ACCESSIBLE HYALURONAN RECEPTORS IDENTICAL TO ICAM-1 IN MOUSE MAST-CELL TUMORS

Immunohistochemical studies of the hyaluronan (HA)-receptor (R), origi nally found on liver endothelial cells (LEC) and related to the interc ellular adhesion molecule 1 (ICAM-1), showed that polyclonal antibodie s against HARLEC (HA receptor on LEC) also stain structures in mouse m astocytomas, mainly vessels. To test if intravenously administered HA might target the tumour receptors in vivo, mice carrying an inoculated mastocytoma in one hind leg muscle were injected in the tail vein wit h I-125-tyrosine (T)-labelled HA and killed 75 min after injection whe n organs and tissues were checked for radioactivity. When doses exceed ing the binding capacity of the liver were injected, a significant inc rease in radioactivity (up to five-fold) within the tumour tissue was found. The weight adjusted difference between control and tumour tissu e was greater for smaller tumours, probably due to necrosis in the lar ger. HA-staining of tumours from animals receiving I-125-T-HA, showed HA in areas that also stained weakly for ICAM-1 using monoclonal antib odies. ICAM-1 staining was dramatically increased after hyaluronidase treatment of the sections, indicating that the HA is bound to these re ceptors and thereby blocks antibody recognition.