Cell adhesion molecule 1 is upregulated in connective tissue mast cells and potentially contributes in IgE-mediated degranulation.

Mast cells are heterogeneous tissue-resident immune cells, with connective tissue mast cells (CTMCs) and mucosal mast cells in rodents exhibiting distinct phenotypes and activation profiles. Cell adhesion molecule 1 (CADM1), an immunoglobulin superfamily adhesion molecule, has been implicated in mast cell-nerve and mast cell-stromal interactions as well as in the pathogenesis of atopic dermatitis. Here, we investigated CADM1 function in CTMCs using a monoclonal antibody against the extracellular domain of CADM1, termed 3E1. CTMCs were differentiated from bone marrow-derived mast cells (BMMCs) by fibroblast coculture, where CADM1 expression was markedly upregulated compared with BMMCs. Treatment with 3E1 downregulated CADM1 expression and suppressed β-hexosaminidase release from IgE-sensitized, antigen-stimulated CTMCs by 18%, whereas BMMCs were unaffected. In addition, 3E1 reduced FM4-64-positive granule formation in activated CTMCs by 34.2% and 27.3% at 5 and 60 min, respectively. Confocal analysis further showed that 3E1 pretreatment decreased F-actin rearrangement in activated CTMCs by 66.2% at 5 min. In a passive cutaneous anaphylaxis model, intravenous 3E1 reduced dermal mast cell degranulation by 10.4%. These findings identify CADM1 as a regulator of IgE-mediated degranulation in CTMCs and demonstrate 3E1 as a valuable tool for dissecting mast cell heterogeneity in relation to tissue localization.