Immunoglobulin heavy chains of three isotypes viz.,
IgM,
IgD and IgT/IgZ are described in teleosts. In this study, a challenge experiment with an ectoparasite Argulus siamensis was conducted to evaluate the changes in adaptive immune response by quantitation of expression of
Ig heavy chains in skin, head kidney and mucus of infected rohu, Labeo rohita. Rohu were challenged with 100 metanauplii of A. siamensis/fish. Head kidney, skin and mucus samples were collected at 0 h, 12 h, 24 h, 3 d, 7 d, 15 d and 30 d by sacrificing four fish each from infected and control groups at each time point. The expression of
IgM,
IgD and IgZ in these tissues were measured by reverse transcription real time quantitative PCR.
IgM level was found to reach its peak significantly 30 d post-
infection in head kidney tissue, while
IgM transcripts were below detectable range in skin and mucus at all time points. IgZ and
IgD levels were significantly up-regulated post-
infection in all the three tissue samples. Early up-regulation of
IgD was observed in skin and mucus, compared to head kidney. This study showed that parasitic invasion can trigger varied expressions of
immunoglobulin types to provide systemic as well as local protection in the host. In particular, the appearance of high level of expression of IgZ and
IgD in skin and mucus will pave the way for
vaccine development against A. siamensis which feeds on those tissues.