These subsets were chosen because they can represent more than 10% of circulating PBMCs in the groups under analysis and have been shown previously to express significant levels of IDO and ARG.14 No significant associations were observed with any cell population in the three blood donor groups suggesting the increase in IDO and ARG expression observed in CIS and MS was not linked to elevated numbers of a specific cell subset (data not shown). The gene discussed is IDO1; the disease is in situ carcinoma.