Absent in melanoma 2 is required for innate immune recognition of Francisella tularensis.

Macrophages respond to cytosolic nucleic acids by activating cysteine protease caspase-1 within a complex called the inflammasome. Subsequent cleavage and secretion of proinflammatory cytokines IL-1beta and IL-18 are critical for innate immunity. Here, we show that macrophages from mice lacking absent in melanoma 2 (AIM2) cannot sense cytosolic double-stranded DNA and fail to trigger inflammasome assembly. Caspase-1 activation in response to intracellular pathogen Francisella tularensis also required AIM2. Immunofluorescence microscopy of macrophages infected with F. tularensis revealed striking colocalization of bacterial DNA with endogenous AIM2 and inflammasome adaptor ASC. By contrast, type I IFN (IFN-alpha and -beta) secretion in response to F. tularensis did not require AIM2. IFN-I did, however, boost AIM2-dependent caspase-1 activation by increasing AIM2 protein levels. Thus, inflammasome activation was reduced in infected macrophages lacking either the IFN-I receptor or stimulator of interferon genes (STING). Finally, AIM2-deficient mice displayed increased susceptibility to F. tularensis infection compared with wild-type mice. Their increased bacterial burden in vivo confirmed that AIM2 is essential for an effective innate immune response.

Type I IFN signaling constrains IL-17A/F secretion by gammadelta T cells during bacterial infections.

Recognition of intracellular bacteria by macrophages leads to secretion of type I IFNs. However, the role of type I IFN during bacterial infection is still poorly understood. Francisella tularensis, the causative agent of tularemia, is a pathogenic bacterium that replicates in the cytosol of macrophages leading to secretion of type I IFN. In this study, we investigated the role of type I IFNs in a mouse model of tularemia. Mice deficient for type I IFN receptor (IFNAR1(-/-)) are more resistant to intradermal infection with F. tularensis subspecies novicida (F. novicida). Increased resistance to infection was associated with a specific increase in IL-17A/F and a corresponding expansion of an IL-17A(+) gammadelta T cell population, indicating that type I IFNs negatively regulate the number of IL-17A(+) gammadelta T cells during infection. Furthermore, IL-17A-deficient mice contained fewer neutrophils compared with wild-type mice during infection, indicating that IL-17A contributes to neutrophil expansion during F. novicida infection. Accordingly, an increase in IL-17A in IFNAR1(-/-) mice correlated with an increase in splenic neutrophil numbers. Similar results were obtained in a mouse model of pneumonic tularemia using the highly virulent F. tularensis subspecies tularensis SchuS4 strain and in a mouse model of systemic Listeria monocytogenes infection. Our results indicate that the type I IFN-mediated negative regulation of IL-17A(+) gammadelta T cell expansion is conserved during bacterial infections. We propose that this newly described activity of type I IFN signaling might participate in the resistance of the IFNAR1(-/-) mice to infection with F. novicida and other intracellular bacteria.

Synovial chondromatosis affecting a digital proximal interphalangeal joint.

We present a case of synovial chondromatosis affecting the interphalangeal joint where the disease did not clearly manifest itself on pre-operative radiographs. Although rare, surgeons should consider articular synovial chondromatosis as a differential for pain and stiffness in any joint, even those of the hand.

Outcomes of four-corner arthrodesis using the Hubcap circular plate.

We present results of four-corner carpal arthrodesis with the Acumed Hubcap circular plate performed at our unit. Eight patients underwent eight procedures over five years, for scapholunate advanced collapse (five wrists) and scaphoid non-union advanced collapse (three wrists). Outcomes included range of motion, quickDASH scores, and visual analogue scores for satisfaction. At final follow-up, mean flexion-extension arc was 56°, mean radial-ulnar deviation 29° and mean quickDASH score was 23/100. Mean score for satisfaction was 7.7/10 (77%). Seven out of eight (87.5%) patients said they would have it done again, and would also recommend it to others. Radiological union was achieved in all cases. One screw broke in one arthrodesis without causing symptoms. The functional outcomes with our use of the Hubcap are comparable to those reported in literature to date with other circular plates (e.g. Spider plate). There were no non-unions, which is the main reported complication with these plates.

Differential requirement for Caspase-1 autoproteolysis in pathogen-induced cell death and cytokine processing.

Activation of the cysteine protease Caspase-1 is a key event in the innate immune response to infections. Synthesized as a proprotein, Caspase-1 undergoes autoproteolysis within multiprotein complexes called inflammasomes. Activated Caspase-1 is required for proteolytic processing and for release of the cytokines interleukin-1ß and interleukin-18, and it can also cause rapid macrophage cell death. We show that macrophage cell death and cytokine maturation in response to infection with diverse bacterial pathogens can be separated genetically and that two distinct inflammasome complexes mediate these events. Inflammasomes containing the signaling adaptor Asc form a single large "focus" in which Caspase-1 undergoes autoproteolysis and processes IL-1ß/IL-18. In contrast, Asc-independent inflammasomes activate Caspase-1 without autoproteolysis and do not form any large structures in the cytosol. Caspase-1 mutants unable to undergo autoproteolysis promoted rapid cell death, but processed IL-1ß/18 inefficiently. Our results suggest the formation of spatially and functionally distinct inflammasomes complexes in response to bacterial pathogens.

In vitro polymerization of a functional Escherichia coli amyloid protein.

Amyloid formation is characterized by the conversion of soluble proteins into biochemically and structurally distinct fibers. Although amyloid formation is traditionally associated with diseases such as Alzheimer disease, a number of biologically functional amyloids have recently been described. Curli are amyloid fibers produced by Escherichia coli that contribute to biofilm formation and other important physiological processes. We characterized the polymerization properties of the major curli subunit protein CsgA. CsgA polymerizes into an amyloid fiber in a sigmoidal kinetic fashion with a distinct lag, growth, and stationary phase. Adding sonicated preformed CsgA fibers to the polymerization reaction can significantly shorten the duration of the lag phase. We also demonstrate that the conversion of soluble CsgA into an insoluble fiber involves the transient formation of an intermediate similar to that characterized for several disease-associated amyloids. The CsgA core amyloid domain can be divided into five repeating units that share sequence and structural hallmarks. We show that peptides representing three of these repeating units are amyloidogenic in vitro. Although the defining characteristics of CsgA polymerization appear conserved with disease-associated amyloids, these proteins evolved in diverse systems and for different purposes. Therefore, amyloidogenesis appears to be an innate protein folding pathway that can be capitalized on to fulfill normal physiological tasks.

Combined thigh flap for closure of massive trunk defect.

A massive trunk defect resulting from resection of recurrent sarcoma was reconstructed with a combined free flap incorporating medial, anterior, and lateral thigh tissues. This flap included the tensor fasciae latae, lateral thigh perforator, and rectus femoris, all based on the lateral femoral circumflex pedicle. A saphenous vein conduit enabled this flap to replace resected tissues at the lower thorax. Combining the three different commonly used thigh flaps on a single large pedicle enabled transfer of a 47.5 x 33.5-cm mega-flap.

Reconstruction of a complex hemifacial deformity with multiple simultaneous free-flap transfers: case report.

Severe disfigurement, facial paralysis, abnormal continuity of oral and nasal passages, and velopharyngeal incompetence resulted, following maxillectomy and cranial-base resection for a radiation-induced sarcoma. Oral lining, bone support, facial muscle, and outer skin were provided with a single-staged transfer of radial forearm, scapular bone, scapular skin, and serratus anterior muscle with anastamoses to the contralateral neck. This combination of flaps may be considered in complex facial deformities, and may obviate the need for staged prefabrication.

Reinnervated medial gastrocnemius free flap for closure of a recurrent ischial pressure sore: case report.

A 42-year-old T7 level paraplegic man had undergone multiple local flap transfers for closure of a recurrent left ischial pressure sore. When wound breakdown again occurred and regional flap transfers were no longer a possibility, a medial gastrocnemius free flap was transferred to the ischial region. Reinnervation of this flap was accomplished by interposing a sural nerve graft between a proximal intercostal nerve and the tibial motor nerve branch of the gastrocnemius muscle. Following the return of protective sensation, the patient has developed no new ischial pressure ulcerations.