Antigen uptake and immunoglobulin production in Atlantic cod (Gadus morhua L.) after intraperitoneal injection of Vibrio anguillarum

Atlantic cod (Gadus morhua L.) were injected intraperitoneally with formalin-killed Vibrio anguillarum bacteria. Immunostaining revealed uptake of V. anguillarum antigens especially in the spleen after intraperitoneal (i.p.) administration. The uptake was time dependent in the interval 1–24 h. Most of the antigen uptake in the spleen was concentrated in areas around small blood vessels, while immunoglobulin producing cells were localised to some thick walled arteries. There was apparently little or no co-localisation of antigens and antibody producing cells. In the heart, some of the high endocardial endothelial cells of the atrium contained bacterial antigens and in head kidney some macrophage-like cells were stained. Very little antigen was found in the pigmented loose connective tissues of the peritoneum. In contrast, endothelial cells of the underlying blood vessels contained substantial amounts. In the heart, peritoneum and anterior kidney the number of antigen positive cells did not seem to change in the time interval 1–24 h. After i.p. immunisation with a mixture of V. anguillarum and Freunds complete adjuvant, the humoral immune response in Atlantic cod was low when tested 21, 42 and 105 days later. There was apparently no enhanced number of immunoglobulin synthesising cells caused by the antigen stimulation.