Differential effects of temperature and exogenous fatty acids on mitogen-induced proliferation in channel catfish T and B lymphocytes

1. Exogenously supplied, BSA complexed saturated and unsaturated fatty acids were compared for their effects on mitogen-induced DNA synthesis in channel catfish T and B lymphocytes. 2. At "permissive" in vitro temperatures (27 degrees C), high concentrations (greater than or equal to 240 microM) of all the fatty acids used were inhibitory. However, at lower concentrations (80-160 microM), differences were noted in the ability of some fatty acids to modulate mitogen responses. While palmitic acid (16:0) and linoleic acid (18:2) had little effect on LPS-induced B cell- or Con A-induced T cell proliferation, stearic acid (18:0) suppressed while oleic acid (18:1) enhanced T cell responses only. 3. Adding equimolar amounts of 18:0 and 18:1 obviated the effects of singularly added fatty acids on T cell mitogenesis. 4. 18:1 was used to successfully "rescue" approximately 60% of the Con A-induced T cell proliferation normally inhibited at "nonpermissive" in vitro temperatures (17 degrees C). 5. While B cells readily appear to desaturate 18:0 and synthesize unsaturated fatty acids, T cells accumulate comparatively large amounts of 18:0 in membrane associated phospholipids. 6. It is proposed that 18:1 enhances T cell responses at permissive high temperatures and rescues suppressed T cell responses at nonpermissive low temperatures by increasing membrane fluidity.