Humoral immune responses to microbial polysaccharide surface antigens can prevent bacterial infection but are typically strain specific and fail to mediate broad protection against different serotypes. Here we describe a panel of affinity-matured monoclonal human antibodies from peripheral blood immunoglobulin M–positive (IgM+) and IgA+ memory B cells and clonally related intestinal plasmablasts, directed against the lipopolysaccharide (LPS) O-antigen of Klebsiella pneumoniae, an opportunistic pathogen and major cause of antibiotic-resistant nosocomial infections. The antibodies showed distinct patterns of in vivo cross-specificity and protection against different clinically relevant K. pneumoniae serotypes. However, cross-specificity was not limited to K. pneumoniae, as K. pneumoniae–specific antibodies recognized diverse intestinal microbes and neutralized not only K. pneumoniae LPS but also non–K. pneumoniae LPS. Our data suggest that the recognition of minimal glycan epitopes abundantly expressed on microbial surfaces might serve as an efficient humoral immunological mechanism to control invading pathogens and the large diversity of the human microbiota with a limited set of cross-specific antibodies.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
We thank S. Kaluzewski (National Institute of Public Health–National Institute of Hygiene) for an unencapsulated mutant of a prototype O3:K55 strain 5505; S. Melegh (University of Pécs) for clinical isolates Kp2 (O3:K60) and Kp14 (O3:K35); A. Valverde (University Hospital Ramón y Cajal) for clinical isolate Kp81 (O3b:K non-typeable); A. Heidtmann, L. Kummer, B. Jocher and J. Braun for help with sample acquisition; C. Varga for performing animal experiments; C. Busse for help with experimental design; M. Nussenzweig (The Rockefeller University) for recombinant gp140 from strain YU2; and P. Sehr, R. Murugan, P. Thiele, C. Winter, D. Foster, A. Götze and the DKFZ High-Throughput Sequencing Unit of the Genomics and Proteomics Core Facility and the DKFZ and MPIIB Flow Cytometry Core Facilities for technical support. Supported by the European Funding Program Eurostars (E! 7563 – KLEBSICURE), powered by EUREKA and the European Community; the German Federal Ministry of Education and Research (H.W.); and the International Max Planck Research School for Infectious Diseases and Immunology (T.R.).
Integrated supplementary information
a, Schematic linear structure of biotinylated O3 K. pneumoniae O-antigen; repeating unit (outlined), MeP = Methylphosphate; Man = Mannose; KdO = 3-Deoxy-D-manno-oct-2-ulosonic acid; GlcNAc = N-acetylglucosamine; Hep = L-glycero-D-manno-heptose; PEG = Polyethylene glycol. b, Percentage of O3-reactive 7-AAD−, CD19+, CD27+ peripheral blood B cells in eight donors compared to the background staining using non-biotinylated O3 (right). p-value was calculated using two-tailed Student’s t-test. Data are representative of at least two independent experiments.
a, IGH gene isotype distribution for O3-reactive PB memory B cells isolated by flow cytometric single cell sorting. b,c, IGHV gene family usage for O3-reactive PB memory B cells of the indicated isotypes from the same donors as shown in panel a (b) and LP plasmablasts isolated by flow cytometric single cell sorting from the indicated donors (c). d, Percentage of mutated and unmutated IGHV genes from O3-reactive PB memory B cells of the same donors as in panel a. e, Distribution of cell clusters of clonally related (gray boxes) compared to unique non-related (white) O3-reactive B cells in PB memory B cells or LP plasmablasts from the indicated donors. f, Clonal relationship of O3-reactive B cells of the indicated isotypes in PB memory B cells and LP plasmablasts of donors HD02, HD05, and HD10. Colors depict individual B cell clusters. n indicates numbers of analyzed sequences.
Supplementary Figure 3 O3-reactive PB memory B cell and LP plasmablast antibodies bind specifically to O3 O-antigen.
a, Immunoblot with whole O3 LPS for representative mAbs cloned from O3-reactive memory B cells from PB (036, 286) and from LP plasmablasts (601). b, O3 and streptavidin reactivity of individual recombinant mAbs from O3-reactive PB memory B cells (n = 41) and LP plasmablasts (n = 41) based on ELISA area under curve (AUC) measurements. c, Insulin ELISA reactivity of O3-reactive PB memory B cell antibodies (n = 41) under blocking conditions with 2% BSA. d, Polyreactivity ELISA with E. coli LPS, dsDNA and insulin under non-blocking conditions without BSA. Representative mAbs compared to the positive and negative control mAbs are shown. Dashed lines in indicate negative thresholds (b-d). Data are representative data of at least two independent experiments (a-d).
Gene sequence alignment of IGH and IGK or IGL variable regions of the indicated mutated mAbs and their inferred germline counterpart compared to the respective germline V and J gene segments. CDRs are highlighted.
a, mAb 703 shows specificity for O5 in immunoblot with whole LPS. b, Reactivity of mAb 703 with intestinal murine microbes as measured by flow cytometry. Sorting gate and percentage of antibody-bound bacteria is indicated. Boxes show the K. pneumoniae O-serotype, S. cerevisiae, and gp140 reactivity profile (strong-black; non-reactive-white). Data are representative of two independent experiments.
Supplementary Figure 6 Immunoglobulin gene features and antibody characteristics of O1-reactive PB B cells.
a, Schematic linear structure of biotinylated O1; repeating units (outlined); Gal = Galactose; KdO = 3-Deoxy-D-manno-oct-2-ulosonic acid; GlcNAc = N-acetylglucosamine; Hep = L-glycero-D-manno-heptose; PEG = Polyethylene glycol. b, Flow cytometric analysis of the frequency of 7-AAD−, CD19+ PB B cells reactive to biotinylated O1 (right) compared to the negative control using non-biotinylated O1 (left) for a representative healthy donor detected by Streptavidin Alexa647 conjugate. Gates and percentages indicate the frequency of O1-reactive cells. c, Percentage of O1-reactive 7-AAD−, CD19+ PB B cells (left) in eight donors compared to the background staining using non-biotinylated O1 (right). p-value was calculated using two-tailed Student’s t-test. d, IGH gene isotype usage for O1-reactive PB memory B cells from the same donors as in panel c. Means (red lines) and SD (black lines) are indicated. e, IGHV gene family usage for O1-reactive PB memory B cells of the indicated isotypes from the same donors as shown in panel d. n represents the number of analyzed IGH sequences per isotype. f, Percent of clonally-related O1-reactive B cells per sample in PB memory B cells of the same donors as in panel d. Means (red lines) and SD (black lines) are indicated. g, Number of somatic hypermutations in IGHV genes of the indicated isotypes from O1-reactive peripheral blood B cells. Data are pooled from the same eight donors as in panel d. Means (red lines) and SD (black lines) are indicated. n represents the number of analyzed IGH sequences per isotype. h, Percentage of mutated and unmutated IGHV genes from O1-reactive PB memory B cells. i, O1-reactivity of mAbs cloned from O1-reactive PB memory B cells as measured by ELISA. Green lines indicate the negative isotype control mAb and red lines the threshold for positivity. n indicates the number of tested mAbs. j, Immunoblot reactivity with O1, O2, and O3 LPS for a representative O1-reactive (anti-galactan II) mAb; + and - indicate serotypes expressing the galactan III or the galactan I variant, respectively. k, O1 and streptavidin reactivity of individual mAbs from O1-reactive PB memory B cells based on ELISA area under curve (AUC) measurements. l, IGHV gene somatic hypermutation counts for ELISA O1-specific mAbs (i, k) of the indicated isotypes (IGHM, n = 3; IGHA, n = 3). Red lines indicate means. m, Anti-O1 ELISA reactivity of the indicated mAb (top) and its predicted germline form (bottom). Green lines indicate reactivity of the negative isotype control mAb. Red lines indicate negative thresholds. n, Reactivity of the O1-reactive mAb 196 with murine intestinal microbes as measured by flow cytometry (Fig. 6a). Sorting gate and percentage of antibody-bound bacteria is indicated. Boxes show the K. pneumoniae O-serotype, S. cerevisiae, and gp140 reactivity profile (non-reactive-white). Red diagonal lines indicate non-tested. Data are representative of at least two independent experiments (b, c, i – k, m, n).
Supplementary Figure 7 Cross-specificity of individual K. pneumoniae O-antigen reactive antibodies with microbes from human intestine.
a,b, Reactivity of the indicated mAbs with intestinal microbes of 31/41 tested human stool samples (a) and from a single individual as measured by flow cytometry compared to the PBS negative control (b). Sorting gate and percentage of antibody-bound bacteria are indicated. The K. pneumoniae O-serotype, S. cerevisiae, and gp140 reactivity profiles of each antibody are shown. Data are representative of two independent experiments (b).