The genes overexpressed in MS DP memB cells include CD80, a T cell costimulatory molecule that is increased in B cells by B cell activating stimuli, GM-CSF, and disease activity, and functions to greatly augment T cell activation (10, 59, 60), although whether the increased CD80 mRNA translates into greater CD80 surface protein expression needs to be determined as CD80 expression is sensitive to post-transcriptional mechanisms that regulate its protein expression (61). This evidence concerns the gene CD80 and myeloid sarcoma.