Assessment of mucosal integrity by quantifying neutrophil granulocyte influx in murine models of acute intestinal injury.

Intact epithelial body surfaces represent physical barriers which protect the organism from invading pathogens and loss of nutrients. Barrier malfunction is closely linked to disorders such as inflammatory bowel disease and graft-versus-host disease. In fact, several pharmacological or radiobiological therapeutic strategies have side effects that affect epithelial surfaces. In this context, assays that accurately assess epithelial barrier integrity in patients and animal models are crucial to create a better understanding of the mechanisms leading to disease or limiting therapeutic approaches due to barrier disruption. Here, we tested the ability of the widely used FITC-dextran intestinal permeability analysis to evaluate loss of intestinal barrier integrity in different murine models of gut mucosal damage and established influx of neutrophil granulocytes into the intestinal lamina propria (LP) as an alternative approach. We demonstrate that the sensitivity and specificity of FITC-dextran intestinal permeability analysis is relatively low: Although it did represent severe forms of mucosal damage due to intensive conditioning therapy (high doses of either total body irradiation (TBI) or chemotherapy) or after conditioning and allogeneic stem cell transplantation, it did not recognize less severe forms of damage as after lower doses of TBI or chemotherapy alone. In addition, discrimination of untreated from irradiated mice by differences in FITC-dextran translocation was not exact. In contrast, influx of neutrophil granulocytes into the intestinal LP, which reflects immune activation due to translocation of microbes and microbial products during intestinal barrier breech, quantitatively correlated with the severity of intestinal barrier damage. It accurately represented both severe and less severe forms of intestinal damage as after high or lower dose TBI or chemotherapy and correctly discriminated treated from untreated animals. Taken together, we demonstrate the limitations of FITC-dextran intestinal permeability analysis and identify intestinal neutrophil influx as a powerful additional tool to measure breakdown of intestinal barrier function.