Characterization of an early signaling defect following FcɛRI activation in the canine mastocytoma cell line, C2

A comparison of IgE recognition by cognate receptors expressed on the C2 canine mastocytoma cell line with analogous events in a rat basophilic leukemia cell line transfected with the α-chain subunit of the canine high-affinity IgE receptor using flow cytometry show that canine IgE recognizes the α-chain of its cognate receptor on both cell lines. Our study confirms the expression of functional IgE receptors in both cell lines, but receptor-mediated signaling in the C2 line only supports the early stages of downstream signaling as shown by the phosphorylation of the γ-chain and the failure to effect the phosphorylation of Syk. In contrast RBL-2H3 cells respond to sensitization with IgE and challenge with cognate antigen with tyrosine phosphorylation of the γ-subunits of the receptor complex followed by downstream phosphorylation of Syk and Ca2+ mobilization, culminating in β-hexosaminidase release. We propose that the identification of the precise signaling defect in C2 cells will yield useful information regarding the pathway leading to mast cell exocytosis and facilitate the restoration of the complete signaling cascade through complementation of the missing/defective signal transducer since signaling events downstream of Ca2+ mobilization are intact as demonstrated by β-hexosaminidase release following non-immunologic stimulation with the calcium ionophore, A23187.