Immune responses in an air-breathing teleost Clarius batrachus

Abstract

The kinetics of the primary and secondary response to a particulate antigen, sheep red blood cells (SRBC), was investigated in terms of antibody-secreting cells by a plaque forming cell (PFC) assay and haemagglutination (HA) tests. Plaque forming cells were found in all the lymphoid organs including the thymus. The antibody response was observed on the second day of immunisation, with a peak PFC response at 5 days after both primary and secondary challenge. Circulating antibodies were detected on the second day by the HA technique with a peak on the 10th day, whereas the peak of the HA titre during the secondary response was attained on the 7th day. The agglutinating antibodies produced after both the first and second injections were 2-mercaptoethanol sensitive, indicating that they are equivalent to the IgM of mammalian species. The cell-mediated immune response in terms of delayed type hypersensitivity reaction was observed with 2,4,-dinitrofluorobenzene (DNFB), a soluble sensitising agent. Maximum induration was observed 72 h after the secondary challenge. In addition, non-specific lytic factors which are characteristic of invertebrates were found in the serum of Clarius batrachusagainst different types of erythrocytes.