Biology subjects

Stadtmueller, B. M.

Publications and source records attributed to Stadtmueller, B. M..

7 recordsLinked to original sources

bioRxiv2026

Structural insights into antibody responses against influenza A virus in its natural reservoir

While influenza A virus undergoes rapid antigenic drift in humans, at least some subtypes, such as H3, have relatively stable antigenicity in natural waterfowl reservoirs, despite the presence of immune pressure. However, the underlying mechanisms remain poorly understood. This study identified and characterized 187 antibodies to H3 hemagglutinin from experimentally infected mallard ducks, 18 of which were further analyzed by cryo-EM. Compared with human H3 antibodies, duck H3 antibodies exhibited higher glycan-binding propensity, more balanced immunodominance hierarchy, and targeted distinct epitopes. Other unique features of duck H3 antibodies included a convergent CDR H3-independent heavy chain-only binding mode and an N-glycosylated CDR H3 as decoy receptor. By annotating duck immunoglobulin germline genes, we also demonstrated the importance of gene conversion in duck H3 antibodies. Overall, our findings provide insights into how millennia of coevolution have shaped the interplay between influenza A virus antigenic drift and antibody responses in the natural reservoir.

immunology↗

bioRxiv2025

The structures of tetrameric Avian Immunoglobulin A are uniquely structured to support mucosal immunity

Birds and mammals assemble polymeric (p) forms of immunoglobulin (Ig) A, which are transported to mucosal surfaces and released as secretory (S) IgA, the predominant mucosal antibody. Mammalian SIgA, which is typically dimeric, is well characterized; however, avian IgA structure-function relationships and how they compare to those in mammals remains unclear. Here we report the cryo-electron microscopy structures of mallard duck pIgA and SIgA at 3.76-[A] and 3.21-[A] resolution, respectively. Both structures revealed four IgA monomers linked through one joining chain (JC) and adopted a non-planar conformation; a heavy chain domain absent in mammals, extended the tetramers non-planar geometry toward antigen binding sites. The SIgA structure revealed four secretory component (SC) domains binding IgA and JC analogous to four of the five mammalian SC domains; however, SC and JC N-terminal extensions, absent in mammals, mediated additional interfaces between complex components. Experiments comparing mammalian and avian SC binding to cognate and non-cognate IgA ligands demonstrated that species-specific structural differences correlated with differences in SC binding and that adding an N-terminal extension to mammalian SC enhanced binding to avian pIgA. Together, results and comparison to published structures indicate that avian IgA components co-evolved unique elements compared to mammalian IgA, including a predominantly tetrameric state, and suggest that birds may employ different IgA effector mechanisms to combat mucosal pathogens compared to mammals. These findings are broadly relevant to understanding IgA evolution and function and combating zoonotic disease such as avian influenza A virus. One Sentence SummaryCryo-electron microscopy structures together with biochemical experiments demonstrate similarities and differences between mammalian and avian secretory immunoglobulin A relevant to understanding differences in immune response to common pathogens such as influenza virus.

immunology↗

bioRxiv2025

Chimeric Immunoglobulin and human Immunoglobulin M structures provide insights on joining-chain independent assembly and function

Polymeric (p) immunoglobulins (Igs) play critical roles in vertebrate immunity. IgM is the evolutionarily oldest pIg and functions both in circulation and in the mucosa. pIgM typically comprises between four and six IgM monomers and up to one joining chain (JC), which in mammals facilitates pIg assembly and promotes delivery to mucosal secretions. Bony fish (teleosts) lack JC and assemble tetrameric IgM whereas humans can express JC-containing pentamers and JC-free hexamers. Here we report cryo-electron microscopy structures of two JC-free chimeric IgM, comprising bony fish and human sequences, and the structure of human hexameric IgM. Chimeric IgM structures adopted unique pentameric geometry distinct from both human and fish pIgM whereas the human hexameric IgM structure adopted hexagonal geometry similar to JC-containing pentameric IgM, albeit with structural differences in center of the molecule. Together results provide new insights on how IgM heavy chain motifs contribute to JC-free pIgM assembly and reveal plasticity of this process, which can be manipulated to create pIg structures not observed in nature. Moreover, we found that antigen-targeting chimeric IgM could neutralize C. difficile toxin cytotoxicity, indicating potential to engineer uniquely structured pIgs to prevent or treat disease.

immunology↗

bioRxiv2023

Structural and biochemical requirements for secretory component interactions with dimeric Immunoglobulin A

Secretory (S) Immunoglobulin (Ig) A is the predominant mucosal antibody that protects host epithelial barriers and promotes microbial homeostasis. SIgA production occurs when plasma cells assemble two copies of monomeric IgA and one joining-chain (JC) to form dimeric (d) IgA, which is bound by the polymeric Ig receptor (pIgR) on the basolateral surface of epithelial cells and transcytosed to the apical surface. There, pIgR is proteolytically cleaved, releasing SIgA, a complex of the dIgA and the pIgR ectodomain, called secretory component (SC). The pIgRs five Ig-like domains (D1-D5) undergo a conformational change upon binding dIgA, ultimately contacting four IgA heavy chains and the JC in SIgA. Here we report structure-based mutational analysis combined with surface plasmon resonance binding assays that identify key residues in mouse SC D1 and D3 that mediate SC binding to dIgA. Residues in D1 CDR3 are likely to initiate binding whereas residues that stabilize the D1-D3 interface are likely to promote the conformation change and stabilize the final SIgA structure. Additionally, we find that the JCs three C-terminal residues play a limited role in dIgA assembly but a significant role in pIgR/SC binding to dIgA. Together results inform new models for the intricate mechanisms underlying IgA transport across epithelia and functions in the mucosa. KEY POINTSO_LIThe secretory component D1 CDR3 loop plays an important role in binding to dIgA. C_LIO_LIThe formation of SC D1-D3 interface stabilizes SIgA. C_LIO_LIJC C-terminal residues influence dIgA assembly and mediate pIgR binding to dIgA. C_LI

immunology↗

bioRxiv2023

Engineered Secretory Immunoglobulin A provides insights on antibody-based effector mechanisms targeting Clostridiodes difficile

Secretory (S) Immunoglobin (Ig) A is the predominant mucosal antibody, which mediates host interactions with commensal and pathogenic microbes, including Clostridioides difficile. SIgA adopts a polymeric IgA structure that is bound by secretory component (SC). Despite significance, how SIgA supports diverse effector mechanisms is poorly characterized and SIgA-based therapies nonexistent. We engineered chimeric (c) SIgAs, in which we replaced SC domain D2 with a single domain antibody or a monomeric fluorescent protein, allowing us to investigate and enhance SIgA effector mechanisms. cSIgAs exhibited increased neutralization potency against C. difficile toxins, promoted bacterial clumping and cell rupture, and decreased cytotoxicity. cSIgA also allowed us to visualize and/or quantify C. difficile morphological changes and clumping events. Results reveal mechanisms by which SIgA combats C. difficile infection, demonstrate that cSIgA design can modulate these mechanisms, and demonstrate cSIgAs adaptability to modifications that might target a broad range of antigens and effector mechanisms.

immunology↗

bioRxiv2023

Suppression of epithelial proliferation and tumorigenesis by immunoglobulin A

Immunoglobulin A (IgA) is the most abundant antibody isotype produced across mammals and plays a specialized role in mucosal homeostasis1. Constantly secreted into the lumen of the intestine, IgA binds commensal microbiota to regulate their colonization and function2,3 with unclear implications for health. IgA deficiency is common in humans but is difficult to study due to its complex aetiology and comorbidities4-8. Using genetically and environmentally controlled mice, here we show that IgA-deficient animals have increased susceptibility to endogenous colorectal tumours. Cellular and molecular analyses revealed that, in the absence of IgA, colonic epithelial cells induce antibacterial factors and accelerate cell cycling in response to the microbiota. Oral treatment with IgA was sufficient to both reduce steady-state proliferation and protect mice from tumours, but this function was due to antibody structure rather than binding specificity. In both organoid and monolayer culture systems, IgA directly suppressed epithelial growth. Co-immunoprecipitation mass spectrometry and a targeted CRISPR screen identified DMBT1 as an IgA-binding epithelial surface protein required for IgA-mediated suppression of proliferation. Together, IgA and DMBT1 regulate Notch signalling and tune the normal cycling of absorptive colonocyte progenitors. In mice, deleting the transmembrane and cytoplasmic signalling portions of DMBT1 or blocking Notch signalling was sufficient to reverse both the increased proliferation and tumour susceptibility of IgA knockouts. These experiments establish a homeostatic function for IgA in tempering physiological epithelial responses to microbiota to maintain mucosal health.

immunology↗

bioRxiv2021

Sequence signatures of two IGHV3-53/3-66 public clonotypes to SARS-CoV-2 receptor binding domain

Since the COVID-19 pandemic onset, the antibody response to SARS-CoV-2 has been extensively characterized. Antibodies to the receptor binding domain (RBD) on the spike protein are frequently encoded by IGHV3-53/3-66 with a short CDR H3. Germline-encoded sequence motifs in CDRs H1 and H2 play a major role, but whether any common motifs are present in CDR H3, which is often critical for binding specificity, have not been elucidated. Here, we identify two public clonotypes of IGHV3-53/3-66 RBD antibodies with a 9-residue CDR H3 that pair with different light chains. Distinct sequence motifs on CDR H3 are present in the two public clonotypes that appear to be related to differential light chain pairing. Additionally, we show that Y58F is a common somatic hypermutation that results in increased binding affinity of IGHV3-53/3-66 RBD antibodies with a short CDR H3. Overall, our results advance fundamental understanding of the antibody response to SARS-CoV-2.

microbiology↗