CD4 and infection: Studies have shown that during normal ageing, T-cells become increasingly vulnerable to immunosenescence resulting in a poor frequency of functional naïve T-cell repertoire, increased rates of differentiation of naïve T-cells to terminally-differentiated T-cells, telomere shortening, decline in CD4/CD8 ratios and increased numbers of memory T-cells lacking CD28 co-stimulatory molecule, collectively culminating in increased rates of susceptibility to infections, autoimmune disorders, chronic inflammatory diseases and cancers [28,29,30].