β-Glucan Receptors on IL-4 Activated Macrophages Are Required for Hookworm Larvae Recognition and Trapping

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Recent advances in the field of host immunity against parasitic nematodes have revealed the importance of macrophages in trapping tissue migratory larvae. Protective immune mechanisms against the rodent hookworm Nippostrongylus brasiliensis (Nb) are mediated, at least in part, by IL-4-activated macrophages that bind and trap larvae in the lung. However, it is still not clear how host macrophages recognize the parasite. An in vitro co-culture system of bone marrow-derived macrophages and Nb infective larvae was utilized to screen for the possible ligand-receptor pair involved in macrophage attack of larvae. Competitive binding assays revealed an important role for β-glucan recognition in the process. We further identified a role for CD11b and the non-classical pattern recognition receptor ephrin-A2 (EphA2), but not the highly expressed β-glucan dectin-1 receptor, in this process of recognition. This work raises the possibility that parasitic nematodes synthesize β-glucans and it identifies CD11b and ephrin-A2 as important pattern recognition receptors involved in the host recognition of these evolutionary old pathogens. To our knowledge, this is the first time that EphA2 has been implicated in immune responses to a helminth.