To determine whether CNS-infiltrating myeloid cells, comprising macrophages and dendritic cells, and/or microglia are capable of processing and presenting self-Ag within the CNS following infection, both potential APC populations were purified based on differential CD45 expression [44, 45] at distinct times p.i. and tested for the ability to support SR T cell activation in the absence of exogenously added Ag. This evidence concerns the gene PTPRC and infection.