| Summary: | These studies have shown that the fatty acid composition and membrane fluidity of head kidney macrophages from the rainbow trout, <I>Oncorhynchus mykiss</I>, are influenced by both diet and environmental factors. In particular, the fatty acid content and cholesterol concentration in various diets altered the membrane fluidity and phagocytic rate of head kidney leucocytes. The influence of temperature upon head kidney leucocyte composition and membrane properties depended on the rapidity of the temperature change encountered. Both abrupt and more gradual reductions of temperature produced an increase of the unsaturated/saturated fatty acid ratio of head kidney leucocytes, although these changes were more profound in the short term adaptive response to rapid reductions of temperature. These alterations to the fatty acid content also appeared to modify the membrane fluidity throughout the annual temperature cycle. The changes in both membrane fluidity and fatty acid composition of head kidney leucocytes in response to a 10°C decrease in temperature did not appear to be complete after 10 days. Adherent head kidney leucocytes isolated from winter fish also generated reduced quantities of leukotrienes following calcium ionophore challenge, compared with macrophages from summer acclimated fish. Monoclonal antibodies raised against macrophages did not exhibit the required specificity to enable the measurement of the mobility of a membrane-associated protein to be made by time-resolved phosphorescence anisotropy decay. The monoclonal antibody, 1.14, known to bind to trout lymphocyte surface Ig was, however, a suitable candidate for such measurements. Once purified, labelled and incubated with cells it was found that a large degree of movement was afforded to the phosphorescent probe-antibody complex. LTB<SUB>4</SUB> binding sites were identified on head kidney macrophages that appeared to bind to LTB<SUB>5</SUB> almost as efficiently as LTB<SUB>4</SUB>. Evidence suggests that LXA<SUB>4</SUB> recognition sites also exist and are separate to the LTB<SUB>4</SUB> binding sites.
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