[Immunoglobulin D. Physiology and pathology excluding myeloma].

Immunoglobulin D is the fourth class of immunoglobulins secreted by the plasma cells and also, in 5% of lymphocytes, this is a surface immunoglobulin. Its serum levels are about 0.03 mg/ml, due to low secretion, intersititial diffusion and intense catabolism. IgD migrates on electrophoresis in the beta-gamma zone, on immuno-electrophoresis, in the beta2 zone. Only one disulphide bridge links the delta-chains together. The light chains, are, in most cases, lambda chain. Studies of the antigenic characteristics of the delta-chains are in progress. IgD does not take up complement, but has an antibody function. 37% of healthy subjects have anti IgD antibodies. Only 4 cases of monoclonal IgD gammopathy without malignant myeloma, have been reported. Anto-antibodies of IgD nature have been described in various connective tissue diseases or auto-immune processes.