Primary progressive multiple sclerosis (PPMS) is clinically characterized by progression without remission or relapse, in contrast to relapsing forms of MS. Pathologic and imaging findings also indicate that PPMS differs from relapsing forms. Recent studies examining potential immunologic differences among MS forms suggest that cytokine and adhesion molecule expression profiles, but not chemokine receptor profiles, in PPMS patients resemble those in healthy controls more than those in patients with relapsing MS. However, the significance of these findings remains to be fully elucidated, and there is little additional evidence as yet of marked differences among MS forms based on immunologic characteristics. Of interest are the recent demonstrations that activated immune cells produce brain-derived neurotrophic factor (BDNF), a neuroprotective factor, in MS lesions, that BDNF receptors are located in MS tissue, and that glatiramer acetate (GA)-specific T cells produce BDNF irrespective of T helper cell Th1 or Th2 phenotype. These findings both support the concept of a protective inflammation in MS and suggest an additional mechanism of action for the clinical effects of GA therapy in MS. Whether and to what extent this mechanism is present in different MS forms remain to be clarified.