Immunoblotting, in combination with high-resolution electrophoresis and the use of mouse monoclonal antibodies to human (sub)class immunoglobulin (Ig) isotypes, substantially increased the sensitivity with which homogeneous Ig components (H-Ig) could be detected. Using this technique, we reinvestigated 40 selected sera, previously found to be negative for H-Ig by agar electrophoresis and immunofixation, from two groups of individuals thought to have an age-related immunodeficiency, i.e., persons older than 95 years and recipients of kidney grafts who were undergoing immunosuppressive treatment. In both groups, small single or multiple H-Ig components were found, in frequencies of 76% and 79%, respectively. For comparison, the Ig spectrum of 10 sera from patients on dialysis treatment and of 33 sera from young adult blood donors was ordinarily heterogeneous, except for one elderly patient and one blood donor with a previously unknown IgG2 deficiency. These results are complementary to the observations in some immunodeficiencies in children and indicate that the appearance of single or multiple H-Ig components in low concentration can be considered a very sensitive indicator of certain immune system disorders forming a separate category of monoclonal gammopathies.

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