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Helminth infections at mucosal and tissue sites strongly polarize towards Th2 immune responses, following pathways which have yet to be elucidated. We investigated whether dendritic cells (DC) exposed to gastrointestinal nematodes induce Th2 differentiation and, if so, whether this outcome reflects the absence of DC activation (the default hypothesis). We studied secreted proteins from the parasite Nippostrongylus brasiliensis, which induce Th2 development in vivo without live infection. Murine bone marrow-derived DC pulsed with N. brasiliensis excretory/secretory antigen (NES) can, on transfer to naive recipients, prime mice for Th2 responsiveness. Heat inactivation of NES abolishes both its ability to drive Th2 responses in vivo and its capacity to stimulate DC for Th2 induction. NES, but not heat-inactivated NES, up-regulates DC maturation markers associated with Th2 promotion (CD86 and OX40L), with little change to CD80 and MHC class II. Moreover, DC exposed to NES readily produce IL-6 and IL-12p40, but not IL-12p70. LPS induced high IL-12p70 levels, except in DC that had been pre-incubated with NES. These data contradict the default hypothesis, demonstrating that a helminth product (NES) actively matures DC, selectively up-regulating CD86 and OX40L together with IL-6 production, while blocking IL-12p70 responsiveness in a manner consistent with Th2 generation in vivo.
Balic et al. (Mon,) studied this question.