Platelet-derived growth factor B-chain of hematopoietic origin is not necessary for granulation tissue formation and its absence enhances vascularization

The hypothesis that wound repair is augmented by delivery of platelet-deriv ed growth factor (PDGF) from platelets and macrophages is an attractive ext rapolation from the known activities of PDGF in cell culture and in vivo. T o test this hypothesis in mice, we prepared hematopoietic chimeras, in whic h the hematopoietic system of a normal adult mouse was replaced by the hema topoietic system of a PDGF B-chain -/- or +/+ donor. We initiated local gra nulation tissue formation either by implanting small surgical sponges to el icit a foreign body granulation tissue response, or by ligating the left co mmon carotid to form an organized thrombus. We found that the absence of he matopoietic PDGF B-chain did not decrease the extent of granulation tissue or vascular lesion formation, and that the vascularization of both lesions increased by similar to 100%. We conclude that PDGF B-chain from cells of h ematopoietic origin, including platelets and macrophages, is not important for granulation tissue formation, and that it reduces vascularization of gr anulation issue, probably through disabling of the short-range chemotactic gradients of PDGF that are important for recruiting pericytes/smooth muscle cells to the endothelium of new vessels.