When aged mice were supplemented with young CD4+ T cells prior to infection (aged + CD4 group), the number of total (Fig. 1K) and NP specific (Fig. 1L) GC B cells reaches that of the endogenous response of young mice (young group) at 14 dpi, emphasizing the importance of efficient CD4+ T cell help in the development of a robust B cell response. The gene discussed is CD4; the disease is infection.