Detection of deoxyribonuclease I along the secretory pathway in Paneth cells of human small intestine

The expression and distribution of deoxyribonuclease I (DNase I) in human duodenum, jejunum and ileum were examined by DNase I activity assay and the reverse transcriptase-polymerase chain reaction (RT-PCR), immunofluorescence, in situ hybridization, and immunocytochemical ultrastructural analyses. High levels of DNase I were detected in the cytoplasm of Paneth cells in human small intestine. A tissue homogenate fraction rich in Paneth cells showed strong DNase I-specific enzymatic activity. Immunofluorescence analysis using several specific anti-human DNase I antibodies showed very strong immunoreactivity in the cytoplasm of every Paneth cell. In situ hybridization demonstrated high levels of DNase I mRNA in Paneth cells. Immunogold electron microscopy revealed gold particles localized along the secretory pathway, with the exocrine secretory granules mostly labeled. Our findings strongly suggest that Paneth cells synthesize and secrete DNase I into the intestinal lumen.