Glycan-specific IgM is critical for human immunity to Staphylococcus aureus.

Staphylococcus aureus is a major human pathogen, yet the immune factors that protect against infection remain elusive. High titers of opsonic IgG antibodies, achieved in preclinical animal immunization studies, have consistently failed to provide protection in humans. Here, we investigate antibody responses to the conserved S.

Agnostic B cell selection approach identifies antibodies against K. pneumoniae that synergistically drive complement activation.

Antibody-dependent complement activation plays a key role in the natural human immune response to infections. Currently, the understanding of which antibody-antigen combinations drive a potent complement response on bacteria is limited. Here, we develop an antigen-agnostic approach to stain and single-cell sort human IgG memory B cells recognizing intact bacterial cells, keeping surface antigens in their natural context.

Photoimmuno-antimicrobial therapy for Staphylococcus aureus implant infection.

Introduction: Implant infections caused by Staphylococcus aureus are responsible for high mortality and morbidity worldwide. Treatment of these infections can be difficult especially when bacterial biofilms are involved. In this study we investigate the potential of infrared photoimmunotherapy to eradicate staphylococcal infection in a mouse model.

CD5L is a canonical component of circulatory IgM.

Immunoglobulin M (IgM) is an evolutionary conserved key component of humoral immunity, and the first antibody isotype to emerge during an immune response. IgM is a large (1 MDa), multimeric protein, for which both hexameric and pentameric structures have been described, the latter additionally containing a joining (J) chain. Using a combination of single-particle mass spectrometry and mass photometry, proteomics, and immunochemical assays, we here demonstrate that circulatory (serum) IgM exclusively exists as a complex of J-chain-containing pentamers covalently bound to the small (36 kDa) protein CD5 antigen-like (CD5L, also called apoptosis inhibitor of macrophage).

Artificial surface labelling of Escherichia coli with StrepTagII antigen to study how monoclonal antibodies drive complement-mediated killing.

Antibodies play a key role in the immune defence against Gram-negative bacteria. After binding to bacterial surface antigens, IgG and IgM can activate the complement system and trigger formation of lytic membrane attack complex (MAC) pores. Molecular studies to compare functional activity of antibodies on bacteria are hampered by the limited availability of well-defined antibodies against bacterial surface antigens.

Promoting Fc-Fc interactions between anti-capsular antibodies provides strong immune protection against .

is the leading cause of community-acquired pneumonia and an important cause of childhood mortality. Despite the introduction of successful vaccines, the global spread of both non-vaccine serotypes and antibiotic-resistant strains reinforces the development of alternative therapies against this pathogen. One possible route is the development of monoclonal antibodies (mAbs) that induce killing of bacteria via the immune system.

Toward Understanding How Staphylococcal Protein A Inhibits IgG-Mediated Phagocytosis.

IgG molecules are crucial for the human immune response against bacterial infections. IgGs can trigger phagocytosis by innate immune cells, like neutrophils. To do so, IgGs should bind to the bacterial surface via their variable Fab regions and interact with Fcγ receptors and complement C1 via the constant Fc domain.

Monoclonal antibodies effectively potentiate complement activation and phagocytosis of in neonatal human plasma.

Central line associated bloodstream infections (CLABSI) with are a major cause of morbidity in neonates, who have an increased risk of infection because of their immature immune system. As especially preterm neonates suffer from antibody deficiency, clinical studies into preventive therapies have thus far focused on antibody supplementation with pooled intravenous immunoglobulins from healthy donors (IVIG) but with little success. Here we study the potential of monoclonal antibodies (mAbs) against to induce phagocytic killing by human neutrophils.

Correction: Polymerization of C9 enhances bacterial cell envelope damage and killing by membrane attack complex pores.

[This corrects the article DOI: 10.1371/journal.ppat.

Human monoclonal antibodies against surface antigens recognize in vitro and in vivo biofilm.

Implant-associated infections are difficult to treat because of biofilm formation. Bacteria in a biofilm are often insensitive to antibiotics and host immunity. Monoclonal antibodies (mAbs) could provide an alternative approach to improve the diagnosis and potential treatment of biofilm-related infections.

Polymerization of C9 enhances bacterial cell envelope damage and killing by membrane attack complex pores.

Complement proteins can form membrane attack complex (MAC) pores that directly kill Gram-negative bacteria. MAC pores assemble by stepwise binding of C5b, C6, C7, C8 and finally C9, which can polymerize into a transmembrane ring of up to 18 C9 monomers. It is still unclear if the assembly of a polymeric-C9 ring is necessary to sufficiently damage the bacterial cell envelope to kill bacteria.

Method for Depletion of IgG and IgM from Human Serum as Naive Complement Source.

Understanding how human complement proteins interact with human antibodies is important for the development of antibody therapies and understanding autoimmune diseases. At present, many groups use baby rabbit serum as a source of complement because, in contrast to human serum, it lacks preexisting antibodies. However, for characterization of human (monoclonal) antibodies, human serum would be a preferred source of complement.

Impact of Glycan Linkage to Wall Teichoic Acid on Langerin Recognition and Langerhans Cell Activation.

is the leading cause of skin and soft tissue infections. It remains incompletely understood how skin-resident immune cells respond to invading and contribute to an effective immune response. Langerhans cells (LCs), the only professional antigen-presenting cell type in the epidermis, sense through their pattern-recognition receptor langerin, triggering a proinflammatory response.

Staphylococcal protein A inhibits complement activation by interfering with IgG hexamer formation.

Immunoglobulin (Ig) G molecules are essential players in the human immune response against bacterial infections. An important effector of IgG-dependent immunity is the induction of complement activation, a reaction that triggers a variety of responses that help kill bacteria. Antibody-dependent complement activation is promoted by the organization of target-bound IgGs into hexamers that are held together via noncovalent Fc-Fc interactions.

The Orphan Immune Receptor LILRB3 Modulates Fc Receptor-Mediated Functions of Neutrophils.

Neutrophils are critical to the generation of effective immune responses and for killing invading microbes. Paired immune receptors provide important mechanisms to modulate neutrophil activation thresholds and effector functions. Expression of the leukocyte Ig-like receptor (LILR)A6 (ILT8/CD85b) and LILRB3 (ILT5/CD85a) paired-receptor system on human neutrophils has remained unclear because of the lack of specific molecular tools.

Functional Characterization of Alternative and Classical Pathway C3/C5 Convertase Activity and Inhibition Using Purified Models.

Complement is essential for the protection against infections; however, dysregulation of complement activation can cause onset and progression of numerous inflammatory diseases. Convertase enzymes play a central role in complement activation and produce the key mediators of complement: C3 convertases cleave C3 to generate chemoattractant C3a and label target cells with C3b, which promotes phagocytosis; C5 convertases cleave C5 into chemoattractant C5a, and C5b, which drives formation of the membrane attack complex. Since convertases mediate nearly all complement effector functions, they are ideal targets for therapeutic complement inhibition.

Identification of a staphylococcal complement inhibitor with broad host specificity in equid strains.

is a versatile pathogen capable of causing a broad range of diseases in many different hosts. can adapt to its host through modification of its genome ( by acquisition and exchange of mobile genetic elements that encode host-specific virulence factors). Recently, the prophage φSaeq1 was discovered in strains from six different clonal lineages almost exclusively isolated from equids.

LukMF' is the major secreted leukocidin of bovine Staphylococcus aureus and is produced in vivo during bovine mastitis.

Staphylococcus aureus is a major human and animal pathogen and a common cause of mastitis in cattle. S. aureus secretes several leukocidins that target bovine neutrophils, crucial effector cells in the defence against bacterial pathogens.

Molecular insights into the surface-specific arrangement of complement C5 convertase enzymes.

Background: Complement is a large protein network in plasma that is crucial for human immune defenses and a major cause of aberrant inflammatory reactions. The C5 convertase is a multi-molecular protease complex that catalyses the cleavage of native C5 into its biologically important products. So far, it has been difficult to study the exact molecular arrangement of C5 convertases, because their non-catalytic subunits (C3b) are covalently linked to biological surfaces through a reactive thioester.

Structural basis for inhibition of TLR2 by staphylococcal superantigen-like protein 3 (SSL3).

Toll-like receptors (TLRs) are crucial in innate recognition of invading micro-organisms and their subsequent clearance. Bacteria are not passive bystanders and have evolved complex evasion mechanisms. Staphylococcus aureus secretes a potent TLR2 antagonist, staphylococcal superantigen-like protein 3 (SSL3), which prevents receptor stimulation by pathogen-associated lipopeptides.

The staphylococcal toxin Panton-Valentine Leukocidin targets human C5a receptors.

Panton-Valentine Leukocidin (PVL) is a staphylococcal bicomponent pore-forming toxin linked to severe invasive infections. Target-cell and species specificity of PVL are poorly understood, and the mechanism of action of this toxin in Staphylococcus aureus virulence is controversial. Here, we identify the human complement receptors C5aR and C5L2 as host targets of PVL, mediating both toxin binding and cytotoxicity.

Functional basis for complement evasion by staphylococcal superantigen-like 7.

The human pathogen Staphylococcus aureus has a plethora of virulence factors that promote its colonization and survival in the host. Among such immune modulators are staphylococcal superantigen-like (SSL) proteins, comprising a family of 14 small, secreted molecules that seem to interfere with the host innate immune system. SSL7 has been described to bind immunoglobulin A (IgA) and complement C5, thereby inhibiting IgA-FcαRI binding and serum killing of Escherichia coli.