The pluripotency of embryonic stem (ES) cells is thought to be maintained by a few key transcription factors, including Oct3/4 and Sox2. The function of Oct3/4 in ES cells has been extensively characterized, but that of Sox2 has yet to be determined. Sox2 can act synergistically with Oct3/4 in vitro to activate Oct-Sox enhancers, which regulate the expression of pluripotent stem cell-specific genes, including Nanog, Oct3/4 and Sox2 itself. These findings suggest that Sox2 is required by ES cells for its Oct-Sox enhancer activity. Using inducible Sox2-null mouse ES cells, we show that Sox2 is dispensable for the activation of these Oct-Sox enhancers. In contrast, we demonstrate that Sox2 is necessary for regulating multiple transcription factors that affect Oct3/4 expression and that the forced expression of Oct3/4 rescues the pluripotency of Sox2-null ES cells. These results indicate that the essential function of Sox2 is to stabilize ES cells in a pluripotent state by maintaining the requisite level of Oct3/4 expression.

K/BxN T cell receptor transgenic mice are a model of inflammatory arthritis, similar to rheumatoid arthritis. Disease in these animals is focused specifically on the joints but stems from autoreactivity to a ubiquitously expressed antigen, glucose-6-phosphate isomerase (GPI). T and B cells are both required for disease initiation, but anti-GPI immunoglobulins (Igs), alone, can induce arthritis in lymphocyte-deficient recipients. Here, we show that the arthritogenic Igs act through both Fc receptors (in particular, FcgammaRIII) and the complement network (C5a). Surprisingly, the alternative pathway of complement activation is critical, while classical pathway components are entirely dispensable. We suggest that autoimmune disease, even one that is organ specific, can occur when mobilization of an adaptive immune response results in runaway activation of the innate response.

Phagocyte recognition and clearance of bacteria play essential roles in the host response to infection. In an on-going forward genetic screen, we identify the Drosophila melanogaster scavenger receptor Croquemort as a receptor for Staphylococcus aureus, implicating for the first time the CD36 family as phagocytic receptors for bacteria. In transfection assays, the mammalian Croquemort paralogue CD36 confers binding and internalization of Gram-positive and, to a lesser extent, Gram-negative bacteria. By mutational analysis, we show that internalization of S. aureus and its component lipoteichoic acid requires the COOH-terminal cytoplasmic portion of CD36, specifically Y463 and C464, which activates Toll-like receptor (TLR) 2/6 signaling. Macrophages lacking CD36 demonstrate reduced internalization of S. aureus and its component lipoteichoic acid, accompanied by a marked defect in tumor necrosis factor-α and IL-12 production. As a result, Cd36 −/− mice fail to efficiently clear S. aureus in vivo resulting in profound bacteraemia. Thus, response to S. aureus requires CD36-mediated phagocytosis triggered by the COOH-terminal cytoplasmic domain, which initiates TLR2/6 signaling.

Gram-positive organisms like Staphylococcus aureus are a major cause of morbidity and mortality worldwide. Humoral response molecules together with phagocytes play a role in host responses to S. aureus. The mannose-binding lectin (MBL, also known as mannose-binding protein) is an oligomeric serum molecule that recognizes carbohydrates decorating a broad range of infectious agents including S. aureus. Circumstantial evidence in vitro and in vivo suggests that MBL plays a key role in first line host defense. We tested this contention directly in vivo by generating mice that were devoid of all MBL activity. We found that 100% of MBL-null mice died 48 h after exposure to an intravenous inoculation of S. aureus compared with 45% mortality in wild-type mice. Furthermore, we demonstrated that neutrophils and MBL are required to limit intraperitoneal infection with S. aureus. Our study provides direct evidence that MBL plays a key role in restricting the complications associated with S. aureus infection in mice and raises the idea that the MBL gene may act as a disease susceptibility gene against staphylococci infections in humans.

Here we describe a blood-cleansing device for sepsis therapy inspired by the spleen, which can continuously remove pathogens and toxins from blood without first identifying the infectious agent. Blood flowing from an infected individual is mixed with magnetic nanobeads coated with an engineered human opsonin--mannose-binding lectin (MBL)--that captures a broad range of pathogens and toxins without activating complement factors or coagulation. Magnets pull the opsonin-bound pathogens and toxins from the blood; the cleansed blood is then returned back to the individual. The biospleen efficiently removes multiple Gram-negative and Gram-positive bacteria, fungi and endotoxins from whole human blood flowing through a single biospleen unit at up to 1.25 liters per h in vitro. In rats infected with Staphylococcus aureus or Escherichia coli, the biospleen cleared >90% of bacteria from blood, reduced pathogen and immune cell infiltration in multiple organs and decreased inflammatory cytokine levels. In a model of endotoxemic shock, the biospleen increased survival rates after a 5-h treatment.