The Thai Journal of Veterinary Medicine


An immunohistochemical study describes the localization of IgM containing cells involved in the primary immune organs of tilapia and the fate of E. tarda antigen distributed in the tissues during a course of intraperitoneal challenge. The E. tarda antigen was diffusely detected in various organs except the brain and spinal cord. The positive signals were identified within various cell types, including phagocytic cells, serosal mesothelia, myocardia, intestinal and gill epithelia and glomerular capillary endothelia. No extracellular deposition of bacterial antigen was observed. The bacterial antigen can persist up to 1 month in the granuloma and melano-macrophage center, confirming the intracellular invasive ability of E. tarda disseminated in the tissues during septicemia. The granuloma-participating phagocytic and IgM containing cells play an important role in the specific immune response against E. tarda during septicemia. The IgM containing cells uniformly distributed as a peri-granuloma arrangement at 7-14 DPI. E. tarda antigen decreased significantly after the appearance of IgM response, suggesting the phagocytic enhancement of granuloma-participating cells to eliminate E. tarda bacteria was influenced by these IgM cells.

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