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Type II pneumocytes release chemoattractant activity for monocytes constitutively.

In the present investigation, we determined whether A549 cells, a type II pneumocyte cell line, might release mediators that are responsible for monocyte chemoattractant activity (MCA) constitutively. To test this hypothesis, A549 cell supernatant fluids were harvested and evaluated for monocyte chemotaxis. A549 cell supernatant fluids showed MCA in a time-dependent manner (P < 0.001). Checkerboard analysis of 24- and 72-h supernatant fluids showed that the activity was chemokinetic rather than chemotactic. Partial characterization of 24- and 72-h supernatant fluids revealed that the mediator was composed of lipid-soluble activity that was blocked by lipoxygenase inhibitors and trypsin-sensitive activity blocked by cycloheximide. Molecular sieve column chromatography identified four molecular weight peaks. Two of four peaks were blocked by anti-monocyte chemoattractant protein-1 (MCP-1) and anti-transforming growth factor-beta (TGF-beta) polyclonal antibodies. MCP-1 and TGF-beta were detected by enzyme-linked immunosorbent assay. Leukotriene B4 (LTB4) receptor antagonist attenuated the lowest-molecular-weight peak chemotactic response, and the concentration of LTB4 was high enough for chemotactic activity. These findings suggest that type II pneumocytes may modulate the recruitment of monocytes into the alveolar space by releasing MCP-1, TGF-beta, and LTB4 constitutively.