Modulation of MHC class II expression in rainbow trout Oncorhynchus mykiss macrophages by TNFα and LPS

Modulation of MHC class II β chain expression on head kidney macrophages has been demonstrated. Following in vitro stimulation for 24 h, 48 h or 72 h with human recombinant TNFα plus LPS increased numbers of MHC class II positive macrophages were found relative to control cells, by FACS analysis with an anti-trout MHC class II β chain serum. Northern blot analysis confirmed that increased transcription was occurring. That TNFα synergised with LPS was also clearly demonstrated using Northern blots, where TNFα induced no effect whilst LPS alone had a small stimulatory effect. A time course experiment demonstrated that 4 h post-stimulation was an optimal time to isolate macrophage RNA post stimulation with TNFα and LPS, with later times showing less clear modulation of MHC class II β expression. Lastly, a dose response experiment performed with LPS alone revealed that only small (if any) effects were apparent when using 6·25 and 12·5 μg ml^-1, whereas 25 and 50 μg ml^-1 were equally stimulatory. The mechanisms and consequences of modulating MHC class II expression are discussed.