Activation of human polymorphonuclear cells induces formation of functional gap junctions and expression of connexins

During inflammatory responses activated polymorphonuclear cells (PMNs) adhere to each other and form clusters within the vasculature or injured tissues. We hypothesized that conditions that partially mimic the chemical environment of inflammatory foci induce the expression of functional gap junctions (GJs) between cultured PMNs.

Human PMNs were treated with bacterial lipopolysaccharide (LPS), TNF-a, LPS plus medium conditioned by LPS-treated endothelial cells (ECs) or TNF-a plus ECs conditioned medium. Gap junctional communication was evaluated with the dye coupling technique using a permeant and an impermeant GJ fluorescent dye and GJ blockers. The expression of connexins, GJ protein subunits, was evaluated by immunocytochemistry and immunoblotting. Cytochalasin-D and nocodazole were used to evaluate the involvement of cytoskeleton in the induction of dye coupling.

Treatment with LPS or TNF-a induced the formation of PMN aggregates, but cells were not dye coupled. If the latter protocols occurred in medium conditioned by LPS-treated ECs or resting ECs, respectively, intercellular transfer only of the GJ permeant molecule was observed in most clustered cells. Dye coupling was reversibly inhibited by GJ blockers and prevented by cytochalasin-D, a microfilament disrupter, but not by nocodazole, a microtubule disrupter. Treatments that induced dye coupling also induced connexin43 and connexin40, but not connexin32 immunoreactivity. None of these connexins was detected in circulating cells.

EC-derived factor(s) and microfilament integrity are required for dye coupling between LPS- and TNF-a-treated PMNs. GJ formation between PMNs is correlated with the presence of connexins 43 and 40, but not 32 and requires intact microfilaments.