CD4 and infection: In our study, a reduction of splenic CD4+ Th cells and CD8+ Tc cells was identified, which may partially account for the inflammation and glucose intolerance in aged mice because CD8+ Tc cells are mainly responsible for fighting pathogen infections and inhibiting proinflammatory phenotypes via the secretion of perforin, and CD4+ Th cells have been reported to highly correlate with glucose tolerance and insulin sensitivity (Revelo et al., 2015; Winer et al., 2009).