The immune system of cyprinid fish. Oxytetracycline and the regulation of humoral immunity in carp (Cyprinus carpio).

The antibiotic oxytetracycline (oxyTC) was administered either by mixing with food or by intraperitoneal injections. On oxyTC treated animals decreased serum immunoglobulin levels were found. The primary anti-sheep red blood cells (SRBC) response was measured by enumerating plaque forming cells (PFC). It was observed that the PFC response was depressed by 80-95% in oxyTC treated animals. When an anti-SRBC serum was injected together with SRBC the immunosuppressive effect of oxyTC was absent. A secondary anti-SRBC response was not inhibited by oxyTC. On base of the results a model for antigen presentation and the interaction between macrophages, T- and B-like cells during primary and secondary responses in fish is proposed. In primary responses cellular interaction is needed to develop a proper immune response whereas after a high antigen dose challenge SRBC might behave as a T-independent antigen.