Hyper IgM with combined immunodeficiency.

This report describes a fourteen year old girl with an unusual immunodeficiency characterized by persistent lymphadenopathy and associated with hypogammaglobulinaemia, excessive IgM production and a severe T cell defect. Total T cell and T helper cell numbers were reduced and T cell proliferative responses to mitogens were poor. Serum IgM levels showed marked fluctuations and peaks correlated with acute tender lymphadenopathy. She was treated with intravenous gammaglobulin and prophylactic antibiotics. Although defective isotype switching of B cells into IgA and IgG producing cells has been accepted as the mechanism of the hyper IgM syndrome, it is becoming increasingly evident that T cell function is not uncommonly involved and may be responsible for impaired isotype switching.