Cell-mediated immune response of goldfish, Carassius auratus (L.), to Ichthyophthirius multifiliis

Abstract

Goldfish, Carassius auratus (L.), were intraperitoneally injected with two doses of Ichthyophthirius multifiliis (each containing 2.3 × 106 live tomites) in saline, 30 days apart. The control fish were injected with saline only. Two weeks after the last vaccination, fish of both groups were intradermally injected with 2.5 × 105 live tomites for skin tests. The skin at the antigen-injected site of the vaccinated fish increased in thickness from 8 h onwards and reached a peak at 24 h. Histological study showed a heavy infiltration of mononuclear leucocytes at the antigen-injected site. In contrast, no such changes were encountered in control fish. The migration area of pronephros cells from the vaccinated fish was significantly inhibited, in vitro, compared to controls with the presence of antigens. These findings suggest that the tomite-vaccinated fish produced a cell-mediated immune response. However, vaccinated fish also exhibited significantly higher titres of immobilizing antibodies in their sera and mucus than the controls. Therefore, it is likely that both humoral and cell-mediated immune responses have to work closely together to eliminate the infectious tomites of I. multifiliis which succeed in penetrating the fish epithelial tissues.