Biology subjects

Aerts, P.

Publications and source records attributed to Aerts, P..

7 recordsLinked to original sources

bioRxiv2026

C1q-mediated steric hindrance limits FcγR contribution to antibody-driven phagocytosis by human neutrophils

Phagocytosis and killing of bacteria by neutrophils is a key driver of human immunity against invading infections. IgG antibodies targeting the bacterial surface can potently enhance phagocytic uptake by engaging Fc gamma receptors (Fc{gamma}Rs) on the neutrophil membrane. In addition, IgG-mediated complement activation triggers surface deposition of complement opsonins that engage complement receptors (CRs) to further enhance target cell clearance. In this paper, we reveal that complement deposition prevents engagement of Fc{gamma}Rs to the Fc-domain of surface-bound IgG molecules. When complement is present, we observe that blockade of Fc{gamma}Rs does not influence phagocytosis of both Gram-positive and -negative bacteria (using Staphylococcus aureus and Klebsiella pneumoniae as model organisms). Complement-mediated hindrance of Fc{gamma}R engagement was observed in different model conditions, for example using either pre-existing polyclonal antibodies in human serum or recombinant monoclonal antibodies (mAbs) targeting different bacterial antigens. Using Fc engineering, we found that inhibition of Fc{gamma}R binding is dependent on the ability of IgGs to form IgG hexamers. Mechanistically, we show that complement proteins, in particular C1q, directly prevents the interaction between IgG-Fc and Fc{gamma}R by steric hindrance. Together, these insights help us define the respective roles of Fc{gamma}R and CR in neutrophil phagocytosis, while also providing important fundamental insights for therapeutic antibody development.

immunology↗

bioRxiv2024

Joint and tissue mechanics in post-traumatic osteoarthritis: insights from the rat model

ObjectiveAltered mechanical loading is a known risk factor for osteoarthritis. Destabilization of the medial meniscus (DMM) is a preclinical gold standard model for post-traumatic osteoarthritis and is thought to induce instability and locally increased loading. However, the joint- and tissue-level mechanical environment underlying cartilage degeneration remains poorly documented. DesignUsing a custom multiscale modeling approach, we assessed joint and tissue biomechanics in rats undergoing sham surgery and DMM. High-fidelity experimental gait data were collected in a setup combining biplanar fluoroscopy and a ground reaction force plate. Knee poses and joint-level loading were estimated through musculoskeletal modeling, using bony landmarks, semi-automatically tracked via deep learning on fluoroscopic images, and ground reaction forces. A musculoskeletal model of the rat hindlimb was adapted to represent knee flexion-extension, valgus-varus, and internal-external rotation. The tissue-level cartilage mechanical environment was then spatially estimated, using the musculoskeletal modeling parameters as inputs into a dedicated finite element (FE) model of the rat knee, comprising cartilage and meniscal tissues. Experimental gait data and modeling workflows, including musculoskeletal models and FE meshes, are openly shared through a data repository. ResultsIn rats with DMM, the frontal plane knee pose was altered, yet there was no indication of joint-level overloading. Tissue-level mechanical cues typically linked with cartilage degeneration were not increased in the medial tibial cartilage, despite evidence of tissue structural changes. ConclusionDMM did not increase joint and tissue mechanical responses in the knee medial compartment, suggesting that mechanical loading alone does not explain the observed osteoarthritis-like structural changes.

bioengineering↗

bioRxiv2022

Probabilistic Modeling Confirms Delayed, But Non-Deficient Locomotor Development in Low Birth Weight Piglets

1Locomotor kinematics have been challenging inputs for automated diagnostic screening of livestock. Locomotion is a highly variable behavior, and influenced by subject characteristics (e.g. body mass, size, age, disease). We assemble a set of methods from different scientific disciplines, composing an automatic, high through-put workflow which can disentangle behavioral complexity and generate precise individual indicators of non-normal behavior for application in diagnostics and research. For this study, piglets (Sus domesticus) were filmed from lateral perspective during their first ten hours of life, an age at which maturation is quick and body mass and size have major consequences for survival. We then apply deep learning methods for point digitization, calculate joint angle profiles, and apply information-preserving transformations to retrieve a multivariate kinematic data set. We train probabilistic models to infer subject characteristics from kinematics. Model accuracy is validated for strides from piglets of normal birth weight (i.e. the category it was trained on), but the models infer the body mass and size of low birth weight piglets (which were left out of training, out-of-sample inference) to be "normal". The age of some (but not all) low birth weight individuals is underestimated, indicating developmental delay. Such individuals could be identified automatically, inspected, and treated accordingly. This workflow has potential for automatic, precise screening in livestock management.

zoology↗

bioRxiv2022

Promoting Fc-Fc interactions between anti-capsular antibodies provides strong complement-dependent immune protection against Streptococcus pneumoniae

Streptococcus pneumoniae 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 reinforce 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. Here we investigate whether mAbs can be used to induce killing of pneumococcal serotypes for which the current vaccines show unsuccessful protection. Our study demonstrates that when human mAbs against pneumococcal capsule polysaccharides (CPS) have a poor capacity to induce complement activation, a critical process for immune protection against pneumococci, their activity can be strongly improved by hexamerization-enhancing mutations. Our data indicate that anti-capsular antibodies may have a low capacity to form higher-order oligomers (IgG hexamers) that are needed to recruit complement component C1. Indeed, specific point mutations in the IgG-Fc domain that strengthen hexamerization strongly enhance C1 recruitment and downstream complement activation on encapsulated pneumococci. Specifically, hexamerization-enhancing mutations E430G or E345K in CPS6-IgG strongly potentiate complement activation on S. pneumoniae strains that express capsular serotype 6 (CPS6), and the highly invasive serotype 19A strain. Furthermore, these mutations improve complement activation via mAbs recognizing CPS3 and CPS8 strains. Importantly, hexamer-enhancing mutations enable mAbs to induce strong phagocytosis and intracellular killing by human neutrophils. Finally, passive immunization with CPS6-IgG1-E345K protected mice from developing severe pneumonia. Altogether, this work provides an important proof-of-concept for future optimization of antibody therapies against encapsulated bacteria.

microbiology↗

bioRxiv2021

C1q binding to surface-bound IgG is stabilized by C1r2s2 proteases

Complement is an important effector mechanism for antibody-mediated clearance of infections and tumor cells. Upon binding to target cells, the antibodys constant (Fc) domain recruits complement component C1 to initiate a proteolytic cascade that generates lytic pores and stimulates phagocytosis. The C1 complex (C1qr2s2) consists of the large recognition protein C1q and a heterotetramer of proteases C1r and C1s (C1r2s2). While interactions between C1 and IgG-Fcs are believed to be mediated by the globular heads of C1q, we here find that C1r2s2 proteases affect the capacity of C1q to form an avid complex with surface-bound IgG molecules (on various DNP-coated surfaces and pathogenic Staphylococcus aureus). The extent to which C1r2s2 contribute to C1q-IgG stability strongly differs between human IgG subclasses. Using antibody engineering of monoclonal IgG we reveal that hexamer-enhancing mutations improve C1q-IgG stability, both in absence and presence of C1r2s2. In addition, hexamer-enhanced IgGs targeting S. aureus mediate improved complement-dependent phagocytosis by human neutrophils. Altogether, these molecular insights into complement binding to surface-bound IgGs could be important for optimal design of antibody therapies.

immunology↗

bioRxiv2020

The impact of Staphylococcus aureus cell wall glycosylation on langerin recognition and Langerhans cell activation

Staphylococcus aureus is the leading cause of skin and soft tissue infections. It remains incompletely understood how skin-resident immune cells respond to S. aureus invasion and contribute to an effective immune response. Langerhans cells (LCs), the only professional antigen-presenting cell type in the epidermis, sense S. aureus through their pattern-recognition receptor langerin, triggering a pro-inflammatory response. Langerin specifically recognizes the {beta}-1,4-linked N-acetylglucosamine ({beta}-GlcNAc) modification, which requires the glycosyltransferase TarS, on the cell wall glycopolymer Wall Teichoic Acid (WTA). Recently, an alternative WTA glycosyltransferase, TarP, was identified in methicillin-resistant S. aureus strains belonging to clonal complexes (CC) 5 and CC398. TarP also modifies WTA with {beta}-GlcNAc but at the C-3 position of the WTA ribitol phosphate (RboP) subunit. Here, we aimed to unravel the impact of {beta}-GlcNAc linkage position for langerin binding and LC activation. In addition, we performed structure-binding studies using a small panel of unique chemically-synthesized WTA molecules to assess langerin-WTA binding requirements. Using FITC-labeled recombinant human langerin and genetically-modified S. aureus strains, we observed that langerin similarly recognized bacteria that produce either TarS- or TarP-modified WTA. Furthermore, using chemically-synthesized WTA, representative of the different S. aureus WTA glycosylation patterns, established that {beta}-GlcNAc is sufficient to confer langerin binding. Functionally, tarP-expressing S. aureus induce increased cytokine production and maturation of in vitro-generated LCs compared to tarSexpressing S. aureus. Overall, our data suggest that LCs are able to sense all {beta}-GlcNAc-WTA producing S. aureus strains, likely performing an important role as first responders upon S. aureus skin invasion.

microbiology↗

bioRxiv2020

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

IgG 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 to 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. Here we show that Staphylococcal protein A (SpA), an important virulence factor and vaccine candidate of Staphylococcus aureus, effectively blocks IgG hexamerization and subsequent complement activation. Using native mass spectrometry and high-speed atomic force microscopy, we demonstrate that SpA blocks IgG hexamerization through competitive binding to the Fc-Fc interaction interface on IgG monomers. In concordance, we show that SpA interferes with the formation of (IgG)6:C1q complexes and prevents downstream complement activation on the surface of S. aureus. Lastly, we demonstrate that IgG3 antibodies against S. aureus can potently induce complement activation even in the presence of SpA. Altogether, this study identifies SpA as an immune evasion protein that specifically blocks IgG hexamerization.

microbiology↗