Discussion

Macrophages represent a spectrum of activation states. At their extremes, these can be pro-inflammatory (M1) or anti-inflammatory (M2). M2-like macrophages are characterised by production of markers such as Ym1. Ym1 has previously been shown to be present in acute injury and act as an adjuvant for the Th2 and Th17 responses in nematode infections. In Trichuris muris infection, in a C57BL/6 mouse model, Ym1+ M2 cells appear in the colon from d10 post-infection. We hypothesised that, as a modulator of the immune and repair responses, neutralising Ym1 function in T. muris infection will result in increased susceptibility to the parasites and worsened gut pathology. To assess the function of Ym1 in the context of T. muris infection in the gut, Ym1 function was inhibited using a neutralising anti-Ym1 antibody both early (d0–d12 p.i.) and late (d12–d21 p.i.) in T. muris infection in C57BL/6 mice. Late, but not early, depletion of Ym1 function resulted in enhanced worm expulsion by d21 p.i.. Enhanced worm expulsion was mediated by a heightened Th2 response as indicated by parasite-specific serum antibody levels and cytokine data. Additionally, no difference in gut pathology was detected. These results are contrary to our original hypothesis that Ym1 is an adjuvant for the Th2 response and involved in wound repair, and may give new insight into the role of Ym1 in the context of intestinal inflammation