PTX3 function as an opsonin for the dectin-1-dependent internalization of zymosan by macrophages

Pentraxin 3 (PTX3) is a tumor necro- sis factor and interleukin-1-stimulated gene that encodes a long PTX with proinflammatory activity. Here, we show that peritoneal macrophages de- rived from PTX3 transgenic (Tg) mice express higher levels of PTX3 mRNA than macrophages from wild-type (WT) mice, at basal level as well as upon stimulation with zymosan (Zy). Macrophages from Tg mice also showed improved opsonin-inde- pendent phagocytosis of Zy particles and the yeast form of the fungus Paracoccidioides brasiliensis. In the case of P. brasiliensis, an enhanced micro- bicidal activity accompanied by higher production of nitric oxide was also observed in macrophages from Tg mice. Using fluorescein-activated cell sorter analysis and reverse transcriptase-polymer- ase chain reaction, we demonstrated that basal level of Toll-like receptor-6 and Zy-induced dec- tin-1 expression was slightly but consistently higher in macrophages from Tg mice than in macrophages from WT mice. Recombinant (r)PTX3 protein binds to Zy particles as well as to yeast cells of P. brasiliensis and addition of rPTX3, to a culture of WT; derived macrophages containing Zy leads to an increase in the phagocytic index, which parallels that of Tg-derived macrophages, demonstrating the opsonin-like activity of PTX3. It is important that blockade of dectin-1 receptor inhibited the phagocytosis of Zy particles by WT and PTX3 Tg macrophages, pointing out the relevant role of dec- tin-1 as the main receptor involved in Zy uptake. Our results provide evidence for a role of PTX3 as an important component of the innate-immune re- sponse and as part of the host mechanisms that control fungal recognition and phagocytosis. J. Leukoc. Biol. 75: 000-000; 2004.