MUC1 cell surface mucin is a critical element of the mucosal barrier to infection

Cell surface mucin glycoproteins are highly expressed by all mucosal tissues, yet their physiological role is currently unknown. We hypothesized that cell surface mucins protect mucosal cells from infection. A rapid progressive increase in gastrointestinal expression of mucin I (Muc1) cell surface mucin followed infection of mice with the bacterial pathogen Campylobacter jejuni. In the first week following oral infection, C jejuni was detected in the systemic organs of the vast majority of Mucl (-)/(-) mice but never in Muc1(+)/(+) mice. Although C jejuni entered gastrointestinal epithelial cells of both Mucl(-)/(-) and Mucl (+)/(+) mice, small intestinal damage as manifested by increased apoptosis and enucleated and shed villous epithelium was more common in Muc1(-)/(-) mice. Using radiation chimeras, we determined that prevention of systemic infection in wild-type mice was due exclusively to epithelial Mucl rather than Mucl on hematopoietic cells. Expression of MUC1-enhanced resistance to C. jejuni cytolethal distending toxin (CDT) in vitro and CDT null C. jejuni showed lower gastric colonization in Muc1(-)/(-) mice in vivo. We believe this is the first in vivo experimental study to demonstrate that cell surface mucins are a critical component of mucosal defence and that the study provides the foundation for exploration of their contribution to epithelial infectious and inflammatory diseases.