oligodendrocyte glycoprotein pepti de 35-55. CIITA mRNA form I (specific for dendritic cells) and form IV (IFN -gamma inducible) but not form III (B cell specific) were detected in brain and spinal cord of mice with acute EAE. In unimmunized or mock-immunized m ice, none of the three CIITA forms was found to be induced. Dendritic cells (DC) were identified by immunostainings for CD11c in perivascular and meni ngeal cell infiltrates in EAE spinal cord and brain. Time-course analysis s howed (1) the appearance of DC in the CNS shortly before onset of disease, (2) the recruitment of CD11b(+) cells occuring much earlier and (3) the abs ence of CIITA and MHC class II expression in these CD11b(+) cells at precli nical stages.