Background The generation of high-affinity antibodies requires the presence of a population of CD4+ T cells (follicular TH TFH cells) in the lymph node follicles. These cells differ from TH 1, TH 2, ...and TH 17 effector cells in that they strongly express activation markers and the chemokine receptor CXCR5 and secrete large amounts of IL-21 and CXCL13. Small numbers of nonactivated CD4+ CD45RO+ CXCR5+ T cells are also found in the blood. Objective We sought to obtain in vitro a population close to the TFH cells and to study the presence of this cell population among patients with autosomal dominant hyper-IgE syndrome carrying heterozygous signal transducer and activator of transcription 3 (STAT3) mutations that impair the IL-21 signaling required for B-cell differentiation. Methods CD4+ CD45RO+ CXCR5+ T cells were isolated from blood and activated by CD3/T-cell receptor. Results We found that CD4+ CD45RO+ CXCR5+ activated T cells corresponding to circulating bona fide memory TFH cells and that STAT3-deficient patients have abnormally low numbers of “TFH -like” blood T cells. However, STAT3-deficient TFH cells have much the same phenotypic and functional characteristics as TFH cells from healthy control subjects. The ability of STAT3-deficient TFH cells to produce IL-21 on CD28/T-cell receptor activation and to proliferate did not differ from that observed for control TFH cells in vitro . Although the STAT3-deficient TFH cells were also able to help control B cells to produce IgG and IgA, induction of IgG production by naive B cells was impaired. Conclusion Heterozygous mutations in STAT3 lead to reduced numbers of circulating TFH -like cells, a finding that might account (at least in part) for the observed defect in antibody production.
Background Primary immunoglobulin deficiencies lead to recurrent bacterial infections of the respiratory tract and bronchiectasis, even with adequate immunoglobulin replacement therapy. It is not ...known whether patients able to secrete IgM (eg, those with hyper-IgM HIgM syndrome) are as susceptible to these infections as patients who lack IgM production (eg, those with panhypogammaglobulinemia PHG). Objective This study is aimed at identifying specific microbiological and clinical (infections) characteristics that distinguish immunoglobulin-substituted patients with PHG from patients with HIgM syndrome. Methods A cohort of patients with HIgM syndrome (n = 25) and a cohort of patients with PHG (n = 86) were monitored prospectively for 2 years while receiving similar polyvalent immunoglobulin replacement therapies. Regular bacterial analyses of nasal swabs and sputum were performed, and clinical events were recorded. In parallel, serum and saliva IgM antibody concentrations were measured. Results When compared with patients with PHG, patients with HIgM syndrome were found to have a significantly lower risk of nontypeable Haemophilus influenzae carriage in particular (relative risk, 0.39; 95% CI, 0.21-0.63). Moreover, patients with HIgM syndrome (including those unable to generate somatic hypermutations of immunoglobulin genes) displayed anti–nontypeable H influenzae IgM antibodies in their serum and saliva. Also, patients with HIgM syndrome had a lower incidence of acute respiratory tract infections. Conclusions IgM antibodies appear to be microbiologically and clinically protective and might thus attenuate the infectious consequences of a lack of production of other immunoglobulin isotypes in patients with HIgM syndrome. Polyvalent IgG replacement therapy might not fully compensate for IgM deficiency. It might thus be worth adapting long-term antimicrobial prophylactic regimens according to the underlying B-cell immunodeficiency phenotype.
