Th1-type responses mediate spontaneous ileitis in a novel murine model of Crohn's disease

Abstract

We describe here the immunologic characterization of a new mouse strain, SAMP1/Yit, which spontaneously develops a chronic intestinal inflammation localized to the terminal ileum. The resulting ileitis bears a remarkable resemblance to human Crohn's disease. This strain of mice develops discontinuous, transmural inflammatory lesions in the terminal ileum with 100% penetrance by 30 weeks of age. The intestinal inflammation is characterized by massive infiltration of activated CD4+ and CD8alpha(+)TCRalphabeta(+) T cells into the lamina propria and is accompanied by a dramatic decrease in the intraepithelial lymphocyte CD8alpha(+)TCRgammadelta(+)/CD8alpha(+)TCRalphabeta(+) ratio. The results of adoptive transfer experiments strongly suggest that CD4+ T cells that produce a Th1-like profile of cytokines, e.g., IFN-gamma and TNF, mediate the intestinal inflammation found in SAMP1/Yit mice. In addition, pretreatment of adoptive transfer recipients with a neutralizing anti-TNF antibody prevents the development of intestinal inflammation, suggesting that TNF plays an important role in the pathogenesis of intestinal inflammation in this model. To our knowledge, these data provide the first direct evidence that Th1-producing T cells mediate intestinal inflammation in a spontaneous animal model of human Crohn's disease.

Figure 1

Segmental nature of inflammatory lesions in SAMP1/Yit mice. (a) Sequential transverse sections of small intestine show a relatively normal segment (right section) with intact villous mucosal architecture and a relatively thin muscular layer. The adjacent inflamed segment (left section) shows loss of villous architecture with luminal narrowing and a thickened muscular layer. ×40. (b) Longitudinal section through a Swiss roll of ileum (distal ileum is in center of the roll) showing discrete discontinuous areas of inflammation (arrows) with loss of villous architecture and thickening of the muscular wall. ×20. (c) Higher magnification of the inflamed ileum seen in b. Villi are completely absent in areas. The lamina propria and submucosa are expanded by an inflammatory infiltrate composed of PMNs and mononuclear cells. ×150. (d) Higher magnification of uninflamed mucosa between the two inflammatory foci seen in b. The villi are long and thin; the lamina propria has few lymphocytes; and there is no accumulation of leukocytes in the submucosa or base of the mucosa. The intestinal crypts contain Paneth cells (with prominent cytoplasmic granules) located only at the very base. All panels show staining with hematoxylin and eosin. ×225.

Figure 2

Histological characteristics of intestinal inflammation in SAMP1/Yit mice. (a) An early aphthous inflammatory lesion involving a Peyer’s patch. A pre-existing submucosal lymphoid aggregate is involved by a mixed inflammatory infiltrate of PMNs and macrophages. The epithelium overlying this lesion is infiltrated by PMNs and is focally eroded. ×80; inset, ×125. (b) Inflamed small intestinal mucosa showing partial villous blunting and epithelial phenotypic changes. Compared with normal uninflamed mucosa (Figure 1d), there are increased numbers of Paneth cells in the crypts and mucin-secreting goblet cells in the crypts and on the villi. ×200. (c) Transmural inflammation. PMNs and mononuclear cells infiltrate the full thickness of the muscularis propria to involve the serosal surface. ×200. (d) Mucosal granuloma. A collection of epithelioid histiocytes is present within the lamina propria between intestinal crypts. ×400. (e) Active inflammation. PMNs can be seen within the lamina propria, infiltrating between epithelial cells (“cryptitis”) and present in aggregate within a crypt lumen (“crypt microabscess”). ×200. (f) Basal plasmacytosis. The base of the inflamed mucosa contains numerous plasma cells, characterized by large cells with eccentrically placed cytoplasm and coarse nuclear chromatin clumping in a “clock face” pattern. All panels show staining with hematoxylin and eosin. ×800.

Figure 3

Analysis of surface marker expression by CD4⁺ T cells from MLN. CD4⁺ T cell–enriched MLN cells were harvested from 30-week-old AKR and SAMP1/Yit mice. Cells were analyzed for the expression of CD25, CD69, CD44, CD62L, and CD45RB (n = 8).

Figure 4

Severity of ileitis after adoptive transfer of unfractionated MLN cells. (a) Dose response of MLN cells from 30-week-old SAMP1/Yit mice, 6 weeks after transfer. (b) Time course of response to transferred MLN cells. SCID mice received 1 × 10⁶ AKR or SAMP1/Yit MLN cells. Data are presented as mean ± SEM (n = 12).

Figure 5

Severity of ileitis after adoptive transfer of CD4⁺ MLN cells. (a) Dose response of transferred CD4⁺ MLN cells from 30-week-old AKR and SAMP1/Yit mice, 6 weeks after transfer. (b) Time course of response to transferred CD4⁺ MLN cells. SCID mice received 1 × 10⁶ AKR or SAMP1/Yit MLN cells. Data are presented as mean ± SEM (n = 16).

Figure 6

Histological features of ileitis adoptively transferred to SCID recipients by CD4⁺ T cells from MLN of SAMP1/Yit or AKR mice. Disease was localized primarily to the ileum, but was also detectable in the duodenum. (a) Representative ileum from a SCID mouse 6 weeks after transfer of AKR control cells shows normal structure of the intestinal mucosa with mild infiltration of inflammatory cells. (b) Ileum from a SCID mouse 6 weeks after transfer of SAMP1/Yit cells shows severe mucosal damage with heavy infiltration of PMN and mononuclear cells.

Figure 7

Cytokine production by MLN cells from SAMP1/Yit mice and from SCID recipients of SAMP1/Yit MLN CD4⁺ T cells. MLN cells (1 × 10⁶/ml) were cultured with immobilized anti-CD3, and secreted IFN-γ and TNF were measured by specific ELISA. (a) Cytokine production from MLN isolated from 30-week-old AKR or SAMP1/Yit mice. (b) Cytokine production from SCID recipients 6 weeks after transfer of MLN CD4⁺ T cells from AKR or SAMP1/Yit mice. Data are presented as mean ± SEM (n = 18). ^AP < 0.01.

Figure 8

Anti-TNF antibody treatment of ileitis adoptively transferred to SCID recipients by CD4⁺ T cells from the MLN of SAMP1/Yit mice. SCID mice were treated with a single injection of anti-TNF or isotype control antibody prior to adoptive transfer of 1 × 10⁶ MLN CD4⁺ T cells from SAMP1/Yit mice. Severity of inflammation was evaluated 6 weeks after transfer using a semiquantitative scoring system. Black circle, mean; heavy black line, median; box, interquartile range; error bars, 95% confidence interval. ^AP < 0.01.