Michelle L. McCully

Toll-like receptor 2 ligands on the staphylococcal cell wall downregulate superantigen-induced T cell activation and prevent toxic shock syndrome

Staphylococcal superantigens are pyrogenic exotoxins that cause massive T cell activation leading to toxic shock syndrome and death. Despite the strong adaptive immune response induced by these toxins, infections by superantigen-producing staphylococci are very common clinical events. We hypothesized that this may be partly a result of staphylococcal strains having developed strategies that downregulate the T cell response to these toxins. Here we show that the human interleukin-2 response to staphylococcal superantigens is inhibited by the simultaneous presence of bacteria. Such a downregulatory effect is the result of peptidoglycan-embedded molecules binding to Toll-like receptor 2 and inducing interleukin-10 production and apoptosis of antigen-presenting cells. We corroborated these findings in vivo by showing substantial prevention of mortality after simultaneous administration of staphylococcal enterotoxin B with either heat-killed staphylococci or Staphylococcus aureus peptidoglycan in mouse models of superantigen-induced toxic shock syndrome.

Characterization of human peritoneal dendritic cell precursors and their involvement in peritonitis

Scattered evidence suggests that the human peritoneal cavity contains cells of the dendritic cell (DC) lineage but their characterization is missing. Here, we report that the peritoneal cavity of normal subjects and of stable patients on peritoneal dialysis (PD) contains a population of CD14+ cells that can differentiate into DCs or macrophages. Within this pool, we characterized a CD14+CD4+ cell subset (2·2% of the peritoneal cells) fulfilling the definition of myeloid DC precursors or pre‐DC1 cells. These cells expressed high levels of HLA‐DR, CD13, CD33, and CD86, and low levels of CD40, CD80, CD83, CD123, CD209, TLR‐2 and TLR‐4. These cells retained CD14 expression until late stages of differentiation, despite concomitant up‐regulation of DC‐SIGN (CD209), CD1a, CD80 and CD40. Peritoneal pre‐DC1 cells had endocytic capacity that was down‐regulated upon LPS/IFN‐γ stimulation, were more potent allo‐stimulators than peritoneal CD14+CD4–/lo cells and monocyte‐derived macrophages, and induced Th1 cytokine responses. More importantly, the number of peritoneal pre‐DC1 cells increased during PD‐associated peritonitis, with a different profile for Gram positive and Gram negative peritonitis, suggesting that these cells participate in the induction of peritoneal adaptive immune responses, and may be responsible for the bias towards Th1 responses during peritonitis.

RIP2 Is Required for NOD Signaling But Not for Th1 Cell Differentiation and Cellular Allograft Rejection

Two previous reports that receptor‐interacting protein (RIP)‐2 knockout (RIP2–/–) mice had defective nuclear factor‐kappa B (NF‐κB) signaling and T helper (Th)1 immune responses had led us to believe that this putative serine‐threonine kinase might be a possible target for transplant immunosuppression. Thus, we tested whether RIP2–/– mice were able to reject vascularized allografts. Surprisingly, we found that T cells from RIP2–/– mice proliferated and produced interferon (IFN)‐γ after allostimulation in vitro. Moreover, naïve RIP2–/– CD4+ T cells differentiated normally into Th1 or Th2 cells under appropriate cytokine microenvironments. Consistent with these findings, no difference in allograft survival was observed between wild‐type and RIP2–/– recipient mice, and rejection had similar pathology and cytokine profiles in both types of recipients. RIP2 deficiency was associated with defective NOD signaling, but this did not affect T‐cell receptor (TCR)‐dependent activation of the canonical NF‐κB signaling or expression of NF‐κB genes in rejecting allografts. Our data demonstrate that RIP2‐deficient mice have intact canonical NF‐κB signaling and can mount Th1‐mediated alloresponses and reject vascularized allografts as efficiently as wild‐type mice, thus arguing against RIP2 as a primary target for immunosuppression.

Receptor-interacting Protein-2 Deficiency Delays Macrophage Migration and Increases Intracellular Infection during Peritoneal Dialysis-associated Peritonitis

BACKGROUND Early upregulation of receptor-interacting protein-2 (RIP2) expression during peritoneal dialysis (PD)-associated peritonitis correlates with a favorable clinical outcome, while failure to upregulate RIP2 correlates with a protracted course. We noticed that patients who do not upregulate RIP2 during PD-associated peritonitis have more peritoneal macrophages during the early phase of infection. METHODS To study the mechanism behind this observation, we examined the role of RIP2 in the immune response to bacterial challenge in a mouse model of acute peritonitis. We injected RIP2(+/+) and RIP2(-/-) mice intraperitoneally with a Staphylococcus epidermidis cell free-preparation, and peritoneal cells were isolated 3, 6 and 24 h after challenge. RESULTS Surprisingly, RIP2(-/-) mice had a comparable influx of inflammatory leukocytes, but had a significantly higher number of peritoneal macrophages at 3 h, indicating delayed emigration of these cells. No significant differences were seen at later times suggesting that migration was delayed but not inhibited. In addition, RIP2(-/-) macrophages were more permissive to intracellular infection by Staphylococcus aureus, indicating that, in the absence of RIP2, resident peritoneal macrophages could become reservoirs of bacteria. CONCLUSION These findings provide a mechanism for the observation that upregulation of RIP2 expression is required for rapid resolution of peritonitis, by decreasing intracellular infection and by regulating the migration of antigen-presenting cells in the early stages of an inflammatory response.

The future of RIP2/RICK/CARDIAK as a biomarker of the inflammatory response to infection

Biological markers of disease have become increasingly important for the clinician to diagnose, predict and monitor progression, and assess the therapeutic effect of interventions on underlying pathogenic mechanisms. Robust and specific biomarkers would be very useful in inflammation, where they may facilitate early identification of tissue injury, predict disease progression and help to modify disease outcomes. However, at present, there are no robust biomarkers to predict the course of inflammation. Here, we discuss emerging data indicating that RIP2, a putative serine/threonine protein kinase, may serve as a biomarker for the resolution of peritoneal dialysis-associated peritonitis and, more generally, of the acute inflammatory response to infection.