LFA-1 (CD11a/CD18) is a member of the β2-integrin family of adhesion molecules important in leukocyte trafficking and activation. Although LFA-1 is thought to contribute to the development of experimental autoimmune encephalomyelitis (EAE) primarily through its functions on effector T cells, its importance on other leukocyte populations remains unexplored. To address this question, we performed both adoptive transfer EAE experiments involving CD11a-/- mice and trafficking studies using bioluminescent T cells expressing luciferase under the control of a CD2 promoter (T-lux cells). Transfer of encephalitogenic CD11a-/- T cells to wild type mice resulted in a significant reduction in overall EAE severity compared to control transfers. We also observed, using in vivo imaging techniques, that CD11a-/- T-lux cells readily infiltrated lymph nodes and the CNS of wild type recipients with kinetics comparable to CD11a+/+ transfers, although their overall numbers in these organs were reduced. Surprisingly, transfer of encephalitogenic wild type T cells to CD11a-/- mice induced a severe and sometimes fatal EAE disease course, associated with massive T cell infiltration and proliferation in the CNS. These data indicate that LFA-1 expression on leukocytes in recipient mice plays an important immunomodulatory role in EAE. Thus, LFA-1 acts as a key regulatory adhesion molecule during the development of EAE, serving both pro- and anti-inflammatory roles in disease pathogenesis. © 2008 Elsevier B.V. All rights reserved.