Mac-1 is stored in specific granules in granulocytes and monocytes. Appropriate stimuli, such as PAF, result in the expression of Mac-1 on the cell surface. Activated Mac-1 serves as a chemo-attractant. Prior to activation Mac-1 is quiescent and non sticky. Activation of Mac-1 may play a role in the recruitment of neutrophils to an inflamed site. Mac-1 knockout mice do not have an inflammatory defect.