Cross-linking of CD137 ligand modulates immune responses of thioglycollate-elicited mouse peritoneal macrophages

The aim of this study was to investigate effects of CD137 ligand (CD137L)-mediated reverse signaling on cellular responses in thioglycollate-elicited mouse peritoneal macrophages. Five-week-old male C57B6 mice were injected intraperitoneally with thioglycollate for 3 days to isolate peritoneal macrophages. We counted total cell numbers with a Cell Lab Quanta SC. CD137L expression was examined with a flow cytometer. We also measured expression of inflammatory cytokines by flow cytometry and/or real time-PCR. Cross-linking of CD137L with recombinant CD137-Fc protein (rCD137-Fc) increased total numbers of thioglycollate-elicited mouse peritoneal macrophages (hIgG-Fc- vs. rCD137-Fc-treated group, p < 0.05). However, ligation reduced the increase in IL-1 beta and IL-6 levels. Real-time PCR analysis showed that treatment of cells with rCD137-Fc also reduced transcript levels of IL-1 beta, IL-6, iNOS and COX2 (hIgG-Fc- vs. rCD137-Fc-treated group, p < 0.05), as well as expression of CD137L. Reverse signals initiated by CD137L negatively modulate certain immune functions of thioglycollate-elicited peritoneal macrophages.