CD40 and HIV-1 infection: Given that thymocytes of different maturation are found in the cortex and medulla, and our findings demonstrated that thymic pDC were able to transfer productive R5 HIV-1 infection to thymocytes, we next examined the distribution of pDC within the human thymus using antibodies to CD123, HLA-DR, CD68, CD83 and CD40 (Figure 5A).