Canine mastocytoma CM-MC cells express two variants of high-affinity receptors for IgG

Abstract Rationale Most of mast cells express high-affinity receptors for IgE, but not for IgG. However, we found that canine mastocytoma CM-MC cells were activated by monomeric IgG, resulting in Ca 2+ response and mediator release. We therefore cloned cDNAs of high-affinity IgG receptor alpha chain (FcgRI) and determined the sequences. Methods The total RNA of CM-MC cells was prepared with TRIzol reagent and reverse-transcribed. The FcgRI cDNA fragments were amplified by PCR using primers which are highly-conserved sequences in humans and mice. The total cDNAs were prepared by 5'- and 3'-RACE and were sequenced. Results CM-MC cells express two variants of FcgRI mRNA. The longer variant is 1119bp and has 84% similarity to humans. The shorter variant lacks the first immunoglobulin domain (255bp). Conclusions Two variants of FcgRI mRNA were found to be expressed on the CM-MC cells. Although the biological function of the shorter variant is still unclear, CM-MC cells are useful for studying the mast cell activation via FcgRI.