To identify overlapping and non-overlapping functions for TSP-1 and αvβ6, we crossed TSP-1-null and β6-null mice and compared the phenotype of the double-null mice with those of wild-type and single-null mice. The double-null mice exhibited focal acute and organizing pneumonia that was more severe than the wild-type and single-null mice as well as a significantly higher incidence of inflammation in tissues other than the lung. The TSP-1-null and β6-null mice exhibited a five to eight-fold increase in granulocyte recruitment to the lung three days after exposure to lipopolysaacharide. They also had abnormalities that were infrequently observed in the wild-type and single-null mice, including heart degeneration (8.35% in wild-type and 28.1% in double-null mice), hyperplasia of the glandular epithelium of the stomach (2.8% in wild-type and 21.1% in double-null mice) and endometrial hyperplasia (0% in wild-type and 38.5% in double-null females). Furthermore, the β6-null and double-null mice displayed a significant elevation in benign and malignant cancers. Stomach papillomas, squamous cell carcinomas of the ear and stomach, and adenocarcinomas of the lungs, vagina/cervix and colon were observed with the highest frequency. These data demonstrate that TSP-1 and αvβ6 are involved in regulation of the immune system and epithelial homeostasis. They also indicate that αvβ6 functions as a tumor suppressor gene and that activation of TGFβ by TSP-1 and αvβ6 contributes to normal tissue architecture and function.