Fig. 3: Antibodies to KP O1 O-antigen protect against KP pulmonary challenge.

Mice that had cleared pre-infection with CR_WT and CR_KPO1+pespO were challenged by intratracheal infection with 500 CFU of KP_WT. At 72 hpi we analysed KP replication (A, B) and host-derived severity indicators (C–O). n = 15 mice per group (starting) over 3 biological repeats. A, B KP_WT replication and bacteraemia are significantly reduced in the lungs (A) and blood (B) of CR_KPO1+pespO-preinfected mice compared to CR_WT controls. Central tendency: median. Two-sided Mann–Whitney test. C KP_WT induces significant weight loss in CR_WT-preinfected mice, which is reversed in CR_KPO1+pespO preinfection. Central tendency: mean, error: standard deviation (SD). Two-sided Mann–Whitney test. D–F Clinical haematological markers of disease severity are significantly improved in CR_KPO1+pespO -preinfected mice compared to CR_WT controls. Total white cell counts (D), lymphocyte counts (E) and platelets counts (F) are significantly lower in CR_WT-preinfected controls, indicating increased diseases severity. The innate responders, neutrophils (G) are unchanged between the CR_WT and CR_KPO1+pespO preinfected groups. Central tendency: mean, error: SD. Two-sided unpaired T-test. H–J. The acute phase reactants (Serum amyloid A (H), C-reactive protein (I) and Albumin (J)) demonstrate a reduced inflammatory state in CR_KPO1+pespO -preinfected mice compared to CR_WT controls. Central tendency: mean, error: SD. H and J Two-sided Mann–Whitney test, I Unpaired T-test. K–M Acute lung injury markers (lung homogenate IL1β (K), serum surfactant protein D (L) and lung homogenate myeloperoxidase (M)) are improved by pre-infection with CR_KPO1+pespO compared to CR_WT preinfection. Significant reductions in lung IL1β, improvement in the alveolar capillary barrier (surfactant protein D) and neutrophilic alveolitis (myeloperoxidase) indicate α-KP O1 Abs protect against lung injury. Central tendency: mean, error: SD. K and M Two-sided Mann–Whitney test, L Two-sided unpaired t-test. N, O Acute kidney injury and excretory renal failure are reduced in mice preinfected with CR_KPO1+pespO compared to CR_WT. Serum creatinine (N) and serum cystatin C (O) are reduced in KP_WT infected mice who have cleared preinfection with CR_KPO1+pespO compared to CR_WT. Central tendency: mean, error: SD. Two-sided unpaired t-test. ns non-significant; *, p < 0.5 **; p < 0.01, ***, p < 0.001; ****, p < 0.0001. Source data and exact p-values are provided in the Source Data file.