Induction of both local and systemic immunity by in vivo injection of PHA into ginbuna carp fin.

Phytohemagglutinin (PHA) is a well-known mitogen inducing activation and proliferation of lymphocytes, particularly T lymphocytes in vitro. PHA has also been used in vivo for assessing cell-mediated immunity in non-mammalian vertebrates, particularly in birds. However, it has been suggested that local inflammation as a direct result of tissue damage could be responsible for skin swelling after PHA injection, in addition to induction of T lymphocyte mitogenesis. In order to understand the complex nature of this response in fish we investigated the accumulation of cell types chronologically in dorsal fin of ginbuna crucian carp Carassius auratus langsdorfii after PHA injection. Neutrophils appeared first and showed a peak response on day 1, decreasing gradually and followed by macrophages and blast cells while lymphocytes increased later with a peak response on day 5. The number of accumulated cells was significantly higher in PHA-injected fish than controls in most cases. Lymphocytes identified as CD4-1and CD8α were significantly more abundant in PHA-injected fish than in control fish throughout the 7-day experimental period except on day 1, while the number of IgM lymphocytes was higher in PHA-injected fish only on day 1. In the blast cell fraction, the number of CD4-1 lymphocytes was significantly higher in PHA-injected fish than in control fish throughout experimental period, except on day 1. We also document the migration of neutrophils from the kidney to the fin through blood, followed by granulopoiesis in the kidney. These results suggest that adaptive immunity as well as innate immunity was induced by in vivo stimulation with PHA.