Chikungunya fever is an arbovirosis of major impact in public health in Asia and Africa. Chikungunya (CHIK) virus is member of the genus Alphavirus and belongs to the Semliki Forest (SF) antigenic complex. We describe for the first time a panel of monoclonal antibodies (MAbs) reactive to CHIK envelope E2 glycoprotein. For the screening of E2-specific MAbs, we expressed a recombinant soluble CHIK E2 protein in Drosophila S2 cells. Analyzed by immunological methods, MAbs 3C3, 3E4, and 8A4 were selected on the basis of their reactivity. Their epitopes are located to the outer surface of CHIK virion. These MAbs have no cross reactivity with related members of SF antigenic complex with the notable exception of Igbo-Ora virus. Anti-CHIK E2 MAbs 3C3, 3E4, and 8A4 should be helpful for studying the biology of CHIK virus and pathogenesis of disease. The combination of 8A4 and 3E4 is suitable for developing a specific antigen-capture ELISA.

The development of anti-factor VIII (FVIII) antibodies (Abs), also called inhibitors, is currently one of the most serious complications arising during the treatment of hemophilia A patients. Improved prevention and eradication of these Abs remain a challenge both for clinicians and scientists. Numerous studies in the literature have reported on their epitope specificity, on their mechanism of FVIII inactivation, as well as on the methods used for their detection. In this review, we summarize the current knowledge on the nature (isotypes, kinetic properties), epitope properties, and mechanisms of action of anti-FVIII Abs. Furthermore, we present methods for detection and epitope characterization of anti-FVIII Abs with emphasis on the Luminex technique susceptible to facilitate the monitoring of changes in the epitope specificity of these Abs.

Summary The occurrence of alloantibodies against Factor VIII (FVIII) is the main iatrogenic complication in haemophilia A (HA). Anti‐FVIII autoantibodies may also spontaneously appear in non‐HA patients, leading to acquired haemophilia A. In both contexts, the antibody response against FVIII is complex and difficult to analyse due to the lack of suitable tools. Our purpose was to comprehensively map, at the amino acid level, discontinuous epitopes of the C2 domain of FVIII targeted by patients’ antibodies. We synthesized 33 synthetic peptides, which were predicted by the bioinformatic algorithm PEPOP to mimic C2 domain discontinuous epitopes. Using an inhibition assay based on the x‐MAP technology, we evaluated their ability to block the binding to the C2 domain of anti‐C2 domain antibodies from pooled plasma samples. Nine peptides were thus selected and tested again in individual plasma samples. Our results support the view that C2 domain epitopes are organized as an epitopic mosaic distributed around the molecule, showed that each patient displayed a specific anti‐C2 epitopic profile, and confirmed the complexity and variability of the immune response against the C2 domain of FVIII. This ability to finely map epitopes could be further used to follow the antibody specificity modifications over time.

Summary.  Background:  Acquired hemophilia A (AHA) is a severe life‐threatening autoimmune disease due to the development of autoantibodies that neutralize the procoagulant activity of factor VIII (FVIII). In rare cases, AHA occurs in the postpartum period as a serious complication of an otherwise normal pregnancy and delivery. Due to its rarity, little is known about the features of the antibody response to FVIII in AHA. Objectives:  Our study wanted to (i) determine the epitope specificity and the immunoglobulin (Ig) subclasses of anti‐FVIII autoantibodies in plasma samples from a large cohort of AHA patients, and (ii) compare the epitope specificity of anti‐FVIII autoantibodies in plasma samples from postpartum AHA and other AHA patients. Patients/Methods:  Seventy‐three plasma samples from patients with postpartum AHA (n = 10) or associated with malignancies (n = 16) or autoimmune diseases (n = 11) or without underlying disease (n = 36) were analyzed with three multiplexed assays. Results and Conclusions:  Our results showed a stronger response against the A1a1‐A2a2‐B fragments of FVIII and more specifically against the A1a1 domain in patients with postpartum AHA than in the other AHA groups (P < 0.01). Moreover, although IgG4 was the predominant IgG subclass in all groups, anti‐A1a1‐A2a2‐B and anti‐A1a1 domain autoantibodies of the IgG1 and IgG3 subclasses were more frequently detected in postpartum AHA than in the other AHA groups. These findings support the involvement of the Th1‐driven response in the generation of autoantibodies in women with postpartum AHA compared with the other groups of AHA patients in whom production of Th2‐driven IgG4 was predominant.