Eosinophils are not essential for maintenance of murine plasma cells in the bone marrow

Eosinophils were reported to serve as an essential component of the plasma cell niche within the bone marrow. As the potential contribution of eosinophils to humoral immunity has remained incompletely understood, we aimed to further characterize their role during antibody responses and to additionally investigate their role in autoimmune disease. Contrary to our expectations and the currently prevailing paradigm, we found that eosinophils are fully dispensable for the survival of murine bone marrow plasma cells and accordingly do not contribute to antibody production and autoantibody‐mediated disease. Littermate wild type and eosinophil‐deficient ΔdblGATA‐1 animals showed similar numbers and frequencies of plasma cells and did not differ in steady state levels of immunoglobulins or their ability to raise antigen‐specific antibody responses. Eosinophils were likewise dispensable for autoantibody production or autoantibody‐induced disease in a mouse model of systemic lupus erythematosus. Our findings thus argue against a role of eosinophils during the maintenance of the plasma cell pool and challenge the hitherto postulated concept of an eosinophil‐sustained bone marrow niche. Eosinophils are nonessential for the production of plasma cell survival factors and for the maintenance of the plasma cell survival niche. Other cell types produce these survival factors and compensate for a lack of eosinophils in this context by enabling the survival of long lived plasma cells in the bone marrow in the absence of eosinophils.