Effect of Dactylogyrus catlaius (Jain 1961) infection in Labeo rohita (Hamilton 1822): Innate immune responses and expression profile of some immune related genes

The monogenean ectoparasite, Dactylogyrus sp. is a major pathogen in freshwater aquaculture. The immune responses in parasitized fish were analyzed by quantitation of innate immune factors (natural agglutinin level, haemolysin titre, antiprotease, lysozyme and myeloperoxidase activities) in serum and immune-relevant gene expression in gill and anterior kidney. The antiprotease activity and natural agglutinin level were found to be significantly higher and lysozyme activity was significantly lower in parasitized fish. Most of the genes viz., beta 2-microglobulin (beta 2M), major histocompatibility complex I (MHCI), MHCII, tumor necrosis factor alpha (TNF alpha) and toll-like receptor 22 (TLR22) in gill samples were significantly down-regulated in the experimental group. In the anterior kidney, the expression of superoxide dismutase and interleukin 1 beta (IL1 beta) were significantly up-regulated whereas a significant down regulation of MHCII and TNF alpha was also observed. The down-regulation of most of the genes viz, MHCI, beta 2M, MHCII, TLR22 and TNF alpha in infected gills indicated a well evolved mechanism in this parasite to escape the host immune response. The modulation of innate and adaptive immunity by this parasite can be further explored to understand host susceptibility.