Reduced IFNgamma production ability due to reduced IFNgamma mRNA expression in PBMCs is associated with an elevated serum IgE level in atopic patients.

Patients with the human genetic disorder ataxia-telangiectasia (A-T) are characterized by immunodeficiency and a predisposition to develop lymphoid malignancies. The gene mutated in A-T patients, ATM, codes for a high molecular weight protein that is implicated in DNA damage recognition and cell cycle control. The ATM protein does not change in amount or cellular distribution throughout the cell cycle or in response to DNA damaging agents. Because peripheral blood mononuclear cells (PBMCs) are largely in a state of quiescence and can be readily stimulated to enter a proliferative phase and because A-T cells exhibit growth abnormalities and senescence, indicative of a general intracellular defect in signalling, we chose PBMCs to examine the relationship of ATM to the proliferative status of the cell. We show here that ATM protein is present at low levels in freshly isolated PBMCs and increases approximately 6-fold to 10-fold in response to a mitogenic stimulus, reaching a maximum after 3 to 4 days. A similar, but delayed response, was evident in the presence of serum only. This increase in ATM protein was accompanied by an increase in ATM kinase activity. While expression of ATM protein increased during proliferation, ATM mRNA expression was unchanged in stimulated and unstimulated cells and there was no evidence for increased ATM protein stability in the phytohemagglutinin (PHA)-treated cells. In keeping with the reduced levels of ATM in quiescent cells, the extent of radiation-induction of the p53 pathway was significantly lower than in mitogen-stimulated cells. Basal levels of p21 were elevated in quiescent cells, and the response to radiation was negligible or reduced compared with proliferating cells over a 2-hour period. Overall, the data suggest that the increase in ATM protein in proliferating cells is due to posttranscriptional regulation and points to a role for ATM in more general signalling.

The specific defect that causes IgG2 deficiency, which is one of the primary immunodeficiencies, is unknown. Recently, it was shown that interferon‐γ (IFN‐γ) induces synthesis of human germline Cγ2 transcripts. In the authors’ previous study and the present one, peripheral blood lymphocytes (PBLs) of all five tested patients with IgG2 deficiency failed to produce enough IFN‐γ when stimulated with phytohaemagglutinin or concanavalin A although they produced a sufficient amount of interleukin‐2 (IL‐2). The low level of IgG2 production in pokeweed mitogen‐stimulated PBLs of four tested patients was improved by the addition of recombinant IFN‐γ. In this study, the amount of IFN‐γ messenger RNA showed various degrees of reduction in all five tested patients. Sequence analysis of the IFN‐γ coding regions and flanking regions revealed neither a point mutation nor a deletion for any of the patients. Thus the results suggest that the reduced expression of IFN‐γ messenger RNA may play an important role in the IgG2 deficiency of these patients.