ICOS and infection: In contrast, lymphopenia affected virtually all CD8+ central (CD8 TCM) and effector memory T cells (CD8 TEM) during active infection, and subsequent T cell subsets recovering to either baseline (ICOS+ TFH and HLADR+CD38- CD4+ T cells) or enriched (Treg TEM and HLADR+CD38+ CD8+ T cells) during late convalescence (Figure 3B).