Rapamycin prevents bronchiolitis obliterans through increasing infiltration of regulatory B cells in a murine tracheal transplantation model

Abstract

Objective B lymphocytes are generally considered to be activators of the immune response, However recent findings have shown that a subtype of B-lymphocytes, regulatory B lymphocytes (Bregs) play a role in attenuating the immune response. Bronchiolitis obliterans (BO) remains the major limitation to modern day lung transplantation. Bregs role in BO has not been elucidated. We hypothesized that Bregs play a role in the attenuation of BO. Methods A standard heterotopic tracheal transplant model (HTT) model we performed. Tracheas from Balb/c were transplanted into C57BL/6 recipients. Rapamycin treatment and DMSO control groups each treated for the first 14 days after the transplant. Tracheas were collected on Days 7, 14, and 28 post-transplantation. Luminal obliteration was evaluated by HE staining and picrosirius red staining. Immune cell infiltration and characteristics, secretion of IL-10 and TGF-β1 were accessed by immunohistochemistry. Cytokines and TGF-β1 were measured using luminex assay. Results The results revealed that intraperitoneal injection of rapamycin for 14 days after tracheal transplantation significantly reduced luminal obliteration on days 28 when compared with DMSO control group (97.78% ±3.63% Vs 3.02% ±2.14%, P<0.001). Rapamycin treatment markedly induced Breg (B220+IgM+IgG- IL-10+TGF- β1+) cells when compared with DMSO controls. Rapamycin treatment inhibited IL-1β, -6, -13 and -17 at day 7 and 14. Furthermore, rapamycin also greatly increased IL-10 and TGF-β1 production in B cells and Treg infiltration on day 28. Conclusions mTOR inhibition decreases BO development via inhibition of pro-inflammatory cytokines and increasing Breg cell infiltration, which subsequently produce anti-inflammatory cytokines and upregulate Treg cells.

Importance of B cells to development of regulatory T cells and prolongation of tissue allograft survival in recipients receiving autologous bone marrow transplantation

“…As mentioned previously, in patients receiving autologous HSCT for systemic sclerosis, increased Breg cells were seen at 6 and 12 months post transplant with no differences observed in levels of Treg cell . All transplanted mice in our studies receive rapamycin post transplantation of both skin and marrow, and this drug can regulate intra‐graft infiltration of Breg cells in vivo in association with augmented graft survival . To date, Breg cell subsets with various phenotypes (such as B10 cells and marginal zone B cells) have been defined but there is no consensus as to which surface markers are definitive .…”

“…Breg cells can contribute to the induction of Treg cells and attenuation of immune responses including those contributing to graft rejection . Based on the loss of all suppression seen in vitro following treatment of splenocytes from grafted mice with either anti‐Thy1.2, or combined anti‐CD45.1 and anti‐CD45.2, we concluded that the regulation seen at 60 days post grafting was attributable to Treg cells and not to other populations (including Breg cells).…”

“…Regulatory B cells, a heterogeneous group of B lymphocytes with immunosuppressive functions, have attracted a great deal of interest in transplant models . TGF‐ β ‐producing Breg cells promote graft survival by increasing the number of Treg cells, but Breg cells can also mediate tolerance in other ways.…”

“…Regulatory B cells, a heterogeneous group of B lymphocytes with immunosuppressive functions, 5,6 have attracted a great deal of interest in transplant models. 8,10,11,13 TGFb-producing Breg cells promote graft survival by increasing the number of Treg cells, 8 but Breg cells can also mediate tolerance in other ways. In a cardiac allograft model, long-term graft survival was achieved by overexpression of the immunosuppressive molecule FGL2.…”

Influence of the Novel ATP-Competitive Dual mTORC1/2 Inhibitor AZD2014 on Immune Cell Populations and Heart Allograft Rejection

“…Others have shown that RAPA increases graft-infiltrating IL-10 + transforming growth factor β + Breg in a mouse tracheal transplant model. 50 Thus, based on these preclinical data, one might expect RAPA to exert suppressive effects on human pathogenic complement-fixing IgG1 and IgG3 DSA generation posttransplant. 51 Paradoxically however, compared to standard calcineurin inhibitor-based immunosuppression, several retrospective analyses have documented a higher incidence of de novo DSA in kidney transplant patients treated with mTOR inhibitors.…”