B-1 cells are the predominant B cells to foster latent infection in the peritoneal cavity and are subdivided into B-1a (CD5 neg) and B-1b (CD5 pos) cells based on CD5 expression, with B-1b cells harboring most, if not all, of the latent MHV68 compared to B-1a cells (59, 60). This evidence concerns the gene CD5 and disease arising from reactivation of latent virus.