brasiliensis-infected Smarta/4get mice. The lack of Th2 cells in infected DO11/4get/Rag−/− or Smarta/4get mice does not formally exclude the possibility

that N. brasiliensis causes bystander activation of Th2 cells in a setting where antigen-specific T cells are present. To address this point we transferred CD4 T cells from DO11/4get/Rag−/− mice into normal 4get mice which were subsequently infected with N. brasiliensis. The transferred T cells did not differentiate into Th2 cells whereas T cells of the recipient mouse showed a normal Th2 response in lung and mesenteric lymph Bioactive Compound Library cost nodes (Fig. 5). The transferred T cells were not functionally compromised because infection with a mixture of N. brasiliensis and OVA resulted in efficient Th2 cell differentiation of the donor T cells while OVA administration alone did not induce Th2 polarization (Fig. 5). Taken together, these results demonstrate that bystander differentiation of naive T cells into Th2 cells does not occur even in the presence of a strong type 2 immune response and therefore we conclude that essentially all Th2 cells in N. brasiliensis-infected mice are parasite-specific

T cells. We could previously demonstrate that infection of mice Angiogenesis inhibitor with N. brasiliensis leads to accumulation of eosinophils and basophils in the lung28 and that this response could not be observed in Rag-deficient or MHC class II-deficient mice,29 suggesting that CD4 T cells are responsible for this effect. Furthermore, using an adoptive transfer system, we could previously show that IL-4/IL-13 from CD4 T cells was required for the IgE response whereas worm expulsion required IL-4/IL-13

from innate cells.29 To determine whether a reduced TCR repertoire would affect the efficiency of effector cell mobilization, IgE production and worm expulsion, we compared these three parameters in N. brasiliensis-infected 4get, DO11/4get and DO11/4get/Rag−/− mice. Eosinophils and basophils Morin Hydrate accumulated with comparable efficiency in spleen and lung of 4get and DO11/4get mice but no increase could be observed in DO11/4get/Rag−/− mice (Fig. 6a). Total serum IgE levels were strongly increased in both 4get and DO11/4get mice, which demonstrates that mice with a reduced TCR repertoire are still able to induce a profound polyclonal IgE response (Fig. 6b). Antigen-specific IgG1 response was detectable but significantly reduced in DO11/4get compared with 4get mice (Fig. 6c). Finally, worm expulsion was impaired in DO11/4get mice when compared with 4get mice, indicating that efficient immunity against this parasite requires a broad repertoire of TCR specificities (Fig. 6d). To further prove that a polyclonal T-cell population is required for protective immunity, we reconstituted Smarta/4get mice with 107 polyclonal naive CD4 T cells from 4get mice. The N.