Comparative Assessment of Edwardsiella ictaluri Live Attenuated Vaccine and Wild type Strains-induced Phagocytic Vesicle Formation and Apoptosis in Catfish B cells - Abstract
In this study, we applied comparative morphological assessment of autophagic changes in catfish anterior kidney (AK) B cells after exposure to Edwardsiella ictaluri live attenuated vaccines (LAVs; Ei?evpB and ESC-NDKL1) and wild-type (WT) strains. Bacterial uptake followed by induced phagocytic vesicle formation and late apoptotic changes were analyzed by applying light compound microscopy and blind cell counting to the slides with fixed Giemsa stained highly enriched IgM+ AK B cells. We confirmed and extended our previous report on the ability of catfish AK B cells to engulf and eliminate E. ictaluri WT and LAV strains. Importantly, in this study we documented significant decreases in the percentage of B cells with internalized bacterial strains combined with significant increases of cells with phagolysosome vesicles alone after exposure to the Ei?evpB strain compared to the repressed vesicle formation by the ESC-NDKL1 and WT strains. This observation suggested the higher intensity of catfish B cells in killing the Ei?evpB LAV strain compared to the ESC-NDKL1 and WT strains after initial short-term bacterial exposure. Furthermore, we showed that the WT strain had a more profound proapoptotic effect on catfish B cells compared to the Ei?evpB and ESC-NDKL1 counterparts. Despite the initial advantage in vesicle formation activity against Ei?evpB strain, the subsequent increase in the killing ability of ESC-NDKL1 previously reported in catfish B cells suggests an advantage of the strain to be specifically recognized as inducing protective immunity against enteric septicemia of catfish (ESC). Moreover, losing the pathogenicity of ESC-NDKL1 by significantly repressing apoptosis could be used as a tool in vaccine design. Our data suggest that catfish B cells possess important phagocytic and microbicidal ability in initiation of protective innate and adaptive immune responses against ESC.