Transforming growth factor-α (TGF-α) exerts several effects on target cells, such as neovascularization promotion and mitogenic signalling. Using immunoelectron microscopy, we show that monocytes and neutrophils, store TGF-α in cytoplasmic granules. In monocytes, TGF-α did not colocalize with components of peroxidase-positive granules or with albumin of secretory vesicles. Furthermore, no colocalization of TGF-α with components of azurophilic or specific granules or secretory vesicles was observed in neutrophils. Activated monocytes and tissue-macrophages contained much less TGF-α–positive granules, suggesting TGF-α release. Western blot analysis showed a protein of 10 kD in lysates of monocytes. TGF-α mRNA was detected in monocytoid cells from the bone marrow by in situ hybridization. This study shows for the first time that monocytes and neutrophils contain TGF-α in all stages of maturation and that TGF-α in monocytes is stored in a large population of peroxidase-negative granules suggesting a function for these granules. Monocytes and neutrophils are important effector cells in inflammatory reactions. The present finding that these cells contain TGF-α might explain complications such as fibrosis and neoplastic transformation, caused by chronic inflammation.

The murine CD18 monoclonal antibody (mAb) M18/2 was reported to inhibit lymphoma metastasis [Zahalka, M. A. et al. (1993) J. Immunol. 150, 4466]. To identify the pathways potentially blocked, we studied the effects of M18/2 compared with two new mAb against murine CD18, GAME-46, and -245. Whereas the GAME mAb blocked most Mac-1-mediated interactions, M18/2 had no effect, or even stimulated. The same was true for adhesion of LFA-1 to ICAM-1. To test effects on interactions with different ICAMs, we used L cells transfected with human ICAM-1, -2, and -3. As previously described, mouse LFA-1 does not bind to human ICAM-1 but we show here that mouse LFA-1 does bind to human ICAM-2 and -3. Again, the GAME mAb blocked completely, but M18/2 did not. These results indicate that the LFA-1 binding sites for ICAM-1 and ICAM-2 and -3, although in close vicinity, are distinct. Furthermore, effects of M18/2 on metastasis cannot be ascribed to blocking of any known beta2-integrin activity.

During the late-phase asthmatic response eosinophils and neutrophils infiltrate the lungs and cause severe damage. In this study, we investigated in vitro the migration of eosinophils, in the absence and presence of neutrophils, across a monolayer of lung H292 epithelial cells. The migration of eosinophils towards the complement fragment 5a (C5a) was increased when neutrophils were added to the upper compartment of the Transwells, and decreased when neutrophils were added to the lower compartment. Moreover, neutrophils exclusively stimulated eosinophil migration towards C5a, and not towards other chemoattractants such as RANTES, IL-8 or PAF. Neutrophils and eosinophils differed in that neutrophils, but not eosinophils, rapidly inactivated C5a, suggesting that neutrophils in the upper compartment remove part of the active C5a that has diffused into the upper compartment. Indeed, we found that the addition of other C5a-degrading agents, such as human serum or carboxypeptidase B, also enhanced eosinophil migration when added to the upper compartment and decreased migration when added to the lower compartment. Taken together, these results indicate that the presence of neutrophils influences the migratory behaviour of eosinophils in vitro. The neutrophils presumably maintain a proper C5a chemotactic gradient in the transmigration model, which results in enhanced eosinophil chemotaxis.