Phenotypically immature IgG-bearing B cells in patients with hypogammaglobulinemia.

We investigated the prevalence of phenotypically immature IgG B cells (i.e., coexpressing surface IgG and IgM) in the peripheral blood of 12 patients with hypogammaglobulinemia and in normal individuals. Patients had ataxia-telangiectasia (N = 1), hyper-IgM combined immunodeficiency (N = 1), or common variable immunodeficiency (CVI). IgG/IgM-positive B cells were evaluated by two-color immunofluorescence using fluorescein- or rhodamine-conjugated goat antiserum; to minimize artifacts due to in vivo cytophilic binding of autologous IgG, cell-bound cytophilic Ig were eluted at pH 4 and Fc receptors were blocked by heat-aggregated rabbit IgG before fluorescent staining. All patients, except two with late-onset CVI, had markedly increased proportions of double-stained IgG B cells (56 to 100% of IgG-bearing B cells) in comparison with normal individuals (11 to 33%).