Studies of Fc receptors of heart valve and joint fibroblasts.

Normal human and rabbit sera, and the IgG isolated from them, have been shown by immunofluorescence to react with bovine and human heart valve fibroblasts. Analogous results were obtained with sera of children under the age of 2. Positive reactions were observed also with fibroblasts, chondrocytes and osteocytes of human fetal joint tissues. The reactions are mostly due to monomeric immunoglobulins, since soluble immune complexes give much weaker reactions with the fibroblasts. The reactions are apparently dependent on the presence of Fc receptors on these cells. This conclusion is confirmed by positive reactions with IgG Fc fragments, with pure antibodies to ovalbumin and with human monoclonal IgG. The monoclonal IgG1 possesses the strongest ability to bind with fibroblast Fc receptors. No Fc-IgG receptors have been revealed on the fibroblasts and other structures of the interstitial connective tissue of human and bovine myocardium.