Proliferative responses of rainbow trout, Oncorhynchusmykiss, T and B cells to antigens of Aeromonas salmonicida

A mouse monoclonal anti-trout Ig (I-14) was used in a panning technique toseparate rainbow trout, Oncorhynchus mykiss, peripheral blood leucocytes (PBL) into sIg^- (T) and sIg⁺ (B) cell populations. The ability of these separated populations and unfractionated PBL to proliferate to various whole cell antigen preparations of A. salmonicida was investigated, using cells from fish injected previously with an A-layer negative strain (MT004) grown under iron-restricted conditions or saline (controls). All primed cell populations demonstrated enhanced responses to A. salmonicida antigens above their respective controls, indicative of both T and B memory cell formation in vaccinated individuals. Interestingly, both T and B cell populations from primed fish were also able to respond to an A-layer positive strain (MT423) of A. salmonicida, suggesting that both forms of bacteria share common immunogenic T and B cell epitopes. However, responses to the A-layer positive strain by cells from both primed and control fish were found to be of a lower magnitude than those to the same dose of the A-layer negative strain, particularly at the lower doses used to stimulate proliferation in vitro. Proliferative responses of these PBL populations to whole A. salmonicida preparations, grown with or without iron restriction, were also generally slightly higher using iron-restricted bacteria but not significantly so.