CD4 and infection: Furthermore, considering that asymptomatic and symptomatic populations have similar CD4+Foxp3+ Treg frequencies prior to WNV infection, while asymptomatic patients exhibit greater Treg expansion within the first 2 weeks of infection [25], the proliferation and/or differentiation of CD4+Foxp3+ Tregs in asymptomatic persons seems to be promoted by unknown factors (molecular or cellular components) derived from WNV infection.