Activated cytotoxict cells (t lymphocytes) flag cells for destruction by macrophages differentiate into plasma cells that secrete antibodies bind to antigens that are presented by special proteins that occur on membranes of eukaryotic cells flag cells for destruction by megakaryocytes attack foreign cells directly by binding to an antigen-bearing cell, secreting proteins that perforate the foreign cell's membrane, and signaling the cell to undergo apoptosis.