Acquired agammaglobulinemia after a life-threatening illness with clinical and laboratory features of infectious mononucleosis in three related male children.

Three males in one family (two siblings and one maternal cousin) had an illness with cervical adenopathy, hepatosplenomegaly, and a fulminant febrile course. In the two survivors agammaglobulinemia developed. One of them became ill at the age of six months and had an Epstein-Barr-virus antibody titer of 1:10 during illness and convalescence. The white-cell count was 120,000 with 90 per cent lymphocytes, most being atypical and forming increased numbers of sheep erythrocyte rosettes. IgM was elevated, IgA normal and IgG decreased. Subsequently, all immunoglobulins were absent, and the Epstein-Barr-virus antibody titer became negative. Peripheral B-cell number remained normal, but abnormal lymph-node architecture associated with failure to respond to antigenic challenge indicated B-cell dysfunction. The pathogenesis of this entity may involve an abnormal T-cell response to transformation of B cells by Epstein-Barr virus, leading to B-cell dysfunction and agammaglobulinemia.