Analysis of gene expression in ceca of Helicobacter hepaticus-infected A/JCr mice before and after development of typhlitis

Abstract

The inflammatory bowel diseases, Crohn's disease and ulcerative colitis, are chronic inflammatory disorders of the gastrointestinal tract. The causes of these diseases remain unknown; however, prevailing theories suggest that chronic intestinal inflammation results from a dysregulated immune response to ubiquitous bacterial antigens. While a substantial body of data has been amassed describing the role of the adaptive immune system in perpetuating and sustaining inflammation, very little is known about the early signals, prior to the development of inflammation, that initiate and direct the abnormal immune response. To this end, we characterized the gene expression profile of A/JCr mice with Helicobacter hepaticus-induced typhlitis at month 1 of infection, prior to the onset of histologic disease, and month 3 of infection, after chronic inflammation is fully established. Analysis of the gene expression in ceca of H. hepaticus infected mice revealed 25 up-regulated and 3 down-regulated genes in the month-1 postinoculation group and 31 up-regulated and 2 down-regulated genes in the month-3 postinoculation group. Among these was a subset of immune-related genes, including interferon-inducible protein 10, monokine induced by gamma interferon, macrophage-induced protein 1 alpha, and serum amyloid A1. Semiquantitative real-time reverse transcriptase PCR confirmed the increased expression levels of these genes, as well as elevated expression of gamma interferon. To our knowledge, this is the first report profiling cecal gene expression in H. hepaticus-infected A/JCr mice. The findings of altered gene expression prior to the development of any features of pathology and the ensuing chronic disease course make this an attractive model for studying early host response to microbe-induced inflammatory bowel disease.

FIG. 1.

Photomicrograph of cecal sections from H. hepaticus-infected (B and D) and -naïve control (A and C) mice at months 1 (A and B) and 3 (C and D) postinoculation. (A, B, and D) No histologic lesions were identified in cecal sections from naïve control and month-1 postinfection groups. (C) Histologic lesions in the month-3 postinfection group were characterized by moderate mononuclear cell infiltrates and mild mucosal hyperplasia. Hematoxylin and eosin stain; bar = 60 μm.

FIG. 2.

The ceca were scored for intensity, longitudinal extent, and vertical extent of inflammation as well as hyperplasia at months 1 (A) and 3 (B) postinfection. (A) Median cecal lesion scores of naïve control and H. hepaticus-infected mice at month 1 postinfection were not statistically different. (B) Median cecal lesion scores of H. hepaticus-infected mice at month 3 postinfection were significantly increased compared to those of their age-matched cohorts. *, P < 0.05; Kruskal-Wallis, one-way ANOVA on ranks.

FIG. 3.

The mean number of MIP-1α (A), MIG (B), IP-10 (C), SAA1 (D), and IFN-γ (E) mRNA molecules relative to the number of HPRT mRNA molecules in the ceca of naïve control and H. hepaticus-infected A/JCr mice at months 1 and 3 postinoculation (PI). Data represent mean plus or minus standard error of the mean of 10 mice per group. Letters (a and b) represent statistically significant (P < 0.05) difference according to Student-Newman-Keuls, one-way ANOVA.