PD-L1 Prevents the Development of Autoimmune Heart Disease in Graft-versus-Host Disease.

Effector memory T cells (TEM) are less capable of inducing graft-versus-host disease (GVHD) compared with naive T cells (TN). Previously, in the TS1 TCR transgenic model of GVHD, wherein TS1 CD4 cells specific for a model minor histocompatibility Ag (miHA) induce GVHD in miHA-positive recipients, we found that cell-intrinsic properties of TS1 TEM reduced their GVHD potency relative to TS1 TN Posttransplant, TS1 TEM progeny expressed higher levels of PD-1 than did TS1 TN progeny, leading us to test the hypothesis that TEM induce less GVHD because of increased sensitivity to PD-ligands. In this study, we tested this hypothesis and found that indeed TS1 TEM induced more severe skin and liver GVHD in the absence of PD-ligands. However, lack of PD-ligands did not result in early weight loss and colon GVHD comparable to that induced by TS1 TN, indicating that additional pathways restrain alloreactive TEM TS1 TN also caused more severe GVHD without PD-ligands. The absence of PD-ligands on donor bone marrow was sufficient to augment GVHD caused by either TEM or TN, indicating that donor PD-ligand-expressing APCs critically regulate GVHD. In the absence of PD-ligands, both TS1 TEM and TN induced late-onset myocarditis. Surprisingly, this was an autoimmune manifestation, because its development required non-TS1 polyclonal CD8+ T cells. Myocarditis development also required donor bone marrow to be PD-ligand deficient, demonstrating the importance of donor APC regulatory function. In summary, PD-ligands suppress both miHA-directed GVHD and the development of alloimmunity-induced autoimmunity after allogeneic hematopoietic transplantation.

A repertoire-independent and cell-intrinsic defect in murine GVHD induction by effector memory T cells.

Effector memory T cells (T(EM)) do not cause graft-versus-host disease (GVHD), though why this is has not been elucidated. To compare the fates of alloreactive naive (T(N)) or memory (T(M)) T cells, we developed a model of GVHD in which donor T cells express a transgene-encoded TCR specific for an antigenic peptide that is ubiquitously expressed in the recipient. Small numbers of naive TCR transgenic (Tg) T cells induced a robust syndrome of GVHD in transplanted recipients. We then used an established method to convert TCR Tg cells to T(M) and tested these for GVHD induction. This allowed us to control for the potentially different frequencies of alloreactive T cells among T(N) and T(M), and to track fates of alloreactive T cells after transplantation. T(EM) caused minimal, transient GVHD whereas central memory T cells (T(CM)) caused potent GVHD. Surprisingly, T(EM) were not inert: they, engrafted, homed to target tissues, and proliferated extensively, but they produced less IFN-γ and their expansion in target tissues was limited at later time points, and local proliferation was reduced. Thus, cell-intrinsic properties independent of repertoire explain the impairment of T(EM), which can initiate but cannot sustain expansion and tissue damage.

NFAM1 Promotes Pro-Inflammatory Cytokine Production in Mouse and Human Monocytes.

NFAT activating protein with ITAM motif 1 (NFAM1) is an ITAM bearing-transmembrane receptor that has been reported to play a role in B cell signaling and development. We performed expression analysis of NFAM1 using publicly available gene expression data sets and found that NFAM1 expression is significantly induced in intestinal biopsies from Crohn's disease (CD) and ulcerative colitis (UC) patients. At the cellular level, we further observed high expression of NFAM1 in monocytes and neutrophils, and low expression in B and T cells. To explore the role of NFAM1 in multiple immune cells and its potential role in IBD, we generated NFAM1-/- mice. In contrast with previous reports using NFAM1-transgenic mice, NFAM1-/- mice have no obvious defects in immune cell development, or B cell responses. Interestingly, NFAM1-/- monocytes produce reduced levels of TNF-α in response to activation by multiple IBD-relevant stimuli, including CD40L, TLR ligands and MDP. Additional cytokines and chemokines such as IL-6, IL-12, CCL3 and CCL4 are also reduced in CD40L stimulated NFAM1-/- monocytes. Collectively, these findings indicate that NFAM1 promotes monocyte activation, thereby amplifying the response to diverse stimuli. Similarly, we observed that deletion of NFAM1 in human monocytes reduces expression of CD40L-induced CCL4. Lastly, to assess the role of NFAM1 in IBD, we compared development of anti-CD40 induced colitis in NFAM1+/+ and NFAM1-/- mice. We found that although NFAM1 deletion had no impact on development of gut pathology, we did observe a decrease in serum TNF-α, confirming that NFAM1 promotes pro-inflammatory cytokine production in vivo. Taken together, we conclude that NFAM1 functions to amplify cytokine production and should be further evaluated as a therapeutic target for treatment of autoimmune disease.

RNA sequencing of microglia and monocyte-derived macrophages from mice with experimental autoimmune encephalomyelitis illustrates a changing phenotype with disease course.

The role of microglia and monocyte-derived macrophages in experimental autoimmune encephalomyelitis pathogenesis has been controversial. To gain insight into their respective roles, we developed a method for differentiating between microglia and monocyte-derived macrophages in the CNS by flow cytometry utilizing anti-CD44 antibodies. We used this system to monitor changes in cell number, activation status, and gene expression by RNA sequencing over the course of disease. This in vivo characterization and RNA-Seq dataset improves our understanding of macrophage biology in the brain under inflammatory conditions and may lead to strategies to identify therapies for neuroinflammatory diseases.