Trafficking and Repopulation of Donor B Cells in a Minor-Mismatched Mouse Lung Transplant Model

Abstract

Previous work has shown that B cells are necessary for the development of chronic allograft fibrosis after ischemia-reperfusion injury (IRI) in a C57BL/10 (B10, H-2b)-to-C57BL/6 (B6, H-2b) minor alloantigen-mismatched mouse orthotopic lung transplant model. It remains unknown whether donor-derived B cells play a specific role in this phenomenon and how long they survive in the recipient. We hypothesized that donor B cells are short-lived and thus play a minimal role in the recipient. We conducted B10 to B6 lung transplants without IRI using congenic donors and recipients. Donors were treated 2 days before transplantation with an anti-CD20 antibody or its isotype control. We used flow cytometry to track B cell populations in the donor and recipient before and up to 28 days after transplantation. Anti-CD20 effectively eliminated >85% of B cells from donor lungs prior to transplantation (Fig 1A). We observed low frequencies of donor (CD45.2+) B cells in the recipient (CD45.1+) peripheral blood after transplantation (Fig 1B). Despite profound B cell depletion in donor lungs, donor-derived B cells were unexpectedly still present in the allograft (median 3.5%, range 2.3-10%), thoracic lymph nodes (median 0.5%, range 0.2-1.5%) and spleen (median 1.2%, range 0.7-1.7%) at day 28 irrespective of anti-CD20 treatment (Fig 1C). B and plasma cells constituted >80% of donor-derived leukocytes observed in the recipient spleen at day 28. As expected, given the lack of IRI, allograft histology showed minimal rejection and fibrosis with no effect of anti-CD20 observed (Fig 1D). Donor-derived B cells repopulated in the recipients to a similar extent in both groups on day 28. These findings suggest donor-derived B cells may play important functional roles after transplantation. An examination of the role of donor- and recipient-derived B cells in IRI-augmented lung allograft fibrosis is now underway.