Fibronectin is a major surface-associated glycoprotein of cultured fibroblasts and it is also present in human plasma. Antiserum specific for human fibronectin was used to study the distribution of fibronectin in normal adult human tissues. The protein was detected (a) characteristically in various basement membranes including capillary walls: (b) around individual smooth muscle cells and in the sarcolemma of striated muscle fibers; and (c) in the stroma of lymphatic tissue and as thin fibers in loose connective tissue. The distribution of fibronectin was distinct from that of collagen and elastic fibers, but was very similar to reticulin, as demonstrated by conventional histological staining. The results indicate that fibronectin is a major component of connective tissue matrix. The distribution also indicates that most types of adherent cells abut fibronectin-containing structures. This supports the possible role of fibronectin in cell-cell and cell-matrix interactions in tissues.

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