Homing alone? CD18 in infectious and allergic disease

CD18 (integrin β2) is an adhesion molecule that is crucial for host defense, but a comprehensive understanding of CD18 in immunity has been elusive. Studies now show that, through the control of homing and other cellular adhesive events, CD18 is important for innate (especially neutrophil-dependent) immunity but not adaptive Th1 defense mechanisms. Furthermore, Th2 cells, which are associated with allergic disease and impair the clearance of Th1-dependent pathogens, require CD18 integrins for homing to sites of inflammation. These findings suggest that the therapeutic targeting of CD18 integrins to exclude the homing of pathogenic Th2 cells might be effective in the treatment of allergic and Th1-dependent infectious diseases.