Defining the Role of Marginal Zone B Cells in RBC Alloimmunization.

Red blood cell (RBC) transfusions are critical for treating a range of hematologic and surgical conditions but carry the risk of alloimmunization, particularly in chronically transfused individuals such as those with sickle cell disease. The development of alloantibodies complicates subsequent transfusions, increases the likelihood of hemolytic reactions, and can undermine curative interventions like bone marrow transplantation. Although current preventive strategies, including extended antigen matching, have reduced alloimmunization rates, they are not universally effective. Recent findings using the HOD mouse model, which expresses hen egg lysozyme, ovalbumin, and the human Duffy antigen, highlight a pivotal role for marginal zone (MZ) B cells in initiating alloantibody responses. Depletion of MZ B cells markedly impairs both IgM and IgG production, suggesting an alternative immune activation pathway independent of conventional germinal center responses driven by T follicular helper and follicular B cells. Additionally, transfused RBC immunogenicity appears to be modulated by antigen-intrinsic factors such as storage duration, emphasizing the influence of antigen-specific properties on immune outcomes. These insights reveal a complex interplay between cellular and antigenic determinants in shaping alloimmune responses. Advanced tools like flow cytometry and immunohistochemistry have proven indispensable in dissecting these mechanisms and hold promise for guiding the development of more effective strategies to prevent RBC alloimmunization.