The primary immune response of brown trout (Salmo trutta) to cellular and soluble antigens: Enumeration of antibody-secreting and antigen-binding cells, and the production of antibody.

Significantly increased numbers (P less than 0.01) of antigen-binding (ABC) and antibody-secreting cells (ASC) were stimulated, in the spleen and the anterior kidney (AK) of the brown trout (Salmo trutta), by a single intraperitoneal injection of Salmonella typhimurium lipopolysaccharide (LPS), keyhole limpet haemocyanin (KLH), sheep red blood cells (SRBC) or KLH- or LPS-coated SRBC. With the exception of the SRBC group, the spleens contained more AVC and ASC per 10(6) lymphoid cells than the AK. Fewer ASC were found when guinea pig complement was used than with salmon serum; with 3 exceptions the differences were significant. In both organs, ABC and ASC were detected between 2 and 4 days after injection and maxima were reached between day 14 and day 18 in most of the experimental groups. However, with fish immunised with SRBC, ABC and ASC first occurred on day 6 and peak counts were obtained on day 12. In all groups the counts had returned to background levels by day 28. The coupling of LPS or KLH tro SRBC, with one exception, significantly increased the numbers of ABC and ASC (p less than 0.02) compared to when uncoated SRBC, LPS or KLH were injected. There was no significant change when the ABC results for antigen-coated SRBC were compared to those obtained when LPS was injected by itself. Following antigenic stimulation there were significant increases (p less than 0.05) in most cases in both the spleen and the AK to body weight ratios. There were significant differences in both the spleen and the AK to bodyweight ratios. There were significant differences (p less than 0.001) between KLH and KLH-SRBC (spleen and AK), LPS and LPS-SRBC (spleen and AK) and SRBC and LPS-SRBC (AK alone). Antibodies were detected 2 to 8 days after sensitised cells were first found and reached maxima 5 to 16 days after the cellular responses. The titres obtained with experimental sera were significantly different (p less than 0.001) compared to the appropriate control groups.