CRITERIOS PARA EL REGISTRO Y PUNTUACIÓN DEL TEST

Savilahti and colleagues have reported on jejunal y/5+IEL numbers in patients with dermatitis herpetiformis, both treated and on a normal diet. Patients on a normal diet all demonstrated marked enteropathy, either subtotal or severe partial villous atrophy, similarly to the patients studied for this thesis. Patients with dermatitis herpetiformis had constantly increased y/ô+IEL numbers, regardless of the state of the intestinal mucosa or diet; fractional usage of the y/ô TCR was not commented on (Savilahti et al. 1992). Similarly, the patients with dermatitis herpetiformis studied for this thesis all had significant mucosal changes as did those studied by Marsh (Marsh 1989). This is contrast to a study of 82 patients with dermatitis herpetiformis from Edinburgh, 51 of whom were taking a normal diet of which 18 had no evidence of villous atrophy (Gawkrodger et al. 1991).

There seems to be few or no qualitative differences between the enteropathy of coeliac disease and that of dermatitis herpetiformis. The continuing challenge for investigators is to determine why some gluten sensitive individuals develop the characteristic skin lesions.

RECTAL St u d ie s

The data presented demonstrates T cell infiltration of the rectal mucosa in treated coeliac patients following a local gluten challenge, supporting previous observations by computerised-image analysis of 1pm toluidine blue stained sections (Loft et al. 1990; Loft et al. 1989). Consistent with the previous study, we found no significant difference in CD3+ lEL counts (i.e. total T cell count) between coeliac and control patients before challenge. The CD3+ lEL counts were in agreement with data published previously (Austin et al. 1988).

A study from Dr Marsh’s group of 65 patients with coeliac disease, did find a significant difference in CD3+ lEL numbers between the coeliac patients and controls, in contrast to their previous studies and this one (Ensari et al. 1993b). The reason suggested for this discrepancy, was that immunohistological measurements were

"better” than histological analysis because of the difficulty in assessing whether a particular cell is a lymphocyte or not, using histological methods. This does not explain the difference in results with the data presented here. Certainly in the coeliac patients there was a non-significant trend towards higher CD3+ lEL counts and it is possible that when a much larger group o f patients were studied this trend would be demonstrated to be a real effect, as the study of Ensari suggests. No significant difference was detected in y/0+ lEL numbers between pre-challenge coeliac patients and controls. In the larger study discussed above, a significant difference was detected and similarly, the trend towards higher y/5+ IEL counts seen in the data presented might become significant if a larger number of patients were studied.

After challenge, however, a rapid and significant rise occurred in CD3+ IEL in the coeliac patients, which was not matched by a rise in y/5+ IEL counts. This suggests that a/p+ IEL and not the y/5+ IEL are involved in the early mucosal response to local gluten challenge. The criticism of low patient numbers failing to detect a subtle effect is less tenable in this situation, since there was clearly a significant response in CD3+IEL numbers in the coeliac patients following FFIII. This finding obviously does not preclude a role for y/5+IEL in the pathogenesis of coeliac disease since it is clear that jejunal y/5+IEL numbers are increased in coeliac disease. The rate of infiltration of the mucosa by y/5+IEL, however, would appear to be delayed compared to that of a/p+IEL. It is possible, or even probable, that these cells are involved in the long term established coeliac lesion, given the evidence of their cytotoxic capabilties.

The data confirms and extends earlier work demonstrating that the rectal mucosa is abnormal in coeliac disease. It demonstrates the capability of the sensitised coeliac rectal mucosa to respond briskly to a luminal antigen challenge by the epithelial infiltration of CD3+ lymphocytes. Presumably the lack of coeliac toxic gluten peptides in the rectal lumen, because of proximal digestion and absorption, restricts the potential expresssion of colonic gluten sensitivity to a relative minority of coeliac patients. The rectal mucosa in coeliac patients is not usually exposed to coeliac toxic peptides and thus the infiltration by T cells following local gluten challenge is strong evidence of

y/ô T C ells in Gluten S en sitive Enteropathy

sensitised cells that are circulating, at least in the mesenteric territory. This is further evidence for T cell mechanisms playing a fundamental role in the pathogenesis of coeliac disease.

The role played by IEL, however, is difficult to interpret In Loft’s analysis of the same rectal gluten challenges, the IEL responses occurred after the initial events seen in the lamina propria, suggesting that they do not have a major role in initiating the mucosal lesion (Loft et al. 1989). This carefully timed study showed that lymphocytes initially appeared in vessels at 2 hr, emigrated into the lamina propria at 4-6 hr, and peaked in the epithelium some 6-8 hr post-challenge. The IEL response reached a maximum subsequent to the early-phase lamina propria response, and receded before the late-phase inflammatory response. Whatever the role of IEL in coeliac disease, the twofold increase in IEL 6 hr post-challenge did seem to be a good marker of gluten sensitivity. Further studies from Dr Marsh’s group have examined the time course of mucosal adhesion molecule expression following local rectal gluten challenge (Ensari et al. 1993a). Early rises within 4 hours were demonstrated for both E-selectin and VC AM in the lamina propria. ICAM-1 did not change significantly, perhaps due to a high level of constitutive expression in the rectal mucosa. This study provides further evidence of the importance of immunopathological events in the lamina propria of the intestine in coeliac disease.

Fu t u r e Dir e c t io n s

The demonstration of increased numbers of y/Ô+IEL in the intestinal mucosa of gluten sensitive patients has been an exciting discovery in the subject. Their role in the aetiopathogenesis of the disease however, still remains to be clearly defined. Useful information is most likely to come from further functional studies of cloned y/5TCR+ lymphocytes. In particular, the antigens they respond to, how such antigens are presented and by which cells, are questions to which studies should be directed. In dermatitis herpetiformis, since the intestinal lesion appears to be essentially identical to that of coeliac patients, it would seem sensible to direct studies at understanding the

pathogenesis of the skin lesion as a means of explaining the difference in the clinical expression of gluten sensitivity. Further dissection of the genetic factors contributing to the susceptibility to gluten sensitivity may also allow the two conditions to be differentiated.

Co n c l u s io n s

y/5+IEL are found in increased numbers within the intestinal mucosa of patients with coeliac disease and dermatitis herpetiformis. In distinction from some other studies, a correlation between y/5+IEL numbers and enteropathy was found, suggesting that they form a component part of the epithelial mucosal immune response to gluten in sensitive patients. The relationship between y/5+IEL numbers and enteropathy is complex however, since they do not seem to be involved in the early response to gluten challenge, at least in the rectal mucosa and in some individuals raised y/ô+IEL numbers are found in the absence of obvious enteropathy. It is possible that y/5+IEL subserve more than one function in the aetiopathogenesis of coeliac disease; there is strong evidence from functional studies that such cells are capable of cytotoxicity but other functions remain to be defined.

131

C h a p t e r 4 : G l i a d i n P e p t i d e T o x i c i t y i n C o e l i a c D i s e a s e

Introduction

Perhaps the most important enviromental factor associated with coeliac disease is the ingestion of toxic cereal products. The interaction between, what we presume to be a relatively short, cereal peptide and the host leads to the eventual clinical expression of the condition. Definition of the toxic peptide is thus of considerable importance to understanding the pathogenesis of coeliac disease.