Neutrophil tissue inhibitor of matrix metalloproteinases-1 occurs in novelvesicles that do not fuse with the phagosome

The human neutrophil granule location of precursors of matrix metalloprotei nases (MMPs), MMP-8 and -9, has been established, but that of the tissue in hibitor of matrix metalloproteinases-1 (TIMP-1) has not. In this study, lab eling for TIMP-1, pro-MMP-8, pro-MMP-9, and established granule marker prot eins reveals that TIMP-1 is mainly located in distinct oval, electron trans lucent organelles, a little larger than azurophil granules. A lack of label ing for the fluid phase endocytic marker, bovine serum albumin-gold, the ly sosome-associated membrane protein markers, and for glycosylphosphatidylino sitol-linked proteins, which are enriched in secretory vesicles, indicates the nonendosomal, non-lysosomal, and non-secretory nature of this organelle . Density gradient cofractionation with the least dense, secretory populati on and some pleomorphism of the organelle suggest it is a "vesicle" rather than a "granule" population. Colocalization with pro-MMP-9 or pro-MMP-8, in minor subpopulations, suggests that TIMP-1 vesicle biogenesis occurs betwe en metamyelocytic and terminal differentiation and before secretory vesicle synthesis. Pulse-chased IgG-coated latex beads and immunolabeling show tha t specific and azurophil granules fuse with the phagosome whereas TIMP-1 an d pro-MMP-9-containing organelles do not. This suggests that these play no role in phagosomal destruction of IgG-opsonized bacteria. Separate localiza tion and colocalization of these proteins may, however, facilitate fine reg ulation of extracellular proteolysis.