Why is the antibody response of Atlantic cod so poor? The search for a genetic explanation

ABSTRACT:  The immune system of the Atlantic cod (Gadus morhua L) is unusual in that it cannot produce a specific antibody response upon immunization. Despite this, the cod is not particularly susceptible to infectious disease in its normal environment. This review examines the potential genetic basis for the lack of a specific antibody response in the cod. The genetics of cod immunoglobulins are compared with those of other well-characterized teleost fish. A review of the evidence suggests that deficiencies in the number, structure, organization, diversity and expression of both Immunoglobulin (Ig) heavy and Ig light chain genes in cod cannot explain its unusual antibody response. It is concluded that a deficiency in cod major histocompatibility (MH) class II molecules is a prime suspect for the lack of a specific antibody response in cod, and that testing of this hypothesis must await future experimentation.