Serum IgD levels in mice: effect of strain, age and autoimmune disease.

Serum IgD levels were studied in mice. Strain-related variability of serum IgD levels was noted, and advanced age was associated with markedly increased IgD levels in a large percentage of mice from all strains. Strains prone to spontaneously arising autoimmune disease had elevated IgD levels; in NZB mice this was already present very early after birth (one week), whereas in MRL mice the elevated serum IgD levels were first seen somewhat later (3 months). In contrast, mice with collagen type II (CII)-induced autoimmune arthritis had no increase in serum IgD. Injection of the immunomodulating agents LPS and complete Freund's adjuvant (CFA) did not have a significant effect on serum IgD levels, but IL-1 induced a significant decrease in IgD.