Serum IgD levels in individuals infected with the human immunodeficiency viruses (HIV) were studied as a means of monitoring the character and timing of B cell activation in individuals with this infection. Significantly increased levels of IgD were characteristic of homosexual mean who were HIV seropositive but asymptomatic or mildly symptomatic. The hyper IgD globulinaemia became progressively more pronounced in patients with increasingly severe infection and reached its most marked level in patients with AIDS-related complex (ARC). In ARC patients, IgD levels were increased 8.8-fold above normal which was disproportionately greater than the 2.4-fold increase in IgG, the 1.8-fold increase in IgA and the 1.6-fold increase in IgM. IgD levels declined in AIDS patients (although remained elevated compared to controls). The data suggest that an unusual type of B cell activation is responsible for the unique pattern of hypergammaglobulinaemia seen in this disease and that B cell activation occurs early in the pathogenesis of HIV infection, often before development of symptoms, and continues throughout the course of infection.
