The immunologists' debt to the chicken

1. The immune system of the chicken is an invaluable model for studying basic immunology and has made seminal contributions to fundamental immunological principles. Graft versus host responses and the key role of lymphocytes in adaptive immunity were first described in work with chicken embryos and chickens. 2. Most notably, the bursa of Fabricius provided the first substantive evidence that there are two major lineages of lymphocytes. Bursal-derived lymphocytes, or B cells, make antibodies while thymus-derived, or T cells, are involved in cell-mediated immune responses. 3. Gene conversion, the mechanism used by the chicken to produce its antibody repertoire, was first described in the chicken and requires the unique environment of the bursa. Subsequently it has been shown that some mammals also use gene conversion. 4. The chicken's Major Histocompatibility Complex (MHC), the first non-mammalian MHC to be sequenced, is minimal, compact and some 20-fold smaller than that of mammals. Uniquely, the chicken M...