Characterization of Fcγ receptors on rat mucosal mast cells using a mutant FcϵRI‐deficient rat basophilic leukemia line

摘要

AbstractA novel rat basophilic leukemia (RBL) 2H3 subline of rat mucosal mast cells deficient in the expression of the γ chain (RBL‐γ‐) has permitted functional characterization of their low‐affinity Fcγ receptors (FcγR). A rat FcγRII analog of the mouse b2 isoform has been earlier identified and its transcript detected in RBL‐2H3 cells. We have noew isolated and sequenced the rat FcγRIIb1 isoform and observed differences between its expression in RBL‐2H3 and RBL‐γ‐. Furthermore, we demonstrate that rat mucosal mast cells express a second, low‐affinity Fcγ receptor, namely the FcγRIII. Stimulation of either cell line with IgG complexes decreased the expression of transcripts for all FcγR. Hence, ligation of FcγR on rat mucosal mast cells apparently regulate their transcription. Selective stimulation through the FcγRII or FcγRII/III systems, respectively, was accomplished by either using RBL‐γ‐ line or by saturating the FcγRI on RBL‐2H3 with monomeric IgE. RBL‐γ‐ cells, which do carry FcγRII (but lack FcγRI and FcγRIII), do not respond to IgG (and IgE) immune complexes as monitored by specific protein tyrosine phosphorylation, degranulation or cytokine secretion. This finding, together with the restoration of the functional phenotype of parental cells upon γ chain cDNA transfection into RBL‐γ‐ cells, unequivocally excludes the possible stimulation of rat mucosal mast cells by clustering of their FcγRII. FcϵRI saturation by IgE on parental RBL‐2H3 cells completely blocks their response to IgG immune complexes. Thus the FcγR on these cells do not trigger degranulation and this is not due to the absence of FcγRIII as previously suggested. Therefore, co‐clustering of FcγRII and FcγRIII on rat mucosal mast cells does not seem to stimulate them. A possible inhibito