Bacteriolytic activity of rainbow trout ( Oncorhynchus mykiss) complement

The total bacteriolytic activity comprising of the classical, alternative and possible lectine pathways as well as the bacteriolytic activity of the alternative pathway (AP) of rainbow trout ( Oncorhynchus mykiss) complement was assessed in temperatures ranging from 0 to 35 °C against a recombinant strain Escherichia coli containing two reporter genes gfp and lucFF. At 35 °C there was no difference between the total (TC) activity and the activity of the AP, but at 10 °C the TC was notably higher than the AP. Total activity peaked at 30 °C and gradually grew smaller towards 0 °C. The activity of the AP was similarly temperature-dependent, but CB50 value was found to be beyond measurable range at temperatures below 10 °C. When compared to human serum complement, the peak human TC activity at 37 °C was four times higher than the TC of rainbow trout at 30 °C. Human TC activity was 10.1-fold lower at 25 °C when compared to the activity at 37 °C. At 37 °C the human AP bacteriolytic activity was 4.5-fold less effective than human TC, but at 25 °C there was no difference between human TC and AP. In contrast to previous reports where AP activity of fish was assayed as hemolytic activity our study showed that the bacteriolytic activity of AP was lower than that of TC and very low at temperatures below 10 °C suggesting that the earlier proposed particular importance of AP in fish should be reconsidered.