Kinetics of Parasite-Specific Antibody and B-Cell-Associated Gene Expression in Brown Trout, Salmo trutta during Proliferative Kidney Disease

SIMPLE SUMMARY: The parasite Tetracapsuloides bryosalmonae causes proliferative kidney disease in salmonids. In general, antibodies and B cells play important roles in host defense during chronic infections. In this work, we studied the antibody and B-cell-associated gene expression of brown trout during the course of T. bryosalmonae infection. Our results show that antibody responses mounted by brown trout change over time and are maintained at a low level throughout the infection duration. This might be reflective of the host strategy to limit parasite numbers for its survival. Additionally, the expression of genes having important roles in the development, differentiation and signaling of B cells was analysed in the kidney and spleen of infected brown trout from preclinical to post-clinical phases. Our findings indicate that the expression of B-cell-associated genes modulate during the course of parasite development which is suggestive of their critical role for protecting the host against this parasitic invasion. This study brings in important knowledge about the antiparasite antibody and B-cell-associated gene response in infected brown trout, which could be instrumental in developing therapeutic and prophylactic measures against this parasite in future. ABSTRACT: Tetracapsuloides bryosalmonae, a myxozoan endoparasite often causes chronic infection in brown trout. Antiparasite immunity mediated by antibodies and B cells is known as an important determinant of host survival and parasite proliferation during chronic infections. Accordingly, studying their time course during proliferative kidney disease (PKD) might be helpful in improving our understanding of its chronic nature. Therefore, we conducted this study to examine parasite specific serum antibody and B-cell-mediated response in laboratory-infected brown trout at different time points. Brown trout were exposed to the spores of T. bryosalmonae, derived from infected bryozoans. Samples were collected at different time points and processed for indirect ELISA, histopathology, and qRT-PCR. T. bryosalmonae specific antibody was detected at 4 weeks post exposure (wpe) and it persisted until 17 wpe. Additionally, the expressions of C4A, CD34, CD79A, BLNK, CD74, BCL7, and CD22 were differentially regulated in the important immune organs, kidney and spleen. To our knowledge, this is the first study addressing anti-T. bryosalmonae antibody response in brown trout at different time points. The results from this study provide valuable insights into the processes leading to changes in B cell development, inflammation and antibody production during the course of PKD in brown trout.