In vitro effects of staphylococcal leukocidin LukE/LukD on the proliferative ability of lymphocytes isolated from common carp (Cyprinus carpio L.)

Various strains of Staphylococcus aureus bacteria produce bicomponent toxins such as leukocidin LukE/LukD consisting of two subunits S (LukE) and F (LukD). The toxin subunits bind to leukocyte cell membrane inducing transmembrane pore formation and subsequent cell lysis. There is a lack of data on the effects of staphylococcal leukocidin LukE/LukD on fish immunocompetent cells in vitro. The purpose of the study was to determine the influence of leukocidin LukE/LukD on the proliferative ability of T and B lymphocytes isolated from head kidney and spleen of common carp (Cyprinus carpio L.). The response of T and B lymphocytes was stimulated with concanavalin A (ConA) and lypopolysaccharide (LPS) respectively and measured by the MTT test. The results revealed the modulatory influence of staphylococcal leukocidin LukE/LukD on the proliferative ability of fish T and B lymphocytes. The highest concentrations (5000–25000 ng ml−1 of medium) of complete leukocidin LukE/LukD and its subunit LukE induced statistically significant suppression of both head kidney and splenic T and B lymphocyte proliferation. On the other hand, the lowest concentrations of the complete toxin (0.32-1.6 ng ml−1 of medium) caused slight but statistically significant stimulation of both head kidney and splenic T and B lymphocyte proliferative ability. No modulatory effects were observed at any concentration of subunit LukD used in the experiment. There is a need for further studies concerning the susceptibility of other immune cell populations isolated from fish to different types of staphylococcal leukocidin.