Absence of 4-1BB increases cell influx into the peritoneal cavity in response to LPS stimulation by decreasing macrophage IL-10 levels.

Peritoneal injection of lipopolysaccharide (LPS) increased the influx of polymorphonuclear leukocytes and macrophages into the peritoneal cavity (PEC), with significantly higher cell numbers in the 4-1BB-deficient (KO) mice than in wild-type (WT) mice. The peritoneal macrophages of KO mice contained less IL-10 transcripts and protein than those of WT after LPS treatment, and immobilization of 4-1BB-Fc increased the level of IL-10. Injection of IL-10 resulted in lower cell numbers into the PEC of KO mice, suggesting that lower level of IL-10 is responsible for stimulated cell influx in KO mice due to lack of 4-1BB and 4-1BBL interaction.