Selective IgM deficiency: a case study.

We experienced an 85-year-old male patient with selective IgM deficiency. The average levels of his serum immunoglobulins were as follows: IgG, 1,165 mg/dl, IgA 280 mg/dl, and IgM 17 mg/dl. The subpopulations of peripheral blood lymphocytes in this patient were normal, including normal numbers of IgM-bearing lymphocytes. Normal amounts of cells with cytoplasmic IgM were induced by in vitro addition of pokeweek mitogen, and no inhibitory cells or inhibitory factors for in vitro production of IgM were demonstrated in his blood. These results suggest that some defects similar to those in patients with selective IgA deficiency may play a role in the development of selective IgM deficiency.