Post-infection, while both cell types significantly upregulated CD69 expression following TCR stimulation (Fig 2J and 2K), fold change was significantly higher for CD38- CD4+ T cells compared to CD38+ CD4+ T cells (average fold change of 13.7 and 1.4 for CD38- CD4+ T cells and CD38+ CD4+ T cells, respectively, p = 0.016). Here, CD4 is linked to infection.