Notch2 is essential for antiparasite immunity of mast cells in the intestine. N2-MxcKO or control Notch2^flox/flox mice were subcutaneously injected with third-stage infective larvae of S venezuelensis. (A) The number of mast cells per 10 vcus in the small intestine on day 8 after S venezuelensis infection. Data are presented as means ± SEM. The number of mast cells was much less in N2-MxcKO mice; n = 3, P = .008592 (total), P = .005695 (villus, epithelium), P = .000715 (villus, lamina propria), P = .005245 (crypt, epithelium), and P = .045466 (crypt, lamina propria). Note that mast cells in N2-MxcKO mice were abnormally clustered in the lamina propria, whereas most of those in the control Notch2^flox/flox mice were intraepithelially migrated. (B) Toluidine blue staining followed by eosin staining of the small intestine on day 8; original magnification ×200. (C) The number of mast cells per 10 vcus in the small intestine on day 13 after S venezuelensis infection. Data are presented as means ± SEM; n = 3, P = .026076 (villus, epithelium), P = .00194 (villus, lamina propria), P = .021177 (crypt, epithelium), and P = .019324 (crypt, lamina propria), P = .047445 (submucosa). (D) Toluidine blue staining followed by eosin staining of the small intestine on day 13. Original magnification ×200. (E) The total number of mast cells per 10 vcus on day 0, day 8, and day 13 of infection. The total number of mast cells was significantly lower in N2-MxcKO mice at the early phase (day 8) and almost equal at the later phase (day 13) to that of control mice. Data are presented as means ± SEM; n = 10 and 8 (day 0, Notch2^flox/flox and N2-MxcKO); n = 3 and 3 (day 8, Notch2^flox/flox and N2-MxcKO); n = 4 and 4 (day 13, Notch2^flox/flox and N2-MxcKO). (F) Time course of egg number in the stool. The number of excreted eggs was significantly greater in N2-MxcKO mice compared with those in Notch2^flox/flox mice. Data are represented as means ± SEM; n = 4; P = .0291 (day 8) and P = .0219 (day 9). (G) Hematoxylin-eosin staining of the small intestine on day 12. Original magnification ×200. Arrows indicate worms. Worms were still observed in the villi in the jejunum of N2-MxcKO, but not of Notch2^flox/flox mice.