Humoral and cellular immune dysfunction in a patient with Bloom's syndrome and recurrent infections.

Immunological evaluation of a patient with Bloom's syndrome (BS) who suffered from recurrent bacterial and fungal infections, revealed low serum levels of IgG and high levels of IgM accompanied by an elevated proportion of surface membrane IgM positive B-lymphocytes and a decreased proportion of IgG positive B-cells. In vitro IgG secretion was also reduced whereas IgM production was normal. Although proportions of T-cell subsets were normal and proliferative responses to T-cell mitogens were adequate, a defective regulatory T-cell function for the generation of IgG was observed. Natural killer (NK) cell activity against K562 tumor cells was also decreased in this patient. The findings in this patient may suggest a maturation arrest of lymphocytes at an early developmental stage, and this may explain in part the increased susceptibility to infections.