SiiE prevents an efficient humoral immune memory by interfering with IgG plasma cell persistence in the bone marrow.

Serum IgG, which is mainly generated from IgG-secreting plasma cells in the bone marrow (BM), protects our body against various pathogens. We show here that the protein SiiE of is both required and sufficient to prevent an efficient humoral immune memory against the pathogen by selectively reducing the number of IgG-secreting plasma cells in the BM. Attenuated SiiE-deficient induces high and lasting titers of specific and protective -specific IgG and qualifies as an efficient vaccine against A SiiE-derived peptide with homology to laminin β1 is sufficient to ablate IgG-secreting plasma cells from the BM, identifying laminin β1 as a component of niches for IgG-secreting plasma cells in the BM, and furthermore, qualifies it as a unique therapeutic option to selectively ablate IgG-secreting plasma cells in autoimmune diseases and multiple myeloma.