In vitro studies on human IgD. III. Immunologic features of individuals with high sera IgD and spontaneous IgD biosynthesis.

The immunologic characteristics of normal persons with high sera IgD values were analyzed. Elevated sera IgD appeared to be the consequence of increased biosynthesis as reflected by an increased number of IgD-Ig-containing cells, an elevated sera IgD, lambda/kappa ratio, and increased spontaneous IgD secretion in vitro. These same findings have been previously linked to increased IgD production (S.D. Litwin and B.D. Zehr, Eur. J. Immunol. 17, 483, 491, 1987). Elevated sera IgD proved relatively stable over 21 months, in five selected individuals, favoring a genetic vs acquired explanation. The failure of sera IgG, IgA, and IgM to positively correlate with IgD weighed against polyclonal Ig synthesis. However, high IgD was inversely correlated to IgM class values and a high sera IgD subset of the population (greater than 31 micrograms/ml) had lower levels of certain IgM antibodies. Analysis of spontaneous IgD secretion, an event frequently encountered in high sera IgD persons, discloses 2/29 cultures with rising supernatant IgD implying in vitro induction. The results emphasize a role for active IgD biosynthesis in the immune responses of certain individuals.