Activated eosinophils in adult coeliac disease: evidence for a local release of major basic protein.

The eosinophil population is increased in the jejunal mucosa of patients with coeliac disease. Eosinophils may participate in the mucosal damage by releasing their granule components that have cytotoxic properties such as eosinophil cationic protein (ECP) and major basic protein (MBP). This study aimed to assess the presence of ECP and MBP in the jejunal mucosa of 10 adult patients with active coeliac disease who presented with villous flattening. Endoscopic jejunal biopsy specimens were obtained from macroscopically flattened jejunal mucosa and were processed for ultrastructural study and immunogold labelling using anti-MBP, anti-ECP, and anti-IgA antibodies. Numerous eosinophils were found in the upper part of the lamina propria and showed two types of morphological change: some were lytic and others exhibited ultrastructural signs of activation, containing altered granules with fading of the central core. IgA plasma cells were intermingled with eosinophils and had dense deposits on the external side of their cytoplasmic membrane. MBP was detected in central cores of granules but also diffusely in their matrix and in tight association with dense extracellular deposits. Conversely, ECP was detected only in the matrix of eosinophil granules. This study showed that numerous eosinophils are in an activated state in the mucosa of patients with active coeliac disease and release cytotoxic proteins such as MBP, which could contribute to the mucosal damage. The observation that eosinophils and IgA plasmocytes were closely associated in the mucosa supports a role for IgA in eosinophil recruitment and activation in coeliac disease.