Fig. 2.

Schematic representation of CD47-signal regulatory protein-alpha (SIRP-α) interaction in relation to natural expression of SIRP-α on pig pulmonary macrophages. Left: In the organ-source pig, there is a normal inhibitory signal of porcine CD47 (in this example expressed on platelets) that is recognized by porcine SIRP-α. Center: After pig lung xenotransplantation, there might be a lack of recognition of human CD47 by porcine SIRP-α, resulting in phagocytosis of human platelets. (Some binding between SIRP-α and CD47 occurs, but there is a deficiency in signaling that prevents signal transduction, the cause of which is uncertain.) Right: Transgenic expression of human SIRP-α on pig pulmonary macro-phages would result in recognition of human CD47 on human platelets, thus inhibiting phagocytosis.