Randall Parker comments on recent discoveries relating to the way in which our immune system ages. "One subcategory of immune system cells may be aging more rapidly and causing most of the problem with reduced immunocompetence in the elderly. ... The authors show that old CD4 'helper' T cells cannot provide the stimulatory signals to B cells that prompt them to make antibodies. Old and young B cells, however, are equally effective if helped by young CD4 T cells." You might recall that researchers recently found that less useful CD8 T cells crowd out other types (such as CD4) as we get older. Understanding these processes is the first step on the path to fixing them - and thus rejuvenating age-affected immune systems.