novo Th2 differentiation in vitro. As shown in Fig. 1 B and Fig. S1 D, in naive CD4+ cells the absence of SOCS2 re- sulted in a significantly higher frequency of Th2 cells (CD4+ IL-4+ cells; P < 0.001), thus indicating that SOCS2 must control polarization toward the Th2 lineage. Because parasitic helminth Schistosoma mansoni eggs in- duce a potent Th2 response (Fallon and Mangan, 2007), we used this model to compare Th2 responses in vivo in SOCS2/ mice relative to WT animals. SOCS2/ and WT mice were injected intraperitoneally with 10,000 S. mansoni eggs and, 10 d later, splenocytes were restimu- lated with anti-CD3/CD28 or with schistosome soluble egg antigen (SEA). Both approaches induced marked type 2 responses in WT mice relative to PBS-challenged mice (Fig. 1 C). Moreover, there was significantly (P < 0.05) greater production of the type 2 cytokines IL-4, IL-5, and IL-13 by splenic T cells from egg-injected SOCS2/ mice relative to WT mice after both nonspecific and antigen- specific TCR stimulation (Fig. 1 C). Interestingly, spleno- cytes from egg-injected SOCS2/ mice also produced significantly lower amounts of IL-17 compared with WT mice (Fig. 1 C). To specifically enumerate the in vivo ex- pansion of Th2 cells, S. mansoni eggs were injected into the footpads of SOCS2/ and WT mice. After 10 d, the fre- quency of Th2 (CD4+ IL-4+) cells in the popliteal LN was significantly higher (P < 0.001) in SOCS2/ mice than in WT animals (Fig. 1 D).To confirm that SOCS2 deficiency in CD4+ T cells was directly responsible for the observed Th2 bias, naive SOCS2/ or WT CD4+ T cells were transferred into JEM Vol. 208, No. 7 A r t i c l e Figure 2. SOCS2/ mice develop more severe AD than WT mice. (A) Calcipotriol (MC903) or ethanol was applied daily to the right ear of WT and SOCS2/ mice (n = 6 per group) and ear thickness was measured daily. (B) Representative pictures of H&E-stained ear sections from WT and SOCS2/ mice at the end of study (bars, 150 µm). (C) Quantitation of ear eosinophil infiltrates from 10 sections ran- domly selected out of one representative mouse per group. (D) Three mice per group were sacri- ficed at day 5, and auricular draining LN and spleen cells were isolated and restimulated in triplicate for 48 h with anti-CD3 and anti-CD28. Secreted cytokines were then measured by ELISA. Data are representative of three indepen- dent experiments and are presented as mean and SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001. RAG-1/ recipients and challenged with S. mansoni eggs. 10 d after injec- tion, the number of Th2 (CD4+ T1/ ST2+) cells in popliteal LN was signifi- cantly (P < 0.05) higher in mice re- constituted with SOCS2-deficient T cells when compared with those reconsti- tuted with WT cells (Fig. 1 E), show- ing a requirement for SOCS2 expression in CD4+ T cells in controlling in vivo differentiation of Th2 cells.These obser- vations indicate that SOCS2 deficiency unexpectedly favors Th2 polarization in vitro and in vivo and, therefore, that SOCS2 is a key regulator of Th2 differentiation. SOCS2/ mice are more susceptible to AD Atopic disorders are driven by an elevated Th2 response; therefore, we used an in vivo model of AD, which was pre- viously described by Li et al., (2006), to assess whether SOCS2/ mice are more susceptible to atopy. Mice were treated daily with an application of the vitamin D3 analogue calcipotriol (MC903). Topical application of MC903 trig- gered an AD-like response—increase in skin thickness—in all mice, but SOCS2/ mice exhibited earlier onset and more severe disease (Fig. 2 A). Histological examination showed red scaly lesioned skin, accompanied by epidermal hyperplasia with dermal lymphocyte infiltration that was more abundant in SOCS2/ mice (Fig. 2 B). Furthermore, the dermal inflammation was associated with a marked eosinophilic infiltrate that was significantly exaggerated in the SOCS2/ mice (P < 0.05; Fig. 2 C). Finally, analysis of cytokine secretion in restimulated auricular LN and spleen cells showed en- hanced IL-4, IL-5, and IL-13, but not IFN-, levels from MC903-treated SOCS2/ compared with treated WT ani- mals (P < 0.05; Fig. 2 D). All together, the data demonstrates that SOCS2/ mice were more susceptible to AD in this model, confirming an inhibitory effect of SOCS2 on the al- lergic response in vivo. 1525