Murine thymic nurse cells express ICAM-1 on caveolar and vacuolar membranes

The thymic nurse cell is a unique type of epithelial cell in the thymic cortex. It is in intimate contact with the developing thymocytes by harbouring up to 200 thymocytes in distinct vacuoles, called caveoles. This investigation is concerned with the nurse cell expression of the intercellular adhesion molecule ICAM-1, the ligand for thymocyte LFA-1. Nurse cells from young Balb/c mice were isolated in a density gradient. ICAM-1 expression was studied by using two different immunotechniques: alkaline phosphatase labelled cryosections, and immunogold electron microscopy. The specific antibody was a monoclonal rat anti-mouse ICAM-1. Immunostaining of cryosections demonstrated that ICAM-1 is expressed on the surface membrane and in the internal caveolar membranes of thymic nurse cells. Electron microscopy of immunogold labelled sections revealed ICAM-1 on the surface membrane of thymic nurse cells and on the membranes of the caveoles, the small cytoplasmic vesicles, as well as on the Golgi apparatus.