THE ALPHA-3 CHAIN OF TYPE-IV COLLAGEN PREVENTS ACTIVATION OF HUMAN POLYMORPHONUCLEAR LEUKOCYTES

Our initial observation that type I collagen activates polymorphonucle ar leukocytes (PMN) prompted the testing of the activating potential o f type IV collagen. It was noted, however, that type IV collagen isola ted from bovine lens capsule did not activate PMN but rather prevented their stimulation by N-formylmethionyl-leucyl-phenylalanine, phorbol myristate acetate, or type I collagen. This observation led to the pre sent study, which demonstrates that the inhibitory effect of lens caps ule type IV collagen resides in the noncollagenous (NC1) domain of the alpha 3 chain and specifically in the region comprising residues 185- 203 of the NC1 domain of both the human and bovine molecules. Syntheti c peptides from the same region of the NC1 domains of the alpha 1, alp ha 2, alpha 4, and alpha 5 chains did not possess the inhibitory effec t seen with the alpha 3 chain. The sequence S-N-S (residues 189-191) i s unique to the peptide of the alpha 3 chain, and substitution of eith er serine with alanine abolishes the inhibition. Type IV collagen isol ated from the mouse Engelbreth-Holm-Swarm (EHS) tumor, a molecule that lacks the alpha 3 chain, did not prevent PMN activation but instead s timulated the secretion of elastase and type TV collagenase. Incubatio n of PMN with intact lens capsule type IV collagen or a peptide compri sing residues 185-203 of the alpha 3(IV) chain resulted in a and fold increase of intracellular cAMP, whereas, Ca2+ levels remained unchange d. Incubating PMN with forskolin or with dibutyryl-cAMP resulted in th e inhibition of O-2(-) production and degranulation by PMN, thus mimic king the effects of type IV collagen and the alpha 3(IV) 185-203 pepti de. The data suggest that type TV collagen, through its alpha 3 chain, down-regulates PMN activation and thus decreases the potential for da mage as these cells traverse the capillary wall. Our in vitro experime nts suggest that the higher the content of the alpha 3(IV) chain is in a basement membrane, the wider would be its capacity for self-protect ion.