Methods: Human peripheral blood eosinophils were incubated with SEB (up to 18hr): sCD48 release (ELISA), CD11b expression (FC), phospholipases (PL) C/D activity (inhibitors), transport (brefeldinA), protein synthesis (RT-PCR, cycloheximide) were assessed (0-18 hrs). SEB peritonitis was induced in mice (100ug/mouse) and peritoneal cells (FC) and lavage examined.
Results: Eosinophils expressed mCD48 and intracellular CD48 that partly co-localized with ECP/EDN. SEB activated eosinophils released significant sCD48 that directly correlated to CD11b expression. Eosinophils activated by SEB in the presence of PL inhibitors or cycloheximide or brefeldin A, displayed decreased sCD48 indicating that PLs (C and D) are involved in the cleavage of mCD48 that is maintained by new synthesis and transport. sCD48 binds to SEB (ELISA) and eosinophils cultured with SEB pre-incubated with sCD48 released significantly less EPO and IL-8 and had a reduced chemotaxis. In SEB peritonitis, peritoneal sCD48 was elevated and correlated to eosinophils and lymphocytes. SEB pretreatment with sCD48 significantly downregulated peritonitis' various inflammatory parameters.
Conclusions: SEB regulates CD48 dynamics on eosinophils causing sCD48 formation that acts as a SEB decoy receptor. This highlights the importance of CD48 as a central player in eosinophil regulation in diseases such as allergy in which S. aureus is a primary pathogen.