The coordination of macrophage polarization is essential for the robust regenerative potential of skeletal muscle. Repair begins with an inflammatory monocyte/pro-inflammatory macrophage (M1)-mediated phase followed by polarization to a pro-regenerative (M2) phenotype. Recently, regulatory T cells (Tregs) were described as necessary for this M1 to M2 transition. Here, we report that chronic infection with the protozoan parasite Toxoplasma gondii causes a non-resolving Th1 myositis with prolonged tissue damage associated with persistent M1 accumulation. Surprisingly, Treg ablation during chronic infection rescues macrophage homeostasis and skeletal muscle fiber regeneration showing that Tregs can directly contribute to muscle damage. This study provides evidence that the tissue environment established by the parasite could lead to a paradoxical pathogenic role for Tregs. As such, these findings should be considered when tailoring therapies directed at Tregs in inflammatory settings.

PurposeDendritic cell (DC) vaccines have recently emerged as an innovative therapeutic option for glioblastoma patients. To identify novel surrogates of anti-tumor immune responsiveness, we studied the dynamic expression of activation and inhibitory markers on peripheral blood lymphocyte (PBL) subsets in glioblastoma patients treated with DC vaccination at UCLA.Experimental DesignPre-treatment and post-treatment PBL from 24 patients enrolled in two Phase I clinical trials of dendritic cell immunotherapy were stained and analyzed using flow cytometry. A univariate Cox proportional hazards model was utilized to investigate the association between continuous immune monitoring variables and survival. Finally, the immune monitoring variables were dichotomized and a recursive partitioning survival tree was built to obtain cut-off values predictive of survival.ResultsThe change in regulatory T cell (CD3+CD4+CD25+CD127low) frequency in PBL was significantly associated with survival (p = 0.0228; hazard ratio = 3.623) after DC vaccination. Furthermore, the dynamic expression of the negative co-stimulatory molecule, CTLA-4, was also significantly associated with survival on CD3+CD4+ T cells (p = 0.0191; hazard ratio = 2.840) and CD3+CD8+ T cells (p = 0.0273; hazard ratio = 2.690), while that of activation markers (CD25, CD69) was not. Finally, a recursive partitioning tree algorithm was utilized to dichotomize the post/pre fold change immune monitoring variables. The resultant cut-off values from these immune monitoring variables could effectively segregate these patients into groups with significantly different overall survival curves.ConclusionsOur results suggest that monitoring the change in regulatory T cell frequencies and dynamic expression of the negative co-stimulatory molecules on peripheral blood T cells, before and after DC vaccination, may predict survival. The cut-off point generated from these data can be utilized in future prospective immunotherapy trials to further evaluate its predictive validity.

A common feature shared by systemic fungal pathogens of environmental origin, such as Cryptococcus neoformans, is their ability to adapt to mammalian core body temperature. In C. neoformans, this adaptation is accompanied by Ccr4-mediated decay of ribosomal protein mRNAs. Here we use the related, but thermo-intolerant species Cryptococcus amylolentus to demonstrate that this response contributes to host-temperature adaptation and pathogenicity of cryptococci. In a C. neoformans ccr4Δ mutant, stabilized ribosomal protein mRNAs are retained in the translating pool, and stress-induced transcriptomic changes are reduced in comparison with the wild type strain, likely due to ineffective translation of transcription factors. In addition, the mutant displays increased exposure of cell wall glucans, and recognition by Dectin-1 results in increased phagocytosis by lung macrophages, linking mRNA decay to adaptation and immune evasion.

The robust regenerative potential of skeletal muscle is imperative for the maintenance of tissue function across a host of potential insults including exercise, infection, and trauma. The highly coordinated action of multiple immune populations, especially macrophages, plays an indispensable role in guiding this reparative program. However, it remains unclear how skeletal muscle repair proceeds in a chronically inflamed setting, such as infection, where an active immune response is already engaged. To address this question, we used a cardiotoxin injury model to challenge the reparative potential of chronically infected muscle. Compared with regenerating naive skeletal muscle, infected skeletal muscle exhibited multiple indicators of delayed muscle repair including a divergent morphologic response to injury and dysregulated expression of myogenic regulatory factors. Further, using both flow cytometric and single-cell RNA sequencing approaches, we show that reduced macrophage heterogeneity due to delayed emergence of restorative subsets underlies dysfunctional tissue repair during chronic infection. Our findings highlight how the preexisting inflammatory environment within tissue alters reparative immunity and ultimately the quality of tissue regeneration.

Maintenance of tissue integrity in skeletal muscle requires the immunomodulatory and regenerative functions of muscle-resident regulatory T cells (Tregs). Chronic skeletal muscle infections, such as with Toxoplasma gondii disrupt normal immuno-regulatory networks and lead to pathogenic changes in Treg function. Specifically, Tregs during chronic T. gondii infection reinforce an inflammatory macrophage bias that exacerbates injury in skeletal muscle. In this study, we investigated whether the aberrations in skeletal muscle Treg function during chronic infection could be overcome by treatment with Treg-related factors associated with enhanced muscle regeneration during sterile injury. We show treatment of chronically infected mice with the Treg promoting therapies, interleukin-2 complexed with anti-IL-2 antibody or interleukin-33 (IL-33), did not restore macrophage dynamics or muscle function, respectively, in vivo. However supplementation of known Treg-derived factors, interleukin-10 (IL-10) and amphiregulin (Areg) improved muscle function and skewed macrophages toward a restorative phenotype in the presence of chronic infection. These shifts in macrophage phenotype are coupled with enhanced physiologic parameters of regeneration. Together, these data suggest that while Treg-mediated immuno-regulation is compromised during chronic skeletal muscle infection, supplementation of canonical Treg-derived factors such as IL-10 and Areg can restore immunologic balance and enhance muscle repair.