Upregulation of CD44 in the inflamed mouse air pouch injected with synthetic lipid A

OBJECTIVE: To investigate aspects of the inflammatory process of the mouse subcutaneous air pouch -- a facsimile synovial cavity -- induced by injection of lipid A, and to determine the expression and upregulation of CD44 in the lining cell layer of the inflamed air pouch. METHODS: Histological changes of inner walls in the mouse air pouch were evaluated 1, 3, and 7 days after injection of lipid A. RESULTS: Polymorphonuclear cell infiltration in the lining layer reached the maximum one day after injection of 10 microg of lipid A (10/10 mice in Grade 3; p < 0.01), while mononuclear cell infiltration and lining cell hyperplasia reached the maximum 3 days after injection (5/10 mice in Grade 2; 5/10 in Grade 3; p < 0.05; 39+/-11 layers, p < 0.05, respectively). The number of cell depth of CD44 positive lining layers and interleukin 1alpha (IL-1alpha) positive lining layers reached the maximum 3 days after injection (39+/-7 layers, p < 0.01; 35+/-12 layers, p < 0.05, respectively). CONCLUSION: These findings suggest that CD44 may have some connection with the proinflammatory cytokine IL-1alpha and induce inflammatory responses in the air pouch injected with lipid A.