MICROVASCULAR PERICYTES EXPRESS PLATELET-DERIVED GROWTH-FACTOR-BETA RECEPTORS IN HUMAN HEALING WOUNDS AND COLORECTAL ADENOCARCINOMA

The expression of platelet-derived growth factor-beta (PDGF-beta) rece ptors in the microvasculature of human healing wounds and colorectal a denocarcinoma was investigated. Frozen sections were subjected to doub le immunofluorescence staining using monoclonal antibodies (MAbs) spec ific for pericytes (MAb 225.28 recognizing the high-molecular weight-m elanoma-associated antigen, expressed by activated pericytes during an giogenesis), endothelial cells (MAb PAL-E), laminin, as well as PDGF-b eta receptors (MAb PDGFR-B2) and its ligand PDGF-B chain (MAb PDGF 007 ). Stained sections were analyzed by computer-aided imaging processing that allowed for a numerical quantification of the degree of colocali zation of the investigated antigens. An apparent background colocaliza tion, varying between 23 and 35%, between markers for cells not expect ed to co-localize was recorded This background could be due to limitat ions of camera resolution, to out-of-focus fluorescence, and to interd igitations of the investigated structures. In all six tumor specimens, co-localization of PDGF-beta receptors and PAL-E was not different fr om the background co-localization, whereas that of PDGF-beta receptors and high-molecular weight-melanoma-associated antigen was significant ly higher with mean values between 57 and 71%. Qualitatively, the same pattern was obtained in the two investigated healing wounds. PDGF-B c hain did not co-localize with either PAL-E or high-molecular weight-me lanoma-associated antigen, but PDGF-B chain-expressing cells were, how ever, frequently found juxtaposed to the microvasculature. The express ion of PDGF-beta receptors on pericytes in activated microvessels and the presence of PDGF-B chain-expressing cells in close proximity to th e microvasculature of healing wounds and colorectal adenocarcinoma is compatible with a role of PDGF in the physiology of the microvasculatu re in these conditions.