CTLA4 and infection: Consistent with this notion, we observed that although subjects with neuroinvasive and asymptomatic WNV infections had similar proportions of CD4+CD25+ CD127lowFoxp3++ cells (implying similar numbers of Treg), Tregs from subjects with neuroinvasive infection had a significantly lower proportion of CTLA-4 expression, which has been shown to be intimately linked to effective suppressive function [20].