Interleukin-2 binding proteins in sera from normal subjects and multiple sclerosis patients.

We previously reported elevations of interleukin 2 (IL-2) in the serum of patients with chronic progressive MS. Using gel chromatography, protein A sepharose affinity chromatography, and ELISAs for IL-2 and the IL-2 soluble receptor, we now demonstrate that this cytokine is bound to serum proteins. These serum proteins include antibodies to IL-2, soluble IL-2 receptors, and high-molecular-weight proteins. Using a CTLL cell assay, a serum fraction corresponding to IgG antibodies to IL-2 inhibited the activity of this cytokine. Thus, we present evidence for potential immunomodulation of a pivotal cytokine in MS by serum proteins.