||The role of Ly-6A.2 in B cell development and function is not known. The goal of this research is to elucidate this role by using mice in which Ly-6A.2 has been knocked out and comparing B cell function and development to wildtype animals. In these animals, it was found that while conventional B cells developed normally, there were deficiencies in B-1a and B-1b cells in knockout mice. B-1 cells are a recently described B cell subset that populate the peritoneal cavity and are involved in early defense against pathogens. Functionally, enzyme-linked immunosorbance assays (ELISA) and cytometric bead array (CBA) indicated that knockout animals have significantly higher levels of immunoglobulin A (IgA) both prior to and following exposure to chicken ovalbumin (OVA). IgM, IgG1, and IgG2a anti-OVA antibodies are comparable in wildtype and knockout mice. Together, these data suggest a role for Ly-6A.2 in B cell development and function and demonstrate the need for further studies in this area of research.