Early deficit of lymphocytes in Wiskott-Aldrich syndrome: possible role of WASP in human lymphocyte maturation.

Wiskott-Aldrich syndrome (WAS) is an X-linked platelet/immunodeficiency disease. The affected gene encodes WASP, a multidomain protein that regulates cytoskeletal assembly in blood cells. Patients have recurring infections, and their lymphocytes exhibit deficient proliferative responses in vitro. We report an evaluation of peripheral blood lymphocytes of 27 WAS patients, aged one month to 55 years. Whereas NK cells were normal, a significant deficit of T and B lymphocytes was observed. The number of lymphocytes was already decreased in infant patients, suggesting deficient output. Both CD4 and CD8 T lymphocytes were affected; the decrease was most pronounced for naïve T cells. Naïve CD4 lymphocytes of patients showed normal expression of Bcl-2, and Ki-67, and normal survival in vitro, suggesting that their in vivo survival and proliferation are normal. The collective data suggest that the patients' lymphocyte deficit results from deficient output, likely due to abnormal lymphocyte maturation in the thymus and bone marrow. We propose that WASP plays an important role not only in the function of mature T lymphocytes, but also in the maturation of human T and B lymphocytes and that impaired lymphocyte maturation is central to the aetiology of WAS immunodeficiency.

A novel and rapid assay for the detection of neutralizing antibodies against interferon-beta.

There is evidence that neutralizing antibodies (NAB) have a negative influence on the clinical and magnetic resonance imaging effects of interferon-beta (IFNbeta) in multiple sclerosis (MS) patients. The current methods for NAB detection are restricted to specialized laboratories because they require a cell culture and sometimes a viral culture. Results are typically obtained after several weeks. Therefore, the development of a simple and rapid assay for the detection of NAB was sought. Whole blood samples from 28 NAB-positive patients and 110 NAB-negative patients (52 with IFNbeta and 58 without IFNbeta therapy) were incubated with IFNbeta 976 IU/mL for 24 hours. MxA protein levels--a specific marker of class I IFN bioactivity--were measured in paired samples with and without IFNbeta incubation and the difference in MxA levels was calculated. The mean increase of MxA levels after stimulation with IFNbeta in the NAB-positive group was 8 ng/mL (range 0-44 ng/mL) and in the NAB-negative group was 84 ng/mL (range 0-302 ng/mL). Using an increase of 22.5 ng/mL as cut-off) the specificity of the MxA stimulation assay was 81.2% and the sensitivity was 96.4%. The whole blood MxA stimulation assay is virtually as sensitive as the conventional NAB assay but somewhat less specific. However, this is outweighed by the procedural advantage of the assay, which is simpler, quicker and much less expensive.