Gene and protein expression of a soluble form of CTLA-4 in a healthy dog.

Cytotoxic T lymphocyte associated gene-4 (CTLA-4) is a costimulatory molecule, expressed on the surface of activated T cells that negatively regulates T cell activation. In humans, alternative splicing of the CTLA-4 gene generates two major isoforms of mRNA, and a soluble form of CTLA-4 (sCTLA-4) was detected in normal human serum. We describe alternatively spliced mRNA expressed in peripheral blood mononuclear cells obtained from a healthy dog lacking the transmembrane domain coded by exon 3 of the CTLA-4 gene. Immunoprecipitation and western blotting of dog serum revealed a band of approximately 23-kDa, which is consistent with the predicted size, based on the amino acid sequence of the canine sCTLA-4 obtained in this study.