The development of inhibitory antibodies against factor VIII (FVIII) (inhibitor) is the major complication in haemophilia A patients. The FVIII-binding antibodies development comprises a polyclonal immunoglobulin (Ig) G response. Recent studies showed strong correlation between the presence of neutralizing anti-FVIII antibodies (inhibitors) and IgG4 subclass. The aim of this study was to evaluate anti-FVIII IgG subclasses in haemophilia A patients with inhibitor both in a cross-sectional and in a longitudinal analysis. Inhibitors were determined by Nijmegen-Bethesda assay. Anti-FVIII IgG subclasses were performed by ELISA, and samples from 20 healthy individuals were used to validate the test. We studied 25 haemophilia A patients with inhibitor, previously treated exclusively with plasma-derived FVIII concentrates or bypassing agents. The IgG subclasses distributions were evaluated in two groups of patients classified according to inhibitor response. IgG1 and IgG4 antibodies were most prominent in haemophilia A patients with inhibitors when compared with IgG2 and IgG3. This study reports for the first time the behaviour of FVIII-binding IgG1 and IgG4 subclasses in a longitudinal analysis, in a clinical setting, of high-response inhibitor haemophilia A patients, showing the correlation of IgG4 and the inhibitor titres. In spite of being considered a non-pathologic antibody subclass with anti-inflammatory properties in other situations, IgG4 is correlated with the presence of high-titre inhibitor in the haemophilia setting. The comprehension of the IgG4 role in immune response may be crucial to establish the process for designing specific tolerance to FVIII.

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In contrast to haemophilia B, allergic manifestations are rare complications in haemophilia A (HA) patients treated with factor VIII (FVIII) concentrates. Nevertheless, it can be serious and hamper replacement therapy in these cases. The aims of this study were to evaluate the frequency of allergic reaction in a cohort of HA patients treated only with plasma-derived FVIII (pdFVIII) concentrates, and assess the possible immune mechanisms involved. History of allergic reaction was retrospectively assessed. Patients with allergic manifestations were followed, and had plasma samples collected in different timepoints in relation to the allergic episode. These samples were analysed for the presence of inhibitor and anti-FVIII immunoglobulins subclasses. Three of 322 HA patients (0.9%) developed allergic reaction after exposure to pdFVIII products during the last 15 years in our centre. The first patient, with severe HA, without inhibitor, had anti-pdFVIII IgE and IgG4, but no anti-recombinant FVIII (rFVIII) IgE. The second patient, with severe HA, and high-responding inhibitor, presented allergic manifestation with both, pdFVIII concentrate and activated prothrombin complex concentrate. Although anti-pdFVIII and anti-rFVIII IgG4 were detected, no anti-FVIII IgE was present. The third patient, with moderate HA without inhibitor, atopic, had no anti-FVIII immunoglobulin detected, and allergic symptoms disappeared after switching to rFVIII concentrate. This study corroborates the low incidence of allergic reactions in HA patients. In the three cases presented, the anti-FVIII immunoglobulin profile demonstrated that the allergic manifestation was triggered by other proteins contained in pdFVIII products, and not directed to FVIII.

These data suggest that the T allele of the CYBA C242T polymorphism may be used as a marker for adverse metabolic features in Brazilian subjects with systemic hypertension.