Publications

The emergence of monoclonal antibody technology has fostered new therapeutic strategies for people with autoimmune diseases. One of the most promising of these strategies involves the use of CD4 monoclonal antibodies, which are effective in animal models for systemic lupus erythematosus, diabetes mellitus, rheumatoid arthritis, myasthenia gravis, and multiple sclerosis. The appeal of CD4 antibodies is enhanced by several factors: (1) their effectiveness does not depend on depletion of target cells; (2) they may block the host immune response to therapy, and (3) they have been well-tolerated in preliminary human trials. The principal obstacle to the use of CD4 monoclonal antibodies stems from their adverse effects on normal immune function.

Interleukin-6 (IL-6/B cell stimulatory factor 2) has been found to drive activated human B-lymphocytes through the final stages of differentiation to become immunoglobulin-producing cells. Most patients with common variable immunodeficiency (CVI) have B-lymphocytes that fail to differentiate into high-rate immunoglobulin-secreting cells in vivo and in vitro. In view of (1) the known effects of IL-6 to promote B-lymphocyte terminal differentiation and (2) the defect in differentiation in B-lymphocytes of patients with CVI, we believed that it was important to analyze the role of this cytokine in patients with CVI. Using an IL-6-dependent murine hybridoma cell line in a bioassay, serum IL-6 levels were determined in 17 patients with CVI and in eight normal control subjects. Thirteen of the 17 patients with CVI exhibited serum IL-6 levels that were twofold to 18-fold higher than the range (mean, +2 SD) of normal control subjects. Spontaneous IL-6 production by peripheral blood mononuclear cells (PBMC) of patients with CVI was significantly higher than that from normal control subjects, whereas lipopolysaccharide maximally stimulated IL-6 production by PBMCs of patients with CVI or PBMCs of normal control subjects was equivalent. A substance inhibitory of IL-6 bioactivity was found in equivalent amounts in sera of both patients and normal control subjects. Sera from patients with CVI with high IL-6 bioactivity were found to have saturated this IL-6 inhibitory substance, thus resulting in large amounts of free IL-6 in the sera. These studies suggest that the failure of B cells from patients with CVI to terminally differentiate into high-rate immunoglobulin-secreting cells cannot be attributed to a decrease in the serum levels of IL-6 and that the increased circulating IL-6 levels in patients with CVI result from hyperproduction rather than decreased use of IL-6. The persistently elevated levels of IL-6 observed in some patients with CVI may secondarily result in the induction of the neoplastic and autoimmune phenomena associated with this disease.