Figure 7. Synergistic effects of IL-6 on antigen-induced in vivo IgM production.

Rainbow trout were injected i.p. with 100 μl of PBS, 100 μl of PBS with IL-6 (100 ng/fish), 100 μl of PBS with 2 × 10¹⁰ TCID₅₀/ml inactivated IPNV, or 100 μl of PBS containing the same amount of IPNV and IL-6. (a) The number of IgM secreting cells was evaluated at days 2, 6 and 15 post-injection in spleen and kidney leukocyte cultures by ELISPOT as described in the Materials and methods section (mean + standard deviation; n = 6). Asterisks indicate significant differences between groups as indicated. *P < 0.05. (b) Total IgM, IPNV-specific and natural (BSA; galactosidase; PC, phosphorylcholine; and poly I:C-specific) IgM titers were measured in the sera of fish killed at day 15 post-immunization by ELISA. Results are shown as absorbance at 405 nm (for total IgM) or absorbance at 492 nm (for specific IgMs) for individual fish. Bars indicate mean values in each group and asterisks denote significant differences between groups as indicated. *P < 0.05.