“…Notably, germinal centre and plasma cell development could be restored in irradiated and bursectomized birds by reinfusion of their bursal cells 33 . Irradiated, bursectomized and thymectomized birds resembled infection-prone infants who had congenital agammaglobulinaemia, no lymphocytes and deficient cell-mediated and humoral immune responses 34,35 . These composite findings 50 years ago offered a clear view of separate thymus-dependent and bursa-dependent lineages of lymphocytes that mediate cellular and humoral immunity, respectively (FIG.…”