Mannose receptor-derived peptides neutralize pore-forming toxins and reduce inflammation and development of pneumococcal disease.

Cholesterol-dependent cytolysins (CDCs) are essential virulence factors for many human pathogens like Streptococcus pneumoniae (pneumolysin, PLY), Streptococcus pyogenes (streptolysin O, SLO), and Listeria monocytogenes (Listeriolysin, LLO) and induce cytolysis and inflammation. Recently, we identified that pneumococcal PLY interacts with the mannose receptor (MRC-1) on specific immune cells thereby evoking an anti-inflammatory response at sublytic doses. Here, we identified the interaction sites between MRC-1 and CDCs using computational docking. We designed peptides from the CTLD4 domain of MRC-1 that binds to PLY, SLO, and LLO, respectively. In vitro, the peptides blocked CDC-induced cytolysis and inflammatory cytokine production by human macrophages. Also, they reduced PLY-induced damage of the epithelial barrier integrity as well as blocked bacterial invasion into the epithelium in a 3D lung tissue model. Pre-treatment of human DCs with peptides blocked bacterial uptake via MRC-1 and reduced intracellular bacterial survival by targeting bacteria to autophagosomes. In order to use the peptides for treatment in vivo, we developed calcium phosphate nanoparticles (CaP NPs) as peptide nanocarriers for intranasal delivery of peptides and enhanced bioactivity. Co-administration of peptide-loaded CaP NPs during infection improved survival and bacterial clearance in both zebrafish and mice models of pneumococcal infection. We suggest that MRC-1 peptides can be employed as adjunctive therapeutics with antibiotics to treat bacterial infections by countering the action of CDCs.

Emerging concepts in the pathogenesis of the Streptococcus pneumoniae: From nasopharyngeal colonizer to intracellular pathogen.

Streptococcus pneumoniae (the pneumococcus) is a human respiratory tract pathogen and a major cause of morbidity and mortality globally. Although the pneumococcus is a commensal bacterium that colonizes the nasopharynx, it also causes lethal diseases such as meningitis, sepsis, and pneumonia, especially in immunocompromised patients, in the elderly, and in young children. Due to the acquisition of antibiotic resistance and the emergence of nonvaccine serotypes, the pneumococcus has been classified as one of the priority pathogens for which new antibacterials are urgently required by the World Health Organization, 2017. Understanding molecular mechanisms behind the pathogenesis of pneumococcal infections and bacterial interactions within the host is crucial to developing novel therapeutics. Previously considered to be an extracellular pathogen, it is becoming evident that pneumococci may also occasionally establish intracellular niches within the body to escape immune surveillance and spread within the host. Intracellular survival within host cells also enables pneumococci to resist many antibiotics. Within the host cell, the bacteria exist in unique vacuoles, thereby avoiding degradation by the acidic lysosomes, and modulate the expression of its virulence genes to adapt to the intracellular environment. To invade and survive intracellularly, the pneumococcus utilizes a combination of virulence factors such as pneumolysin (PLY), pneumococcal surface protein A (PspA), pneumococcal adhesion and virulence protein B (PavB), the pilus-1 adhesin RrgA, pyruvate oxidase (SpxB), and metalloprotease (ZmpB). In this review, we discuss recent findings showing the intracellular persistence of Streptococcus pneumoniae and its underlying mechanisms.

Cinobufagin Modulates Human Innate Immune Responses and Triggers Antibacterial Activity.

The traditional Chinese medicine Chan-Su is widely used for treatment of cancer and cardiovascular diseases, but also as a remedy for infections such as furunculosis, tonsillitis and acute pharyngitis. The clinical use of Chan-Su suggests that it has anti-infective effects, however, the mechanism of action is incompletely understood. In particular, the effect on the human immune system is poorly defined. Here, we describe previously unrecognized immunomodulatory activities of cinobufagin (CBG), a major bioactive component of Chan-Su. Using human monocyte-derived dendritic cells (DCs), we show that LPS-induced maturation and production of a number of cytokines was potently inhibited by CBG, which also had a pro-apoptotic effect, associated with activation of caspase-3. Interestingly, CBG triggered caspase-1 activation and significantly enhanced IL-1ß production in LPS-stimulated cells. Finally, we demonstrate that CBG upregulates gene expression of the antimicrobial peptides (AMPs) hBD-2 and hBD-3 in DCs, and induces secretion of HNP1-3 and hCAP-18/LL-37 from neutrophils, potentiating neutrophil antibacterial activity. Taken together, our data indicate that CBG modulates the inflammatory phenotype of DCs in response to LPS, and triggers an antibacterial innate immune response, thus proposing possible mechanisms for the clinical effects of Chan-Su in anti-infective therapy.

Preferential silent survival of intracellular bacteria in hemoglobin-primed macrophages.

Hemolysis releases hemoglobin (Hb), a prooxidant, into circulation. While the heme iron is a nutrient for the invading pathogens, it releases ROS, which is both microbicidal and cytotoxic, making it a double-edged sword. Previously, we found a two-pass detoxification mechanism involving the endocytosis of Hb into monocytes in collaboration with vascular endothelial cells to overcome oxidative damage. This prompted us to examine the effect of Hb priming on host cell viability and intracellular bacterial clearance during a hemolytic infection. Here, we demonstrate that Hb-primed macrophages harbor a higher intracellular bacterial load but with suppressed apoptosis. p-ERK and p-p38 MAPK were significantly downregulated, with concomitant impairment of Bax and downstream caspases. The Hb-primed cells harboring intracellular bacteria upregulated anti-inflammatory IL-10 and downregulated proinflammatory TNF-α, which further enhanced the infectivity of the neighboring cells. Our findings suggest that opportunistic intracellular pathogens exploit the Hb-scavenging machinery of the host to silently persist within the circulating phagocytes by suppressing apoptosis while escaping immune surveillance.

Chondroblastoma of the talus.

We report the case of a 13-year-old male child who presented with a painful left ankle. On imaging (radiography and computed tomography scan with 3-dimensional reconstruction views), an osteolytic lesion in the body of the talus was revealed. Open biopsy, curettage, and fibular bone grafting were done, and the specimen was sent for histopathologic examination. The histopathologic report confirmed the specimen to be chondroblastoma of the talus bone. Chondroblastoma is a rare benign cartilaginous neoplasm that accounts for approximately 1% of all bone tumors and characteristically arises in the epiphysis of a long bone, particularly the humerus, tibia, and femur. Chondroblastoma can affect people of all ages. It is, however, most common in children and young adults aged 10 to 20 years. Chondroblastoma in a tarsal bone is a rare entity. Managing chondroblastoma of the talus with curettage and bone grafting has shown good outcomes.

CD163 and IgG codefend against cytotoxic hemoglobin via autocrine and paracrine mechanisms.

Lysis of RBCs during numerous clinical settings such as severe hemolytic anemia, infection, tissue injury, or blood transfusion releases the endogenous damage-associated molecular pattern, hemoglobin (Hb), into the plasma. The redox-reactive Hb generates cytotoxic reactive oxygen species, disrupting the redox balance and impairing the immune-responsive blood cells. Therefore, it is crucial to understand how the immune system defends against the cytotoxic Hb. We identified a shortcut "capture and quench" mechanism of detoxification of Hb by the monocyte scavenger receptor CD163, independent of the well-known dominant antioxidant, haptoglobin. Our findings support a highly efficient two-pass mechanism of detoxification and clearance of Hb: 1) a direct suppression of Hb-pseudoperoxidase activity by CD163, involving an autocrine loop of CD163 shedding, sequestration of Hb, recycling, and homeostasis of CD163 in human monocytes and 2) paracrine transactivation of endothelial cells by the shedded soluble CD163 (sCD163), which further detoxifies and clears residual Hb. We showed that sCD163 and IgG interact with free Hb in the plasma and subsequently the sCD163-Hb-IgG complex is endocytosed into monocytes via FcγR. The endocytosed sCD163 is recycled to restore the homeostasis of CD163 on the monocyte membrane in an autocrine cycle, whereas the internalized Hb is catabolized. Using ex vivo coculture experiments, we demonstrated that the monocyte-derived sCD163 and IgG shuttle residual plasma Hb into the proximal endothelial cells. These findings suggest that CD163 and IgG collaborate to engage monocytes and endothelial cells in a two-pass detoxification mechanism to mount a systemic defense against Hb-induced oxidative stress.

Epithelioid hemangioendothelioma of the proximal phalanx of the left second toe - a rare occurence.

INTRODUCTION: Epithelioid hemangioendothelioma (EHE) of the bone is extremely rare and occurs predominantly in males. It most frequently occurs during the second and third decades of life. The lower extremities are most commonly involved. We describe a diagnostically challenging case of epithelioid hemangioendothelioma of proximal phalanx of 2nd toe of left foot with histological features reminiscent of osteoblastomatosis. CASE REPORT: A 52 year old man presented with history of intermittent pain with swelling in second toe since 6 months. Radiograph showed a lytic lesion in proximal phalanx of the great toe. CT and MRI reported non specific lesion in the toe. Pain was quite severe and as the patient was a labourer and wanted to get back to his work as soon as possible a decision of disarticulation of the second toe at metatarsophalnageal joint was taken. Histopathology confirmed the diagnosis of Epithelioid hemangioendothelioma and patient was called for regular follow up. There are no complications and recurrence at two year follow up. CONCLUSION: EHE of the bone is extremely rare vascular tumor. To our knowledge, this is the first case of EHE with such features. EHE should be kept as one of the important differential diagnosis while diagnosing vascular tumors. Careful attention to the histopathological features is necessary for the confirmation of the diagnosis.