Clearance of apo Nph induces an immunosuppressive response in pro-inflammatory type-1 and anti-inflammatory type-2 MPhi

Nph are crucial for proper host defence. Paradoxically, they also contribute to pathology in various inflammatory diseases. Hence, apo of Nph and subsequent removal from inflamed sites is critical for resolution of inflammation. Apo Nph are recognised and cleared by MPhi, supposedly in a "silent" fashion. MPhi show large heterogeneity, comprising various subsets with different functional and biochemical properties. The contribution of these distinct populations to clearance of apo Nph is as yet unknown. Here, we investigated phagocytosis and subsequent functional responses of in vitro generated pro-inflammatory MPhi1 and anti-inflammatory MPhi2. Although only MPhi2 were capable of efficient Nph phagocytosis, we found that contact with apo Nph excerts immunosuppressive effects on both subsets, skewing them towards an anti-inflammatory state.