Serum IgD levels and infections in Down's syndrome

Immunology of Down syndrome: a review

Subjects with Down syndrome (DS) have a high mortality due to infections and a high risk of developing malignancies. These observations, together with the demonstration of a frequent occurrence of HBsAg carrier state and of autoantibodies, have prompted investigations of the immune function in DS. Thymic morphological and functional abnormalities have been demonstrated. Peripheral blood mononuclear cells of DS subjects have been shown to include a high number of T lymphocytes with low avidity for sheep erythrocytes and a very high percentage of cells with an NK phenotype. However, NK activity is low in DS. Production of some important cytokines, such as IL-2, is depressed, thus contributing to T-cell derangement. Abnormalities of the B-cell compartment were also demonstrated, with a tendency towards high IgG and low IgM serum levels. Controversial results have been obtained with regard to antigen-specific antibody response. Also phagocytes of DS subjects display some characteristic functional impairments, with low chemotactic ability and reduced production of oxygen radicals. Despite the clearly established and rather detailed evidence of immune derangements, therapeutic trials have been anecdotal and resulted in marginal effects. HBV vaccination is highly advisable in DS because of the high risk of becoming chronic HBV carriers once infected.

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.

On the influence of age on immunity in Down's syndrome

In 23 subjects of different ages with Down's syndrome a number of parameters of non-specific defense of humoral and cellular immunity were investigated. While in all age groups complement factors C3, C4 and C5 as well as phagocytosis and NBT indices were in the normal range, a dysgammaglobulinaemia increasing with age with a hyperglobulinaemia of the IgG, IgA and IgD types was found, sparing immunoglobulins IgM and IgE. In addition the transformation capacity of peripheral blood lymphocytes decreased with age. This is understood as the consequence of premature aging of the thymus-dependent immune system.