Tolerization of recent thymic emigrants is required to prevent RBC-specific autoimmunity.

Autoimmune hemolytic anemia (AIHA) leads to accelerated destruction of autologous red blood cells (RBCs) by autoantibodies. AIHA is a severe and sometimes fatal disease. While there are several therapeutic strategies available, there are currently no licensed treatments for AIHA and few therapeutics result in treatment-free durable remission. The etiology of primary AIHA is unknown; however, secondary AIHA occurs concurrently with lymphoproliferative disorders and infections. Additionally, AIHA is the second most common manifestation of primary immunodeficiency disorders and has been described as a side effect of checkpoint inhibitor therapy. Given the severity of AIHA and the lack of treatment options, understanding the initiation of autoimmunity is imperative. Herein, we utilized a well-described model of RBC biology to dissect how RBC-specific autoreactive T cells become educated against RBC autoantigens. We show that, unlike most autoantigens, T cells do not encounter RBC autoantigens in the thymus. Instead, when they leave the thymus as recent thymic emigrants (RTEs), they retain the ability to positively respond to RBC autoantigens; only after several weeks in circulation do RTEs become nonresponsive. Together, these data suggest that any disruption in this process would lead to breakdown of tolerance and initiation of autoimmunity. Thus, RTEs and this developmental process are potential targets to prevent and treat AIHA.

Alloimmunogenicity of an isolated MHC allele is affected by the context of MHC mismatch in a murine model.

BACKGROUND: Humoral alloimmunization to human leukocyte antigen (HLA) can represent a barrier to solid-organ transplantation, can lead to a refractory state in patients requiring platelet transfusion, and can also contribute to transfusion-related acute lung injury (TRALI). While exposure to HLA-mismatched cells/tissues are generally required for HLA alloimmunization, the effect of the extent of major histocompatibility complex (MHC) mismatch between donor and recipient is poorly understood. STUDY DESIGN AND METHODS: A novel mouse was generated that allows the expression of a single MHC Class I alloantigen, Kd . Alloimmune responses to Kd were studied in C57BL/6 mice transfused with splenocytes from different donor mice, allowing the analysis of responses to Kd as an isolated alloantigen, or in the context of additional mismatched MHC molecules. Advanced tools were utilized to study responses to Kd , including T-cell receptor transgenic mice that recognize the immunodominant Kd peptide presented by C57BL/6 mice to CD4+ T cells. RESULTS: A single MHC Class I alloantigen mismatch is less immunogenic than when the same alloantigen is encountered in the context of additional mismatched MHC alloantigens. This difference is due, at least in part, to induction of CD4+ helper T cells, as the effect is overcome by increasing either mature CD4+ T-cell help through immunization or by increasing the precursor frequency of naïve CD4+ T cells by adoptive transfer from T-cell receptor transgenic donors. CONCLUSION: These findings indicate that the immunogenicity of a single alloantigen can be affected by the context in which it is encountered, demonstrating the potential for cooperative effects between different mismatched MHC alloantigens.

γδ T cells are essential effectors of type 1 diabetes in the nonobese diabetic mouse model.

γδ T cells, a lineage of innate-like lymphocytes, are distinguished from conventional αß T cells in their Ag recognition, cell activation requirements, and effector functions. γδ T cells have been implicated in the pathology of several human autoimmune and inflammatory diseases and their corresponding mouse models, but their specific roles in these diseases have not been elucidated. We report that γδ TCR(+) cells, including both the CD27(-)CD44(hi) and CD27(+)CD44(lo) subsets, infiltrate islets of prediabetic NOD mice. Moreover, NOD CD27(-)CD44(hi) and CD27(+)CD44(lo) γδ T cells were preprogrammed to secrete IL-17, or IFN-γ upon activation. Adoptive transfer of type 1 diabetes (T1D) to T and B lymphocyte-deficient NOD recipients was greatly potentiated when γδ T cells, and specifically the CD27(-) γδ T cell subset, were included compared with transfer of αß T cells alone. Ab-mediated blockade of IL-17 prevented T1D transfer in this setting. Moreover, introgression of genetic Tcrd deficiency onto the NOD background provided robust T1D protection, supporting a nonredundant, pathogenic role of γδ T cells in this model. The potent contributions of CD27(-) γδ T cells and IL-17 to islet inflammation and diabetes reported in this study suggest that these mechanisms may also underlie human T1D.

CD44 interacts directly with Lck in a zinc-dependent manner.

CD44 is a widely expressed cell adhesion molecule with functional similarities to the selectin and integrin adhesion molecules. CD44 has a lectin domain that binds hyaluronan, a component of the extracellular matrix. Interactions between CD44 and hyaluronan promote lymphocyte rolling under flow and cell-cell and cell-matrix adhesion. Attachment of lymphocytes to immobilized CD44 antibodies induces cell adhesion and spreading, which is dependent on Src family kinase activity. Both Lck and Fyn associate with CD44 in T cells. CD4 and CD8 associate with Lck via a zinc-dependent interaction that is inhibited by the divalent metal cation chelator, 1,10-phenanthroline. Here we show that both CD4 and CD44-mediated T cell spreading is abolished in the presence of 1,10-phenanthroline and their association with Lck is significantly reduced. In contrast, the co-immunoprecipitation of Fyn by CD44 was unaffected. The cytoplasmic domain of CD44 was required for divalent cation-dependent association of Lck, but not for its association with Fyn. Mutational analysis of CD44 revealed that cysteine residues were not essential for the interaction nor were the carboxy-terminal 41 amino acids. Progressive deletion of the remaining 31 amino acids of the CD44 cytoplasmic domain revealed the importance of this membrane proximal region for its association with Lck. Using purified recombinant proteins, we demonstrated a direct, zinc-inducible interaction between the cytoplasmic domain of CD44 and Lck but not Fyn. The zinc-inducible interaction required the first 13 amino acids of the cytoplasmic domain of CD44 and the non-catalytic regions of Lck. Taken together, we conclude that CD44 directly associates with Lck in a zinc-inducible manner and this is important for the transmission of CD44-mediated signaling events leading to T cell spreading.