LPS-induced stimulation of phagocytosis in the sipunculan worm Themiste petricola: possible involvement of human CD14, CD11B and CD11C cross-reactive molecules.

Coelomocytes of Themiste petricola, a marine invertebrate of the phylum Sipuncula, were exposed in vitro to bacterial lipopolysaccharides (LPS), and the phagocytic activity against heat-killed yeast (Saccharomices cerevisiae) was evaluated using a flow cytometric assay. An increase of phagocytic activity was observed following pre-incubation of coelomocytes over 20 h with either 5 micrograms/mL LPS or 1.5 micrograms/mL phorbol 12-myristate 13-acetate (PMA). The phagocytic enhancement induced by LPS was blocked by co-incubation with polymixin B, a ligand for the lipid A region of LPS. In a 72 h stimulation assay, LPS was also found to enhance phagocytosis. The enhancement was significantly higher when coelomocytes were incubated with LPS plus coelomic plasma. Using mAbs directed against human CD14 and components of the human LFA-1 complex, we identified coelomocyte surface antigens cross-reactive with CD14, CD11b and CD11c. The expression of CD11b and CD11c antigens was augmented by LPS treatment of coelomocytes. By double fluorescence assays, using mAb Leu-M3 and fluorescein labeled yeast, phagocytic coelomocytes were found to be mainly anti-CD14 positive. No cross-reactions were detected with mAbs against CD11a and CD18. Enzymatic treatment of coelomocytes with phosphatidyl inositol phospholipase C (PI-PLC) reduced the expression of the CD14-like antigen. The presence, in sipunculan coelomocytes, of antigens cross-reactive with CD14, the alpha chain of CR3 and of p150,95 raises the possibility that molecules related, although not necessary homologous, to the mammalian counterparts may have a role in the defense systems of these animals.