During this prospective 1-year study, we used flow cytometry to measure changes in plasma microparticles (PMP) bearing CD31 (PMPCD31+), CD146 (PMPCD146+), and CD54/ICAM-1 (PMPCD54+) in 16 consecutive patients with relapsing-remitting MS (RRMS) before and after 3, 6, and 12 months of subcutaneous therapy with interferon-beta1a (44 micrograms, 3X weekly). Here, MCAM is linked to relapsing-remitting multiple sclerosis.