Schistosome larvae stimulate macrophage cytokine production through TLR4-dependent and -independent pathways

Exposure of the mammalian host to infective larvae of Schistosoma mansoni causes an acute inflammatory response in the skin and the activation of several cell types of the innate immune response including macrophages. Using an in vitro model of macrophage activation, we show that schistosome larvae possess molecules that directly stimulate both thioglycollate-elicited macrophages (tMφ) and IFNγ-activated tMφ in vitro to produce several cytokines including IL-6, IL-12p40 and IL-10. The parasite-derived molecules are enriched within the material released by the parasite following transformation [0- to 3-h released larval preparation (0-3hRP)] but not within soluble preparations of whole larvae. Cytokine production was maintained in the presence of polymyxin B, confirming that contaminating endotoxin was not responsible. IL-12p40 and IL-10 production was much lower by cells from C3H/HeJ mice, which have defective Toll-like receptor 4 (TLR4), but IL-6 production was unaffected. Experiments using TLR4^-/- mice confirmed that IL-12p40 production by tMφ in response to 0-3hRP was partly dependent upon functional TLR4, whereas IL-6 production was entirely independent. In contrast, tMφ from MyD88^-/- mice failed to secrete either IL-12p40 or IL-6, underlining a pivotal role of TLR signalling in cytokine production by macrophages in response to stimulation with 0-3hRP. Finally, we show that glycan components of 0-3hRP are required for optimal cytokine production since protease treatment of 0-3hRP had no effect on IL-12p40 production and only a slight effect on IL-6, while sodium meta-periodate treatment almost completely abolished production of both cytokines.