Transfer of anti-Klebsiella pneumoniae immunity following infection in mice is protective against lethal challenge in offspring

Abstract

Klebsiella pneumoniae is a gram-negative, opportunistic pathogen, with high rates of antimicrobial resistance, and is responsible for a wide range of infections of the urinary tract, lungs, and bloodstream, among others. Disease burden is particularly high in neonates, where K. pneumoniae is a leading cause of sepsis. Renewed interest in vaccine development against this critical priority pathogen has focused on this vulnerable population. Vaccination in pregnancy is a promising approach for prevention of neonatal sepsis, however efforts to understand the dynamics, specificity and function of maternally transferred antibodies is ongoing. We report here that K. pneumoniae-specific IgG is readily transferred from dam to pup following wild-type infection in mice, and that maternally-transferred immunity is protective against lethal infection in pups aged 6 weeks. Further work to investigate the mechanisms of protection and explore neonatal challenge models will advance the path to a maternal vaccine to protect against neonatal sepsis.

Supplementary Information: The online version contains supplementary material available at 10.1038/s41598-025-33619-x.

Fig. 1

Optimization of sub-lethal and lethal infectious doses of K. pneumoniae in mice of both sexes. Mice aged 6 weeks were injected with varying doses of K. pneumoniae by IP injection and monitored for mortality and symptoms of illness. Differences in survival of female (A) and male mice (B) dosing ranges was assessed using Mantel-Cox log-rank tests (n = 6–16, 2 repeats, DF = 1). Groups shown are pooled between different doses that are within 15% of the reported dose. Groups infected with K. pneumoniae were compared with negative control groups; exact p values are denoted. The cumulative symptom score in female (C) and (D) male mice surviving infection. CSS between mice receiving K. pneumoniae (all groups where n > 2) and negative controls were done by Kruskal-Wallis tests with Dunn’s multiple comparison corrections. Exact p-values are reported for all comparisons (DF = 2 female, DF = 2 male). (E) Mice (n = 4 female, n = 6 male) were infected with sub-lethal infectious doses of K. pneumoniae. Anti-K. pneumoniae IgG endpoint titers as determined by ELISA. Negative control mice of both sexes were pooled as all samples were below the lower limit of quantification. Mean log₂ endpoint titers and standard deviation are shown.

Fig. 2

Anti-K. pneumoniae IgG titers are maintained in dams up to 49 days post infection. (A) Female mice aged 6 weeks were injected with 3.9 × 10⁶ CFU of K. pneumoniae by IP injection. Serum was collected from all dams 21 days after infection. Serum was collected from litters and the corresponding dam 1-, 7- and 14-days post birth. Remaining dam serum was collected at weaning, 21 days post birth and approximately 49 days post infection. Weaned pups were challenged with a lethal dose of K. pneumoniae at 42 days old (created in Biorender. https://BioRender.com/k33md8e). (B) Anti-K. pneumoniae IgG endpoint titers in sera collected from dams were determined by ELISA (n = 1–10). Log2 endpoint titers of 10.64 represents titers below the lower limit of quantification. Significant comparisons are shown with lines and p-values from t-tests between the negative control and sub-lethally infected dams at each timepoint. (C) Fold change from baseline titers (pre-infection) were calculated by subtracting the logged baseline endpoint titer from the endpoint titer on the indicated experimental day (n = 1–10). Mean fold change and standard deviation are shown.

Fig. 3

Anti-K. pneumoniae IgG is transferred from dams to pups. (A) Anti-K. pneumoniae IgG endpoint titers in sera collected from pups were determined by ELISA (n = 6–28). 10.64 represents titers below the lower limit of quantification. Titers from pups born of negative control and sub-lethally infected dams at each timepoint were tested by t-test. (B) The ratio of pup/dam anti-K. pneumoniae IgG endpoint titers were calculated by dividing the pup endpoint titer with the endpoint titer of their dam collected at the same time (n = 6–10). (C) The IgG1 over IgG2a ratio was determined by dividing IgG1 endpoint titers by the IgG2a endpoint titer. Dam IgG1/IgG2a ratio 7 days before giving birth are displayed with pup ratios on Day 1, 7, 14 and 42 days after birth (n = 3–8). (D) Dam IgG2a titers 7 days before giving birth are displayed with pup titers on Day 1, 7, 14 and 42 days after birth. Log₂ endpoint titers of 8.64 represents titers below the lower limit of quantification (n = 3–8). Significant comparisons are shown with lines and p-values from a one-way ANOVA with Dunn’s multiple comparison test against dam titers 7 days before giving birth. (E) Dam IgG1 titers 7 days before giving birth are displayed with pup titers on Day 1, 7, 14 and 42 days after birth. Log₂ endpoint titers of 8.64 represents titers below the lower limit of quantification (n = 3–8). A one-way ANOVA detected no significant differences. (F) Pup/dam IgG2a ratios were calculated by dividing the pup endpoint titer with the endpoint titer of their dam collected at the same time (n = 3–7). (G) Pup/dam IgG1 ratios were calculated by dividing the pup endpoint titer with the endpoint titer of their dam collected at the same time (n = 3–7). Box and whiskers plots display minimum and maximum, all other plots show mean and standard deviation. All pup/dam ratio ratios were tested with a Kruskal-Wallis test with Dunn’s multiple comparison test against all pairings (B,F,G). All significant comparisons are displayed with lines and exact p-values.

Fig. 4

Sublethal infection of dams with K. pneumoniae protects pups from lethal challenge at 42 days old. (A) Female (n = 5–8, individual experiment) pup survival following lethal challenge of 6.6 × 10⁶ CFU K. pneumoniae is shown. (B) Male (n = 8–12, two experiments) pup survival following lethal challenge of 3.6 × 10⁶ CFU K. pneumoniae is shown. Survival curves were assessed using Mantel-Cox log-rank tests, exact p values are denoted.