Loss of intrasplenic 33D1+DC migration impairs alloimmune responses against RBC transfusion

Abstract Although the migration of tissue DCs from periphery to draining LNs is the crucial step for the induction of T cell responses, it is not clear whether the same holds true within the spleen. Here we use red blood cell (RBC) transfusion model to specifically study intrasplenic DC migration in the induction of alloantibodies to blood group antigens present on the donor RBCs. We observed that mice deficient in DOCK8 (dedicator of cytokinesis 8), a guanine nucleotide exchange factor that regulates the activity of Rho GTPase family members, fail to produce alloantibodies following transfusion. Two major splenic conventional DC subsets, the Batf3-dependent CD8+ XCR1+ subset and the IRF-4-dependent CD11b+33D1+ subset, prime CD4+ and CD8+ T cells, respectively. Our data demonstrate that only bridging channel 33D1+ DCs migrate to the T cell zone to initiate CD4+ T cell responses during RBC transfusion. Using in vivo antibody labeling method, we are able to differentiate marginal zone/red pulp dendritic cells from T cell zone/white pulp dendritic cells. In vivo labeling reveals that the failure of generating alloantibodies to RBCs in DOCK8 deficient mice is due to impaired 33D1+ DC migration. Interestingly, although the XCR1+ DCs in DOCK8 deficient mice migrated normally, they played no role in alloimmune responses. Taken together, our data demonstrate that subset specific migration of DCs within spleen is critical for initiation of CD4 T cell response and generation of alloantibodies. As equivalent populations of DC subsets exist in humans, our work suggests that blocking certain DC subset migration therapeutically during RBC transfusion could potentially prevent the harmful sensitization that occurs in patients who require lifelong RBC support.