An FcμR expressed by channel catfish, Ictalurus punctatus, clonal CTL mediates inhibitory effector functions and recruits SHIP (43.7)

Abstract

Abstract Flow cytometric analyses of catfish clonal alloantigen dependent cytotoxic T lymphocyte (CTL) line, TS32.15, grown in the presence of 3% catfish serum revealed that all cells stain positive for IgM and both IgL F and IgL G isotypes, which suggests passive uptake of serum IgM via a putative FcμR. This IgM expression was sensitive to protease treatment, while phosphatidylinositol specific phospholipase C had no effect. Three FcμR or FcμR associated proteins of sizes 52, 40, and 38 kDa were co-immunoprecipitated from biotinylated TS32.15 CTL using anti-catfish IgM. Importantly, FcμR cross-linking led to tyrosine phosphorylation of the 52 kDa protein. Also, Western blot of immunoselect material demonstrated that Src homology 2 domain-containing inositol phosphatase (SHIP) was co-selected with the putative FcμR. However no increase in intracellular calcium was observed. Unlike the previously described catfish IgM bound by catfish NK cells, TS32.15 bound IgM did not mediate antibody dependent cell mediated cytotoxicity. In contrast, IgM cross-linking of TS32.15 cells resulted in reduced cell division and marked decrease in cytotoxicity against allogeneic targets. Cell cycle analyses revealed that cross-linked cells were predominately arrested in the G0/G1 phase and this blockage could be completely reversed by allogeneic stimulation. Together these data indicate this putative FcμR likely functions as an inhibitory Fc-receptor.