<i>Pseudomonas aeruginosa</i> infection induces intragraft lymphocytotoxicity that triggers lung transplant antibody-mediated rejection

How pathogens inhibit transplant tolerance remains unclear. Here, we found that <i>Pseudomonas aeruginosa</i> infection, but not other common bacterial respiratory infections, increases antibody-mediated rejection (AMR) risk in recipients of lung transplants. To explore this relationship, we performed orthotopic lung transplants in mice, infected recipients with <i>P. aeruginosa</i>, and observed for the development of AMR. Intravital two-photon microscopy showed that <i>P. aeruginosa</i> rapidly invaded bronchial-associated lymphoid tissues, which resulted in acute lymphocytotoxicity, including the death of forkhead box P3 (Foxp3)⁺CD4⁺ T cells that are required to suppress AMR. <i>P. aeruginosa</i>-mediated AMR required expression of the type III secretion system (T3SS), which injects exotoxins into the cell cytoplasm. Through a combination of mutagenesis and epitope tagging experiments, we revealed that T3SS exotoxin T ADP ribosyl-transferase activity was sufficient for graft-resident Foxp3⁺CD4⁺ T cell apoptosis, leading to myeloid differentiation primary response 88 (Myd88)-dependent generation of T-box expressed in T cells (T-bet)- and C-X-C motif chemokine receptor 3 (CXCR3)-positive germinal center and memory B cells with high donor antigen avidity. We also found that T-bet⁺ and CXCR3⁺ B cells were elevated in biopsies from recipients of lung transplants who were diagnosed with AMR. In mice, CXCR3 deficiency restricted to B cells or CXCR3 blockade prevented AMR despite <i>P. aeruginosa</i> infection. Our work has identified a previously unrecognized role of bacterial virulence in lung allograft rejection and suggests potential strategies to prevent AMR for those at high risk of <i>P. aeruginosa</i> infection after transplant.