β1 Integrin Is Not Essential for Hematopoiesis but Is Necessary for the T Cell-Dependent IgM Antibody Response

Several experimental evidences suggested that β1 integrin-mediated adhesion of hematopoietic stem cells (HSC) is important for their function in the bone marrow (BM). Using induced deletion of the β1 integrin gene restricted to the hematopoietic system, we show that β1 integrin is not essential for HSC retention in the BM, hematopoiesis, and trafficking of lymphocytes. However, immunization with a T cell-dependent antigen resulted in virtually no IgM production and an increased secretion of IgG in mutant mice, while the response to a T cell-independent type 2 antigen showed decreases in both IgM and IgG. These data suggest that β1 integrins are necessary for the primary IgM antibody response.