Animal models of inflammation induced by gene disruption

Dominant negative N-cadherin mutants

Cadherins are transraembranous glycoproteins that mediate cell adhesion. The cytoplasmic domain of N-cadherin includes a |3-catenin which, in turn, binds an a-catenin. The catenin-cadherin complexes regulate a variety of cell functions, including proliferation, polarity and migration. Disruptions of these interactions result in the development of IBD that closely resembles Crohn's disease. Chimeric mice, generated from normal blastocysts and genetically manipulated embryonic stem (ES) cells, have been used to study N-cadherin function. These B6<-»129 SV chimeric mice have patches of ES cell-derived, as well as the normal B6-derived, crypt villous units. The ES cell lineage is distinguished from the B6 cells by their ability to bind to Ulex europeus agglutinin type 1. Promoters are available that specifically express genes localized to the intestinal epithelium. ES cells transfected with such a promoter, the fatty acid binding promoter (Fabpi), linked to the negative cadherin (NCAD) was used to generate B6«->129 SV NCAD chimeras. Expression of the dominant mutant resulted in loss of endogenous E-cadherin, cell-to-cell adhesion and promoted early entry of epithelial cells into programmed cell death. E-cadherin is normally localized to the basolateral surface of intestinal epithelial cells and apical junctional complexes. Changes, confined to the intestine covered by the ES cell-derived epithelium (which expresses

NCAD) include lamina propria infiltration with lymphocytes and histiocytes, immunoglobulin A (IgA)-and IgG-secreting plasma cells and increased expression of class II major histocompatibility complex (MHC). By 3 months of age, crypt distortion and crypt abscesses appear. Chimeras expressing NCAD along the entire crypt villous axis have greater disease than those with NCAD expression confined to the villous epithelium. In these animals, intestinal dysplasia and neoplasms can also be seen. This animal model exemplifies the importance of the epithelial barrier in the prevention of IBD.

IL-2 knockout mice

Interleukin-2 (IL-2) activates macrophages, lympho-kine-activated killer (LAK) cells and natural killer (NK) cells and induces differentiation of B cells, in addition to promoting growth and expansion of T cells. In a study of the function of IL-2 in mice by gene disruption, it was noted that these mice develop a lesion that is similar in many ways to ulcerative colitis. IL-2 knockout mice develop normally until 4 weeks of age. Approximately half die after the first month of age, mainly from anemia, while those surviving more than 10 weeks develop a pancolitis characterized by bloody diarrhea and rectal prolapse. Colonic wall thickening, ulceration, crypt distortion and abscesses are seen on histological examination. Immune abnormalities in the lamina propria include an increase in activated T cells (as demonstrated by markers for CD44 and CD69), in activated B cells and in MHC class II expression, suggesting both T and B cells are stimulated in the colonic immune response. No bacterial pathogen has been identified but germ-free animals do not develop disease, suggesting that an abnormal immune response to enteric flora contributes to the pathogenesis of IBD.

IL-10 knockout mice

Derived from T cells, macrophages and certain B cells, IL-10 is a potent inhibitor of macrophages and Th1 lymphocytes. IL-10-deficient mice, generated by gene disruption in ES cells, develop intestinal disease resembling IBD, with both small and large intestinal involvement. The enterocolitis is segmental and associated with a chronic inflammatory infiltrate. Loss of epithelial integrity is also present, and there is an increase in class II MHC expression. The disease is ameliorated, but not eradicated by housing mice in a pathogen-free environment, as focal proximal colitis is still evident. Resolution, however, occurs on administration of IL-10 antagonists, suggesting that an aberrant TH1 cell response, normally inhibited by IL-10, may be responsible.

T cell receptor and MHC class II mutants

Chronic colitis resembling human ulcerative colitis is observed in mice that do not express normal T cell receptors on the T cell surface resulting from an introduced mutation in the p chain. In contrast, disruption in the recombinant activating gene RAG1, which results in animals lacking both B and T cells, does not result in bowel inflammation. Increased B cell activation is observed in the T cell receptor mut-atn mice with an increase in IgA, IgM and IgG secretion, perhaps due to a lack of T cell-mediated suppression of B cells. MHC class II_/ mice which lack class II-restricted CD4+ T cells also develop bowel inflammation, again implicating a loss of immunoregulatory T cells in the development of the disease. The mice with these lesions predominantly exhibit colonic disease. Histological sections show mucin depletion, crypt distortion and a mixed inflammatory histology. Ulceration, granulomas and fibrosis are not seen. The incidence and severity of the disease vary with the genetic background of the mice examined, implying that other genes modify disease susceptibility.

Gc*|2 knockout

G protein heterodimers of a, (3 and y chains serve as mediators of signal transduction for numerous surface receptors. Gai2 is widely distributed in intestinal epithelial cells and in lymphocytes. Its functions include activation of MAP kinase, stimulation of tumor necrosis factor a (TNFa) and production of colony-stimulating factor 1. Mice with an introduced deletion of Cai2 develop pancolitis by 8-12 weeks of age. Approximately a third of the animals develop adenocarcinoma by 15-33 weeks of age. There is an increase in CD44 T cells, and B cells. Unlike the knockouts of IL-2, IL-10 and the T cell receptor, pathogen-free mice continue to develop a pancolitis; however, variation in genetic background affects disease susceptibility.

How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book

Post a comment