Methods: CBMC or bone marrow-derived MC (BMMC) were sensitized with IgE and treated O.N with either dexamethasone or vehicle. αCD300a Abs (30 min) or IgG1 isotype control were added followed by an FcεRI cross-linking activating Ab for 30 min for degranulation, or 18 hrs for cytokine release. Degranulation was measured using beta-hexosaminidase release (enzymatic assay) and cytokine release (ELISA). Membranal expression of CD300a was evaluated on CBMC/BMMC and mRNA was assessed in BMMC following 18 hrs by flow cytometry and RT-PCR, respectively.
Results: Incubation of both CBMC/BMMC with dexamethasone did not lead to a significant change in the expression of membranal CD300a. However, dexamethasone dose-dependently decreased CD300a mRNA levels in BMMC (18hrs). Incubation of CBMC with suboptimal concentrations of dexamethasone and αCD300a increased IL-10 secretion and decreased GM-CSF release and cell degranulation. Moreover, in BMMC, αCD300a Abs (10ug/ml) with dexamethasone (10-8 M) elicited a strong inhibition of MC degranulation, as potent as a higher dose (10-7 M) of dexamethasone alone.
Conclusions: Our results show that αCD300a combined with dexamethasone (at low concentrations) decreased CBMC degranulation and the release of the pro-inflammatory cytokine GM-CSF, while it enhanced the release of the anti-inflammatory cytokine IL-10. This indicates that CD300a activation might serve as a tool to improve dexamethasone treatment by an additional inhibition mechanism leading to a GC-sparing effect.
References: 1. Smith SJ. et al. “Dexamethasone inhibits maturation, cytokine production and FCεRI expression on human cord blood-derived mast cells” , Clin Exp Allergy, 2002,32(6):906-13