IgG Binds Escherichia coli Serine Protease EspP and Protects Mice From E. coli O157:H7 Infection Ashmita Tontanahal 1 , Vanessa Sperandio 2 , Olga Kovbasnjuk 3 , Sebastian Loos 1 , Ann-Charlotte Kristoffersson 1 , Diana Karpman 1 * and Ida Arvidsson 1 1 Department of Pediatrics, Clinical Sciences Lund, Lund University, Lund, Sweden, 2 Departments of Microbiology and Biochemistry, University of Texas Southwestern Medical Center, Dallas, TX, United States, 3 Division of Gastroenterology, Department of Internal Medicine, University of New Mexico Health Science Center, Albuquerque, NM, United States Shiga toxin-producing Escherichia coli O157:H7 is a virulent strain causing severe gastrointestinal infection, hemolytic uremic syndrome and death. To date there are no specific therapies to reduce progression of disease. Here we investigated the effect of pooled immunoglobulins (IgG) on the course of disease in a mouse model of intragastric E. coli O157:H7 inoculation. Intraperitoneal administration of murine IgG on day 3, or both on day 3 and 6, post-inoculation improved survival and decreased intestinal and renal pathology. When given on both day 3 and 6 post-inoculation IgG treatment also improved kidney function in infected mice. Murine and human commercially available IgG preparations bound to proteins in culture filtrates from E. coli O157:H7. Bound proteins were extracted from membranes and peptide sequences were identified by mass spectrometry. The findings showed that murine and human IgG bound to E. coli extracellular serine protease P (EspP) in the culture filtrate, via the IgG Fc domain. These results were confirmed using purified recombinant EspP and comparing culture filtrates from the wild-type E. coli O157:H7 strain to a deletion mutant lacking espP. Culture filtrates from wild-type E. coli O157:H7 exhibited enzymatic activity, specifically associated with the presence of EspP and demonstrated as pepsin cleavage, which was reduced in the presence of murine and human IgG. EspP is a virulence factor previously shown to promote colonic cell injury and the uptake of Shiga toxin by intestinal cells. The results presented here suggest that IgG binds to EspP, blocks its enzymatic activity, and protects the host from E. coli O157:H7 infection, even when given post-inoculation. Keywords: Escherichia coli O157:H7, Shiga toxin, EspP, immunoglobulin G, hemolytic uremic syndrome, mouse INTRODUCTION Enterohemorrhagic Escherichia coli (EHEC) is a human pathogen, transmitted via contaminated food and water causing diarrhea and hemorrhagic colitis. It is the main cause of hemolytic uremic syndrome (HUS) (1). EHEC is a non-invasive bacterium (2) that exerts its effects by the release of virulence factors such as Shiga toxin (3, 4). The most common clinical isolate is E. coli O157:H7 (5). Upon ingestion, EHEC is transported to the large intestine where it colonizes the gut by intimate Frontiers in Immunology | www.frontiersin.org February 2022 | Volume 13 | Article 807959 1 Edited by: Joseph Alex Duncan, University of North Carolina at Chapel Hill, United States Reviewed by: John Bernet Johnson, Rajiv Gandhi Centre for Biotechnology, India Roberto Mauricio Vidal, University of Chile, Chile Juan C. Salazar, University of Chile, Chile *Correspondence: Diana Karpman diana.karpman@med.lu.se Specialty section: This article was submitted to Microbial Immunology, a section of the journal Frontiers in Immunology Received: 02 November 2021 Accepted: 31 January 2022 Published: 18 February 2022 Citation: Tontanahal A, Sperandio V, Kovbasnjuk O, Loos S, Kristoffersson A-C, Karpman D and Arvidsson I (2022) IgG Binds Escherichia coli Serine Protease EspP and Protects Mice From E. coli O157:H7 Infection. Front. Immunol. 13:807959. doi: 10.3389/fimmu.2022.807959 ORIGINAL RESEARCH published: 18 February 2022 doi: 10.3389/fimmu.2022.807959