MAST-CELL DERIVED HEPARIN ACTIVATES THE CONTACT SYSTEM - A LINK TO KININ GENERATION IN ALLERGIC REACTIONS

Contact activation occurs when plasma comes in contact with negatively charged manmade surfaces but no substance that initiates contact acti vation in vivo has been identified. We have isolated a mast cell hepar in proteoglycan (MC-HepPG) from a Furth mouse mastocytoma-derived cell line that is analogous to human tissue-type mast cell HepPG. This mat erial and other glycosaminoglycans (GAGs) were tested for their abilit y to accelerate the reciprocal activation of factor XII and prekallikr ein and the autoactivation of factor XII. Quantitative analysis showed the MC-HepPG to be as active as dextran sulfate on a weight basis; ho g intestine heparin, dermatan sulfate, keratan polysulfate and chondro itin sulfate C were less active, other sulfated polysaccharides were e ssentially inactive. Incubation of MC-HepPG in 1:4 diluted plasma resu lted in complete cleavage of high molecular weight kininogen in a fact or XII-dependent reaction. All of the MC-HepPG dependent reactions des cribed above were inhibited by preincubation of MC-HepPG with heparina se I and II but not by pretreatment with heparitinase, chondroitinase ABC or the serine protease inhibitor aPMSF thus indicating that hepari n proteoglycan is indeed acting as an initiating 'surface'. We analyse d the proteoglycan preparation by HPLC gel filtration. Fractions spann ing a molecular weight range of >400 000-8000 were active initiators. Comparison of the chromatograms obtained before and after cleavage of GAG side chains from the protein core suggested that dissociated GAGs in the MW range 69 000-17 000 are the most active species rather than the complete proteoglycan. MC-HepPG GAGs therefore represent a physiol ogic macromolecule with activity comparable to non-physiological surfa ces in a purified system and with the capability to induce activation of the contact system in diluted plasma. Its ability to promote kinin generation links cellular and humoral inflammatory responses in the pe rivasculature and provides a possible explanation for the elevated kin in levels observed after allergen exposure.