Group IIA secretory phospholipase A2 (sPLA2- IIA) and group V secretoryphospholipase A2 (sPLA2-V) in the human mast cell line HMC-1

• Background: Mast cells (MC) are considered to be major effector cells in the pathophysiology of Crohn´s disease (CD). The variety of agents released from activated MC includes secretory phospholipase A2s (sPLA2s), small enzymes known to have both autocrine and paracrine actions of potential importance in inflammatory conditions. The expression of protease-activated receptor-2 (PAR-2) is increased on ileal mucosal MC in CD, however it is not known if this receptor influences the release of sPLA2s from MC. Despite extensive studies in rodent MC, not much is known about sPLA2s in human MC. The principle aims of this study were to investigate if the human mast cell line HMC-1 could serve as a model for studies on two sPLA2s implicated in inflammation, namely sPLA2-IIA and sPLA2-V, and if stimulation of PAR-2 influences the release of the two enzymes.Methods: HMC-1 cells were used for studies on sPLA2 expression by RT-PCR and immunocytochemistry. Degranulation and sPLA2 release was investigated by β-hexosaminidase assay and ELISA, respectively. sPLA2 expression in ileal CD specimens was investigated by immunohistochemistry. Results: In HMC-1 cells the basal expression of sPLA2-IIA seemed to be more pronounced than of sPLA2-V but only sPLA2-V was induced by TNF-α. A23187, but not the PAR-2 stimulator trypsin, caused release of the two enzymes. Both sPLA2-IIA and -V were detected in ileal MC of the CD specimens, but sPLA2-IIA seemed to be more abundant. Conclusions: HMC-1 cells express both sPLA2-IIA and sPLA2-V but the expression may bedifferently regulated by inflammatory cytokines. HMC-1 cells release sPLA2-IIA and sPLA2-V upon appropriate stimulation, although not by PAR-2 stimulation. These results make HMC-1 promising as a model for studies on these two enzymes in human MC. Indeed, the finding that both sPLA2-IIA and sPLA2-V are present in ileal MC in CD strengthens the relevance of such a model.

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