Local immune responses to two stages of Ichthyophthirius multifiliis in ginbuna crucian carp.

Ichthyophthirius multifiliis is a ciliated protozoan parasite and is known to infect many freshwater teleosts. Characterizing the immune system in epithelial tissues, where the parasites penetrate and settle, is key to understanding host-parasite interactions. This study examined local immune responses in vivo to the infective stage (theront and trophont) of the parasites using intra-fin administration, which has been developed to analyze in vivo immune responses using fish fin.

Innate cell-mediated cytotoxicity of CD8 T cells against the protozoan parasite Ichthyophthirius multifiliis in the ginbuna crucian carp, Carassius auratus langsdorfii.

Cytotoxic T cells are known to have the ability to kill microbe-infected host cells, which makes them essential in the adaptive immunity processes of various vertebrates. In this study, we demonstrated innate cell-mediated cytotoxicity of CD8 T cells against protozoan parasites found in the ginbuna crucian carp. When isolated effector cells such as CD8, CD4 (CD4-1), or CD8 CD4 (double-negative, DN), from naïve ginbuna crucian carp were co-incubated with target parasites (Ichthyophthirius multifiliis), CD8 cells from the kidney and gill showed the highest cytotoxic activity.