Descripción de las actividades

The intestinal immune system may be particularly vulnerable to changes in the regulatory mechanisms preventing immunopathologic reactions, due to it being continuously involved in immune responses against a variety of antigens [81]. In vivo

and in vitro experiments suggest that IL10 plays a protective role in intestinal barrier

function [43], and has an essential role in controlling intestinal immune responses directed against enteric antigens [81].

The IL10 gene-deficient (Il10-/-) mouse is one example of a genetic-based colitis model

of IBD. This type of model is useful for studying the role of genetic susceptibility to colitis and the interaction between genes and the environment in colitis development. The Il10-/- mouse has the IL10 gene inactivated by targeted mutation [81]. It is a

commonly used, commercially available, rodent model of IBD. Il10-/- mice develop

intestinal inflammation throughout any part of the small and large intestine (enterocolitis) with many of the same biochemical, histological and physiological characteristics seen in IBD, although the colon is most affected [65, 81, 82].

The mechanisms that underpin intestinal inflammation development in these mice have been reviewed [75], and inflammation in Il10-/- mice is characterised by a lack of

regulatory T cell-derived IL10 suppression of TH1 responses, resulting in dysregulated IL12 production and dominant TH1 cytokine profiles with increased production of IFNγ

and TNFα [75]. Il10-/- mice have been widely used to study the role of the microbiota,

immune dysregulation and epithelial integrity in IBD pathogenesis.

A number of findings support the relevance of studying intestinal inflammation using the Il10-/- mouse model. In many genome-wide association studies in the human

population, polymorphisms of the IL10 gene have not been strongly associated with development of CD [83], although a systematic genome-wide analysis of UC has

Chapter 1: General introduction

19

Table 1.3 Examples of animal models of IBD. The categories are: (1) antigen-

induced colitis and colitis induced by the microbiota; (2) other inducible forms of colitis (chemical, immunological, and physical); (3) genetic-based colitis models (transgenic and gene-deficient models); and (4) adoptive transfer models; (5) spontaneous colitis models.

Species Mechanism of colitis induction Category Citation

Pig dextran sodium sulphate (DSS) 2 [84]

Rat dextran sodium sulphate (DSS) 2 [68]

Rat trinitrobenzenesulfonic acid (TNBS) 2 [69, 85]

Mouse Il10-/- gene deficient 1, 3 and 5 [75, 86]

Mouse keratin 8 gene deficiency 1, 3 and 5 [87]

Mouse dextran sodium sulphate (DSS) 2 [88]

[89]

Mouse deoxycholate 2 [90]

Mouse genetic defects in both TGF_{10R2 signaling} βRII and IL- 3 and 5 [91]

Mouse multi-drug-resistant (MDR1) gene

deficiency 3 and 5 [92]

Mouse CD45RBHiT cell transfer into CB-17 SCID

Chapter 1: General introduction

20 reported an association between UC and a single nucleotide polymorphism (SNP) immediately flanking the IL10 gene [94], and Il10 SNPs have been associated with

paediatric onset CD [95]. In addition, a CD-associated NOD2 mutation was shown to suppress transcription of the Il10 gene due to the inhibition of the activity of nuclear

ribonucleoprotein hnRNP-A1 by the 3020insC Nod2 mutant protein [96]. An effective therapy for CD (anti-TNFα therapy) also ameliorates inflammation in Il10-/- mice [74].

Defective IL10 signalling has been found to define a subgroup of patients with IBD [97]. These findings indicate that Il10-/- mice are a relevant model in terms of both

pathophysiology and genetic relevance to IBD.

The Il10-/- mice develop chronic enterocolitis that becomes apparent at 4-8 weeks of age

when raised in conventional animal care conditions (i.e. conditions that are not germ- free, or specific-pathogen-free (SPF)). Intestinal permeability and antibody responses to systemic endotoxaemia increase during the development of colitis in Il10-/- mice

(C57BL/6J background) [82]. Il10-/- mice also develop anaemia and growth retardation,

probably explained by disturbance of nutrient absorption as a result of the alterations in microstructure and physiology of the small and large intestine (C57BL/6J background, with 129/Ola influence from stem cells used to generate the knockout) [81]. The anaemia seen in Il10-/- mice seems to be caused by iron deficiency, with other factors

besides malabsorption probably contributing to the anaemia, such as overproduction of certain types of cytokines [81].

Exposure to micro-organisms has a major effect on disease progression in Il10-/- mice. Il10-/- mice housed in germ-free conditions do not develop any symptoms of intestinal

inflammation, whereas those in conventional and specific pathogen free (SPF) conditions do (C57BL/6J x 129/Ola background) [65]. Il10-/- mice housed in SPF

conditions have the same pathological changes in the proximal colon but different alterations in the duodenum and proximal jejunum compared to Il10-/- mice housed in

conventional conditions, and the disease takes longer to develop (with weight loss evident from 7 weeks of age in SPF conditions versus 3-4 weeks of age for conventional conditions) and is less severe [65, 81].

The natural progression of enterocolitis in Il10-/- mice in SPF conditions has been

characterised [98]. These mice have features reminiscent of the enterocolitis seen in human CD patients, but also exhibit some features atypical of CD (marked crypt

Chapter 1: General introduction

21 hyperplasia, rare occurrence of granulomas, fibrosis and lymphoid aggregates, and the absence of fissures, fistulae, and ileal inflammation). Enterocolitis in Il10-/- mice is

associated with uncontrolled production of pro-inflammatory mediators by macrophages and TH1-like cells including IL1α, TNFα, IL6, NO, and IFNγ[98].

Susceptibility to enterocolitis varies with background strain due to genetic differences. For example, C3H/HeJBir.Il10-/- mice are more susceptible than C57BL/6J.Il10-/- mice,

and a first generation cross of these two strains produces mice that develop an intermediate degree of enterocolitis, confirming that susceptibility is heritable [67, 99]. C57BL/6J.Il10-/- mice are more prone to developing rectal prolapses than

C3H/HeJBir.Il10-/- mice, and these can occur as early as 9 weeks of age, despite the

occurrence of faecal bleeding and diarrhoea in C3H/HeJBir.Il10-/- mice but not

C57BL/6J.Il10-/- mice [67]. Il10-/- mice on BALBc and 129 SvEv backgrounds develop

more severe colitis than those on the C57BL/6 background [98].