Marginal zone B cells are critical to factor VIII inhibitor formation in mice with hemophilia A

Abstract

Although factor VIII (FVIII) replacement therapy can be lifesaving for patients with hemophilia A, neutralizing alloantibodies to FVIII, known as inhibitors, develop in a significant number of patients and actively block FVIII activity, making bleeding difficult to control and prevent. Although a variety of downstream immune factors likely regulate inhibitor formation, the identification and subsequent targeting of key initiators in inhibitor development may provide an attractive approach to prevent inhibitor formation before amplification of the FVIII immune response occurs. As the initial steps in FVIII inhibitor development remain incompletely understood, we sought to define early regulators of FVIII inhibitor formation. Our results demonstrate that FVIII localizes in the marginal sinus of the spleen of FVIII-deficient mice shortly after injection, with significant colocalization with marginal zone (MZ) B cells. FVIII not only colocalizes with MZ B cells, but specific removal of MZ B cells also completely prevented inhibitor development following FVIII infusion. Subsequent rechallenge with FVIII following MZ B-cell reconstitution resulted in a primary antibody response, demonstrating that MZ B-cell depletion did not result in FVIII tolerance. Although recipient exposure to the viral-like adjuvant polyinosinic:polycytidylic acid enhanced anti-FVIII antibody formation, MZ B-cell depletion continued to display similar effectiveness in preventing inhibitor formation following FVIII infusion in this inflammatory setting. These data strongly suggest that MZ B cells play a critical role in initiating FVIII inhibitor formation and suggest a potential strategy to prevent anti-FVIII alloantibody formation in patients with hemophilia A.

The endothelial cell receptor stabilin-2 regulates VWF-FVIII complex half-life and immunogenicity

“…As LSECs express stabilin-2, MHC II, and costimulatory molecules, although at relatively low levels, there is a potential that they may function as APCs capable of presenting VWF-FVIII peptides to cognate CD4 + T cells (57,58). However, it is more likely that stabilin-2 expressed on the splenic sinusoidal endothelium acts as a key mediator in the directed shuttling of FVIII antigen in a VWF-dependent manner through marginal zone macrophage and marginal B cell compartments of the spleen (11,59,60). Furthermore, engagement of stabilin-2 initiates signaling through extracellular signal-regulated kinases 1 and 2 (ERK1/2), and can induce NF-κB activation of proinflammatory gene expression that can, in turn, enhance the likelihood of an immune response (61).…”

Anemia induces gut inflammation and injury in an animal model of preterm infants

“…Intestines were harvested after 1 hour. Tissue sections were prepared as described previously . 5 μm tissue sections were stained with anti‐pimonidazole (clone 4.3.11.3) (1:500, overnight, 4°C), followed by goat anti‐mouse IgG Alexa‐555 (ThermoFisher) (1:500, 1 hour, room temperature).…”

The national blueprint for future basic and translational research to understand factor VIII immunogenicity: NHLBI State of the Science Workshop on factor VIII inhibitors

“…been implicated in initial FVIII uptake in lymphoid organs. 7,8 How these innate factors and cell types (including innate immune and antigen presenting cells [APCs]) interact during the transition from initial innate immune signalling to the adaptive immune response remains to be defined.…”

“…For example, bacterial lipopolysaccharide (LPS) functions as an adjuvant and enhances FVIII inhibitor formation in haemophilic mice. Certain types of macrophages and marginal zone B cells have also been implicated in initial FVIII uptake in lymphoid organs . How these innate factors and cell types (including innate immune and antigen presenting cells [APCs]) interact during the transition from initial innate immune signalling to the adaptive immune response remains to be defined.…”