The human type I Interferon (IFN) family includes 14 closely related cytokines that are produced in response to viral and bacterial infections and mediate the progress of innate immune responses to adaptive immune protection, bind to a common receptor, and have qualitatively similar biologic activities. We have shown previously that IFN-alpha2 can induce human T cell chemotaxis, suggesting that type I IFNs may contribute to the development of an inflammatory environment. We here report that, in addition to promoting T cell chemotaxis, IFN-alpha2 enhances T cell adhesion to integrin ligands, which is associated with integrin clustering on the T cell surface and enhanced conjugate formation with dendritic cells. These effects were prevented by inhibition of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K). As type I IFN receptor is ubiquitously expressed, this analysis was extended to other human leukocyte populations, including granulocytes and B cells. All leukocyte populations analyzed displayed increased chemotaxis, integrin clustering, and increased integrin-mediated adhesion following exposure to IFN-alpha2, revealing a broad-spectrum proinflammatory activity. These findings have obvious implications for the role of type I IFNs in the development of inflammatory responses leading to the initiation of adaptive immunity.