Maria Ling Lundström1*, Jonas Halfvarson2*, Maria Lampinen1, Ida Schoultz3, Lennart Bodin4,5 and Marie Carlson1 *The authors have contributed equally

Affiliates

1 Department of Medical Sciences, Gastroenterology Research Group, Uppsala University, Uppsala, Sweden. 2 Department of Medical Sciences, Unit of Gastroenterology, Örebro University, Örebro, Sweden. 3 Department of Medical Sciences, Faculty of Medicine and Health, Örebro University, Örebro, Sweden. 4 Department of Statistics, Örebro University, SE 701 82 Örebro, Sweden. 5 Institute of Environmental Medicine, Karolinska Institute, SE 177 77 Stockholm, Sweden.

Abstract

Background: Eosinophil granulocytes are involved in the pathophysiology of inflammatory bowel disease (IBD) but their role and interaction with other immune cells is not fully known. To explore this, twin studies can be useful, where previous studies have indicated a subclinical inflammation with increased neutrophil activity among healthy twin siblings of IBD patients.
Aims: To clarify if there is a subclinical eosinophil activity in healthy twin siblings in discordant twin pair with IBD and to assess the influence of genetics in this context.
Material and methods: Eosinophil derived neurotoxin (EDN) and eosinophil cationic protein (ECP) were analysed in faecal samples from discordant twin pairs with either Crohn’s disease (n=37) or ulcerative colitis (n=21) and then compared to healthy controls (n=44). For EDN and ECP, logistic regression was used and odds ratio (OR) with 95% confidence interval was calculated. Eosinophil peroxidase (EPO) was detected by immunohistochemistry in biopsies from rectum.
Results: Twins with Crohn’s disease displayed higher levels of EDN (OR 2.98 (1.65-5.37)) and ECP (OR 1.83 (1.24-2.70)) compared to their healthy co-twins as well as compared to external non-related healthy controls (OR 4.53 (2.39-8.66) and OR 1.71 (1.01-2.90), respectively). Consistently, higher levels of EDN (OR 2.43 (1.13-5.24)) and ECP (OR 1.53 (0.92-2.53)) were seen in twins with ulcerative colitis compared to their healthy co-twins and also compared to healthy controls (OR 2.62 (1.20-5.69) and OR 1.97 (1.04-3.74), respectively). No difference was observed between healthy twins and healthy controls, with respect to EDN or ECP levels. The number of eosinophils in rectum, stained with EPO, was significantly increased in twins with UC compared to their healthy co-twins (p<0.001).
Conclusions: Our findings indicate that genetic and environmental risk factors alone do not initiate the activation of eosinophils, since levels of active eosinophils were not increased in healthy twin siblings who were predisposed to IBD. The observed upregulation of eosinophils among diseased twins seems to be a consequence of the inflammation rather than a primary trigger of the disease. Further studies are needed to characterize the chain of early events that ultimately leads to IBD.