IMMUNOHISTOCHEMICAL LOCALIZATION OF DIFFERENT LAMININ ISOFORMS IN HUMAN NORMAL AND ADENOMATOUS ANTERIOR-PITUITARY

BACKGROUND: Laminin (LM) is an integral component of basement membrane s (BM), with important roles in various aspects of cell biology. Sever al different isoforms of LM have been described, and each comprises a molecule consisting of three subunit polypeptides, the A, B1, B2, Mor S chain. EXPERIMENTAL DESIGN: The distribution of different LM subunit s was studied in human nontumoral anterior pituitaries obtained postmo rtem and in pituitary adenomas by immunocytochemical methods using spe cific monoclonal antibodies. RESULTS: In normal tissue, the A, B1, and B2 chains had a ubiquitous localization in both parenchymatous and va scular BMs and in the pericapillary connective tissue space also. The S chain seemed to have principally a vascular localization, in contras t to the M chain that was mostly localized in the parenchymatous BM. T he same antigens were investigated in 23 human pituitary adenomas of d ifferent secretory type, grade and invasiveness. In all cases, the fiv e monoclonal antibodies gave a positive staining. The presence or the localization of LM chains did not display a specific pattern in the ad enomas according to their secretory type, grade or extent of local inv asion. In the adenomas, the anti-A, -B1, and -B2 monoclonal antibodies stained the stroma and in particular the vascular BMs as well as the sparse elements of parenchymatous BMs when they were present. The stai ning with anti-S antibody was localized in the stroma and around all t he blood vessels. In contrast, the immunoreactive material to anti-M a ntibody was associated to the sparse fragments of parenchymatous BMs a nd it delineated the boundary of adenoma cells and stroma. Within the stroma, the anti-M antibody immunoreactivity was regularly associated with the arterial walls but rarely with the venule walls. CONCLUSIONS: The human normal and tumoral anterior pituitary express all five LM s ubunits and thus contain several LM isoforms with different patterns o f localization. The most striking difference between the human normal and tumoral anterior pituitary concerns the peculiar expression of LM isoforms by adenomatous neovessels.