CD4 and HIV infectious disease: Based on our previous findings that mitochondrial mass (MM) in CD4+T cells gradually increases in association with the progressive loss of CD4+T cells during HIV infection [12], and that pyroptosis accounts for 90% of CD4+T cell death [6], we hypothesized that the increased MM in CD4+T cells may be related to their susceptibility to pyroptosis, and tested the hypothesis by using MitoLite TM Orange FM as an index of MM [33] and caspase-1 staining for pyroptosis [6].