Molecular cloning of a soluble form of the granulocyte‐‐macrophage colony‐stimulating factor receptor α chain from a myelomonocytic cell line. expression, biologic activity, and preliminary analysis of transcript distribution

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Abstract
Objective. To analyze the molecular and functional characteristics of a soluble form of the granulocytemacrophage colony‐stimulating factor receptor α chain (sGM‐CSFRα), and analyze transcript expression in immune cells and the cellular constituents of rheumatoid arthritis synovial tissue. Methods. We amplified, cloned, and expressed the sGM‐CSFRα and transmembrane form of the receptor (tmGM‐CSFRα) from complementary DNA derived from a human myelomonocytic cell line. Competitive polymerase chain reaction assays were developed to determine the absolute and relative amounts of tmGM‐CSFRα versus sGM‐CSFRα message synthesized by various cell lines and tissues.S Results. sGM‐CSFRα transcripts were detected in bone marrow, monocyte/macrophages (cultured in GM‐CSF), rheumatoid synovial tissue, and rheumatoid synovial tissue T cell lines, and represented the predominant transcript in synovial fibroblasts and osteoarthritis synovial tissue. Levels of expression in monocyte/macrophages and some synovial fibroblast and T cell lines approached those seen in transfected cell lines producing functional sGM‐CSFRα. Conclusion. sGM‐CSFRα represents a functional antagonist of GM‐CSF activity in vitro. Expression of sGM‐CSFRα in bone marrow, rheumatoid synovial tissue T cells, and synovial fibroblasts suggests an important role in vivo, both in regulating myelopoiesis and in modulating the immune response.

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