Immunolocalization of p/ integrins in human gingival epithelium and cultured keratinocytes. Scand J Dent Res 1992; 100: 266-73. Beta 1 integrins are cell surface receptors for extracellular matrix binding. We have recently shown that these receptors may also play a role in cell-cell binding of human epidermal keratinocytes. In this study we used immunofluorescence and confocal laser scanning microscopy to localize beta 1 integrins in frozen sections of human gingiva and cultures of human gingival keratinocytes. The results show that beta 1 integrin polypeptides, localized by monoclonal and polyclonal antibodies, were detected mainly in the basal layer of the keratinized epithelium. There was also scattered staining in connective tissue fibroblasts, nerves, and blood vessel walls. In the basal layer, the integrins were found around the entire periphery of the basal keratinocytes. Furthermore, confocal laser scanning microscopy (CLSM) revealed that most of the staining was in fact localized in dot-like structures at the lateral cell membranes of neighboring basal cells. In cultured human gingival keratinocytes maintained in low calcium (0.15 mM) conditions pi integrins were localized in several different structures: trails which were left behind when the cells moved in culture, dots underneath the cells, around the nucleus, and in cell-cell contacts. The trails were also found to contain fibronectin and type IV collagen but not laminin. Switching the keratinocytes to high calcium (1.2 mM) conditions induced the formation of cell-cell contacts which were strongly positive for pi integrins. No fibronectin or type IV collagen was found in cell-cell contact sites. The results indicate that pi integrins are localized to cell-cell junctions of human gingival keratinocytes both in vivo and in vitro. Cultured cells also express these receptors in cell-matrix contacts indicating a dual role for pi integrins in cell-matrix and cell-cell contacts of human gingival keratinocytes.