Introduction:
The incidence of eosinophilic esophagitis (EoE) is rapidly increasing in both children and adults. However, despite extensive research, data on disease pathogenesis and useful markers for predicting treatment response are still lacking. The aim of the study was to analyze matrix metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinase-1 (TIMP-1) expression in the esophagus of pediatric patients with EoE.

Material and methods:
This single-center study included newly diagnosed children with EoE based on endoscopic and histopathological results, children with esophageal eosinophilia (EE) not meeting the EoE criteria and healthy controls. Immunohistochemistry for MMP-1 and TIMP-1 was performed.

Results:
Among the 30 children whose biopsy specimens were evaluated, 10 patients were diagnosed with EoE, 10 patients with EE and 10 were healthy controls. Weak expression of MMP-1 in esophageal samples was observed in half or more cases in each group. However, strong MMP-1 expression was noted in half of EoE patients before treatment with a decrease in number of cases after treatment. Interestingly, lack of TIMP-1 expression was noted in all EoE patients, in contrast to EE samples, or control cases. Children with strong MMP-1 expression at the time of EoE diagnosis appeared to respond less well to proton pump inhibitors (PPIs) either alone or in combination with an elimination diet. There were no differences in MMP-1 expression with PPI monotherapy as opposed to combination therapy.

Conclusions:
Our data revealed that children with EoE did not express TIMP-1 in esophageal tissue, unlike EE and healthy controls. More intense expression of MMP-1 at diagnosis was associated with a poor response to treatment.