Two immunologically distinct forms of late-onset hypogammaglobulinaemia.

Most patients with late-onset bypogammaglobulinaemia have normal numbers of B cells. In addition, some of these patients have been shown to have circulating T cells which suppress immunolobulin production in vitro. From our present studies on a large series of patients it appears that these two findings distinguish two separate groups of patients. The majority of the patients have circulating B cells which are 'immature' in the sense that they produce IgM but very little IgG or IgA in vitro. These patients also fail to produce IgA in vivo but their T cells show normal function in vitro and normal T cell markers. Patients with the second form of the disease, including those with associated thymoma, have very few circulating B cells, and relatively preserved IgA production in vivo. In our series it was only this minority of patients whose T cells showed abnormal markers and increased suppressor activity in vitro.