Enhancement of Polymorphonuclear Cell Phagocytosis by Lipid A-Activated Monocytes Via Cell-to-Cell Contact: A Possible Role for Membrane-Associated Interleukin-6 and Interleukin-8

Polymorphs (PMN) and monocytes/macrophages (Mo) play a very important role in the host defence since they participate to inflammatory processes, tissue repairing and antitumor activity. Previous studies showed that lipopolysaccharide (LPS)-activated Mo are able to upregulate PMN phagocytic ability via cell-to-cell contact mechanisms mediated by bound to Mo membrane (m) cytokines (CKs), such as Tumor Necrosis Factor (TNF)-alpha, Interleukin (IL)-1 alpha and IL-1 beta. Based on these grounds, the role of Mo m-associated IL-6 and IL-8 on the modulation of PMN activity has been evaluated. In the first step, PMN incubated with lipid A (LA)-activated Mo showed an increased phagocytosis dependent on cell-to-cell contact only. In the second step, LA-activated Mo were pretreated with antirecombinant human (Rhu) IL-6 and IL-8 monoclonal antibodies (MoAbs), respectively and, in such a way, the enhanced phagocytic activity of PMN was abrogated. In the third step, PMN incubated with LA-activated supernatants (AS) from PBMC cultures exhibited an enhanced phagocytic activity, that was abrogated when LA-AS were pretreated with anti-Rhu IL-6 and anti-Rhu IL-8 MoAbs, respectively. These data suggest that IL-6 and IL-8 associated to Mo membrane may modulate PMN activation through a cell-to-cell contact dependent pathway.