Differential macrophage polarisation during parasitic infections in common carp (Cyprinus carpio L.).

In many parasitic infections both classically activated macrophages (caMF) and alternatively activated macrophages (aaMF) play a pivotal role. To investigate if both types of macrophages also play an important role during parasitic infections in fish, we infected carp with either Trypanoplasma borreli or Trypanosoma carassii and determined the activation state of the head kidney leukocytes (HKL). Nitrite production was used as read-out for caMF and arginase activity as read-out for aaMF. Basal nitrite production and arginase activity of HKL were moderately different between the two infections. Differences were observed, however, after ex vivo re-stimulation of HKL. Re-stimulation with LPS and T. borreli lysates increased nitrite production by HKL of T. borreli-infected fish. Re-stimulation with cAMP increased arginase activity in HKL of T. carassii-infected fish. Our results indicate that T. borreli-infected carp are more prone to increase nitrite production by caMF while T. carassii-infected fish are more prone to increase arginase activity by aaMF.