A combined inhibitory effect of dexamethasone and CD300a on murine and human mast cell functions

Background: Mast cells (MC) can be down-regulated by activating targeted inhibitory receptors or using different drugs. It has been previously shown that the glucocorticosteroid (GC) dexamethasone exerts a dose-dependent inhibitory effect on murine-derived MC degranulation. In human cord blood derived MC (CBMC), dexamethasone decreases transcription and release of pro-inflammatory cytokines, while it has no effect on degranulation¹. In light of our recent work, we hypothesized that CBMC degranulation can be down-regulated by combining αCD300a-activating antibodies (Ab) with dexamethasone. The aim of the present study was to investigate the possible joint inhibitory effect of dexamethasone and αCD300a Ab on MC activation to achieve a GC sparing effect. 

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