SUMMARYT helper cell type 1 (Th1) and type 2 (Th2) immune responses are characterized by a different pattern of cytokine expression following T-cell activation. Alterations of the ratio of Th1 to Th2 cells are important determinants of susceptibility to viral and parasitic infections, allergies, antitumour responses, and autoimmunity. In this work we bring new evidence for an effect of haptoglobin (Hp), a positive acute-phase protein, on T-lymphocyte functions. We show that Hp specifically interacts with both resting and activated CD4 þ and CD8 þ T cells. This specific binding results in a strong suppression of induced T-cell proliferation. In addition, Hp exhibits a strong in vitro inhibitory effect on Th2 cytokine release, while the production of interferon-g (IFN-g) and interleukin-2 (IL-2) is only slightly inhibited at high Hp doses. As a result, the presence of Hp promotes Th1 activation over Th2 activation in vivo as evidenced in Hp-deficient mice. Anti-CD3 monoclonal antibody injection indeed resulted in predominant IL-4 production in Hp À/À mice, in contrast to predominant IFN-g production in Hp þ/þ mice. We conclude that Hp plays a modulating role on the Th1/Th2 balance by promoting a dominant Th1 cellular response. This points to a role of acute-phase proteins in balancing immune responses.

No abstract

No abstract

No abstract

Background: Respiratory infections are major causes of morbidity and mortality, but determinants of susceptibility are poorly defined. We studied whether and to what extent immunologic and genetic factors are associated with increased susceptibility to respiratory infections. Methods: We evaluated the prevalence of IgA, IgM, IgG, and IgG subclass deficiencies, impairment in the antibody response against pneumococcal polysaccharides, G2m(n) allotypes, Fc␥RIIa polymorphisms, partial C2 and partial C4 deficiency, promoter polymorphisms in MBL2, and lymphocyte subset deficiencies in a control population and in consecutive children with recurrent respiratory infections. Results: IgA and/or IgG subclass deficiency was found in 27 of 55 patients (49%) and 6 of 43 controls (14%) (P ‫؍‬ 0.0006). An impaired antibody response to polysaccharides was found in 7 patients (19%) and in 0 of 37 controls (P ‫؍‬ 0.002). The Gm(n)marker was absent in 25 of 55 patients (45%) and 6 of 42 controls (14%) (P ‫؍‬ 0.009). The MBL2 variants O/O, A/O, and A/A occurred in 9, 14, and 32 of the 55 patients, respectively, and in 1, 19, and 23 of the 43 controls, respectively (P ‫؍‬ 0.05). There was no increase in the prevalence of partial C4 deficiency, C2 deficiency, lymphocyte subset deficiency, or Fc␥RIIa polymorphism in the patients compared to the controls. A combination of at least 2 immune defects was found in 31 of 55 patients (56%) and in 4 of 42 controls (11.6%) (P <0.0001). Conclusion: Specific antipolysaccharide antibody deficiency, IgA and/or IgG subclass deficiency, Gm(n) allotype, and MBL2 genotype are susceptibility factors for recurrent respiratory infections, and coexistence of sev-