reticuloendothelial cells /ritik′yəlō·en′dōthē″lē·əl/ [L, reticulum + Gk, endon, within, thele, nipple] , albuminoid or scleroprotein cells lining vascular and lymph vessels and capable of phagocytosing bacteria, viruses, and colloidal particles or of forming immune bodies against foreign particles.