Activation and trafficking of peritoneal B1a B-cells in response to amphibole asbestos

B1a B-cells are concentrated in peritoneal and pleural cavities, are producers of 'natural auto-antibodies', and have been implicated in autoimmune responses. Their numbers are increased in humans and mice with systemic autoimmune diseases, but their role in the immune pathology is not known. Asbestos causes pulmonary, pleural, and peritoneal pathologies by accessing these tissues after inhalation. Amphibole asbestos has been shown to elicit immune dysfunction, including chronic inflammation, fibrosis, and autoantibody production. This study tested the hypothesis that asbestos affects immune dysfunction by activating B1a B-cells to traffic to secondary lymphatic tissue. C57Bl/6 mice were exposed to amphibole asbestos (Libby 6-Mix) either endotracheally or intraperitoneally, and the B1a B-cells in pleural or peritoneal compartments were tested by multi-parameter flow cytometry. Adoptive transfer of peritoneal lymphocytes from CD45.1 transgenic to wild-type mice was used to track the migration. The percentage and numbers of B1a B-cells in pleural and peritoneal cavities decreased 3-6 days following exposure. During that time, asbestos exposure led to a decrease in cells expressing alpha-4 (α4) integrin and MHC II antigen. Peritoneal cells treated in vitro showed decreased α4 integrin with no change in CD5, IgM, or MHC II antigen. Therefore, B1a cells (IgM(+), CD5(+), MHC II(+)) traffic from the peritoneal cavity following loss of α4 integrin expression. Following adoptive transfer into the peritoneum of asbestos-exposed mice, CD45.1(+) B1a cells were detected in the spleen and mesenteric lymph nodes after 3 days, peaking at 6 days. Interestingly, the percentage of splenic suppressor B-cells (IgM(+), CD5(+), CD11b(+), CD1d(+)) decreased following amphibole exposure, demonstrating that the B1a cells did not contribute to an increased pool of suppressive B-cells. These results show that B1a B-cells respond to asbestos exposure by trafficking to secondary lymphatic tissue where they may affect ultimate immune dysfunction.