Vascular endothelial cells present alloantigens to unprimed lymphocytes.

Antigen-presenting cells (APC) were removed from canine peripheral blood by carbonyl iron treatment and adherence to plastic and to nylon-wool. This treatment resulted in low proliferation in mixed lymphocyte cultures (MLC) and lack of generation of cell-mediated cytotoxicity (CMC) in depleted cell suspensions compared with untreated cell suspension. The proliferative response could be restored to normal by the addition of low numbers of autologous arterial or venous endothelial cells to the MLC of depleted cell suspensions. Cytotoxicity against phytohaemagglutinin-stimulated lymphoblasts of the stimulator was generated in the untreated MLC and also in the MLC of APC-depleted cell suspensions with endothelial cells added. It is concluded that arterial and venous endothelial cells can substitute for APC in the proliferative response of autologous lymphocytes against alloantigen and in the generation of CMC. Therefore, endothelial cells have an alloantigen-presenting capacity.