DISTRIBUTION AND QUANTIFICATION OF ALPHA(1)-INTEGRIN SUBUNIT IN RAT ORGANS

The alpha(1) beta(1)-integrin is known to be a receptor for collagen a nd laminin mediating cell-matrix interactions. A monoclonal antibody, 33.4, which specifically inhibits the alpha(1)-integrin-mediated in vi tro cell-collagen binding of rat hepatocytes and hepatoma-derived A-ce lls (Loster et al., 1994), was used to purify by immunoaffinity chroma tography the alpha(1)-integrin subunit from rat liver in large quantit ies for inducing a polyclonal antiserum. In immunoblot analysis on mem brane extracts of several rat organs this polyclonal antiserum recogni zed only a 190 kDa-band, suggesting that it is highly specific for the alpha(1)-integrin subunit. A sandwich-ELISA with monoclonal antibody 33.4 and the polyclonal antiserum against the alpha(1)-integrin subuni t, respectively, enabled the quantitative expression pattern of the al pha(1)-integrin subunit to be studied in different rat organs. With th e exceptions of brain (not detectable) and muscle (low concentration), the alpha(1)-integrin subunit was detectable in almost all organs of the digestive, respiratory and urogenital system as well as in lymphat ic organs. The highest relative concentrations of alpha(1)-integrin su bunit were found in uterus, lung and spleen, whereas in seminal vesicl e, stomach, parotid gland, epididymis, kidney and liver only modest co ncentrations were evident. The organ distribution and localization of alpha(1)-integrin subunit were studied by immunohistochemistry with mo noclonal and polyclonal antibodies. Immunoreactivity was present in th e plasma membranes of all smooth muscle cells, vascular endothelial ce lls of many organs and fibrocyte-fibroblast sheaths in the heart and k idney. Since these cells are in close contact with collagen-containing basal membranes as well as reticular fibrils, strong evidence exists that in rat tissues the alpha(1)-integrin subunit is expressed at site s where collagen is present and might be involved in vivo in cell-coll agen binding.