The blood system of vertebrates carries out an essential and versatile function, and it is only appropriate that blood cells evolve to be equally complex, with many specialized cell types. Red blood cells, or erythrocytes, are the most abundant and are hemoglobin-rich for oxygen transport. Platelets or thrombocytes and function in clotting and wound healing. White blood cells, or leukocytes, generally provide defense and are comprised of further specialized cells. Monocytes differentiate into macrophages and dendritic cells and function in phagocytosis, cytokine production, and antigen presentation. Lymphocytes are involved in adaptive immunity and its members can directly eliminate pathogens and tumor cells, or produce cytokines and antibodies. T helper cells, cytotoxic T cells, B cells, and natural killer cells are some of the subtypes of lymphocytes. Neutrophils use cytokine receptors to migrate to sites of infection or inflammation and attack infections. Eosinophils and basophils also play roles in fighting infection, but are notably associated with allergic responses. To help in choosing the right blood cell product, simply check the desired cell type, tissue, or species.