HLA product expression and lymphocyte subpopulations in jejunum biopsies of children with idiopathic protracted diarrhoea and enterocyte autoantibodies.

Mature enterocytes from normal human small intestine express HLA Class II molecules, whereas the immature enterocytes of the crypts are devoid of these products. By the use of the Avidin/Biotin immunofluorescence technique, we examined HLA Class I and II expression on cryostat sections of jejunum biopsies from 10 children with idiopathic protracted diarrhoea (IPD) and circulating enterocyte autoantibodies (Ec-Abs). The results were compared with those obtained on gut specimens from nine children with protracted diarrhoea but no evidence of circulating Ec-Abs and from one child affected by gluten-sensitive enteropathy. HLA Class I expression was similar in control and pathological specimens but jejunum biopsies from children with IPD and high titres of Ec-Abs (greater than or equal to 1:64) showed 'inappropriate' Class II molecule expression in the crypt epithelial cells. This was in contrast with normal or only mildly increased Class II reactivity in the mature villi enterocytes. Conversely, jejunum biopsies from children with IPD but with low levels of Ec-Abs (less than or equal to 1:4) possessed a moderate but distinct decrease of Class II expression in mature enterocytes with a decreased number of CD3 and CD8 intraepithelial lymphocytes. It is speculated that quantitative and qualitative variations of HLA product expression in the gut epithelium of children with IPD could reflect the severity of the autoimmune process underlying the clinical picture and point to heterogeneities within the autoimmune enteropathy syndrome.