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Lyme disease is a tick-borne, multisystem infection caused by the spirochete Borreliella burgdorferi. Although Abs have been implicated in the resolution of Lyme disease, the specific B cell epitopes targeted during human infections remain largely unknown. In this study, we characterized and defined the structural epitope of a patient-derived bactericidal monoclonal IgG (B11) against outer surface protein C (OspC), a homodimeric lipoprotein necessary for B. burgdorferi tick-mediated transmission and early-stage colonization of vertebrate hosts. High-resolution epitope mapping was accomplished through hydrogen deuterium exchange-mass spectrometry and X-ray crystallography. Structural analysis of B11 Fab-OspCA complexes revealed the B11 Fabs associated in a 1:1 stoichiometry with the lateral faces of OspCA homodimers such that the Abs are essentially positioned perpendicular to the spirochete's outer surface. B11's primary contacts reside within the membrane-proximal regions of α-helices 1 and 6 and adjacent loops 5 and 6 in one OspCA monomer. In addition, B11 spans the OspCA dimer interface, engaging opposing α-helix 1', α-helix 2', and loop 2-3' in the second OspCA monomer. The B11-OspCA structure is reminiscent of the recently solved mouse transmission blocking monoclonal IgG B5 in complex with OspCA, indicating a mode of engagement with OspC that is conserved across species. In conclusion, we provide a detailed insight into the interaction between a functional human Ab and an immunodominant Lyme disease Ag long considered an important vaccine candidate., (Copyright © 2024 by The American Association of Immunologists, Inc.)

319-44 is a human monoclonal antibody capable of passively protecting mice against tick-mediated infection with Borreliella burgdorferi, the bacterial genospecies responsible for Lyme disease in North America. In vitro, 319-44 has complement-dependent borreliacidal activity and spirochete agglutinating properties. Here, we report the 2.2 Å-resolution crystal structure of 319-44 Fab fragments in complex with Outer surface protein A (OspA), the ~30 kDa lipoprotein that was the basis of the first-generation Lyme disease vaccine approved in the United States. The 319-44 epitope is focused on OspA β-strands 19, 20, and 21, and the loops between β-strands 16-17, 18-19, and 20-21. Contact with loop 20-21 explains competition with LA-2, the murine monoclonal antibody used to estimate serum borreliacidal activities in the first-generation Lyme disease vaccine clinical trials. A high-resolution B-cell epitope map of OspA will accelerate structure-based design of second generation OspA-based vaccines., (© 2023 Wiley Periodicals LLC.)

Following an episode of cholera, a rapidly dehydrating, watery diarrhea caused by the Gram-negative bacterium, Vibrio cholerae O1, humans mount a robust anti-lipopolysaccharide (LPS) antibody response that is associated with immunity to subsequent re-infection. In neonatal mouse and rabbit models of cholera, passively administered anti-LPS polyclonal and monoclonal (MAb) antibodies reduce V. cholerae colonization of the intestinal epithelia by inhibiting bacterial motility and promoting vibrio agglutination. Here we demonstrate that human anti-LPS IgG MAbs also arrest V. cholerae motility and induce bacterial paralysis. A subset of those MAbs also triggered V. cholerae to secrete an extracellular matrix (ECM). To identify changes in gene expression that accompany antibody exposure and that may account for motility arrest and ECM production, we subjected V. cholerae O1 El Tor to RNA-seq analysis after treatment with ZAC-3 IgG, a high affinity MAb directed against the core/lipid A region of LPS. We identified > 160 genes whose expression was altered following ZAC-3 IgG treatment, although canonical outer membrane stress regulons were not among them. ompS (VCA1028), a porin associated with virulence and indirectly regulated by ToxT, and norR (VCA0182), a σ54-dependent transcription factor involved in late stages of infection, were two upregulated genes worth noting., (© FEMS 2020.)

Non-typhoidal Salmonella enterica strains, including serovar Typhimurium (STm), are an emerging cause of invasive disease among children and the immunocompromised, especially in regions of sub-Saharan Africa. STm invades the intestinal mucosa through Peyer's patch tissues before disseminating systemically. While vaccine development efforts are ongoing, the emergence of multidrug resistant strains of STm affirms the need to seek alternative strategies to protect high-risk individuals from infection. In this report, we investigated the potential of an orally administered O5 serotype-specific IgA monoclonal antibody (mAb), called Sal4, to prevent infection of invasive Salmonella enterica serovar Typhimurium (STm) in mice. Sal4 IgA was delivered to mice prior to or concurrently with STm challenge. Infectivity was measured as bacterial burden in Peyer's patch tissues one day after challenge. Using this model, we defined the minimal amount of Sal4 IgA required to significantly reduce STm uptake into Peyer's patches. The relative efficacy of Sal4 in dimeric and secretory IgA (SIgA) forms was compared. To assess the role of isotype in oral passive immunization, we engineered a recombinant IgG1 mAb carrying the Sal4 variable regions and evaluated its ability to block invasion of STm into epithelial cells in vitro and Peyer's patch tissues. Our results demonstrate the potential of orally administered monoclonal IgA and SIgA, but not IgG, to passively immunize against invasive Salmonella. Nonetheless, the prophylactic window of IgA/SIgA in the mouse was on the order of minutes, underscoring the need to develop formulations to protect mAbs in the gastric environment and to permit sustained release in the small intestine., Competing Interests: AR, JD, SL, GW, and NM declare that no competing interests exist. MP, KW, and LZ are employees of MappBio, Inc.