CD38 and infection: In LCMV clone 13 infection, one TRM cell cluster expressing PD-1, CD38, CD39, CD54, and CXCR6 significantly associated with the liver, whereas a TEM cell subset of cells expressing high levels of PD-1, CX3CR1, NKG2A, and Ly6C (Cl13 cluster 5) was more abundant in the lungs and spleen (Figure 3E).