Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2024

Dysregulation in the antibody response to Pseudomonas aeruginosa in people with cystic fibrosis (#46)

Emma L Ledger 1 , Daniel J Smith 2 3 , Joanna B Goldberg 4 , David W Reid 2 3 5 6 , Timothy J Wells 1 5
  1. Frazer Institute, The University of Queensland, Brisbane, Queensland, Australia
  2. Adult Cystic Fibrosis Centre, The Prince Charles Hospital, Brisbane, Queensland, Australia
  3. Northside Clinical Unit, The University of Queensland, Brisbane, Queensland, Australia
  4. Department of Pediatrics, Division of Pulmonary, Asthma, Cystic Fibrosis, and Sleep, Emory University School of Medicine, Atlanta, Georgia, United States of America
  5. Australian Infectious Diseases Research Centre, Brisbane, Queensland, Australia
  6. QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia

Pseudomonas aeruginosa is a multi-drug resistant, opportunistic pathogen which causes chronic pulmonary infections in people with cystic fibrosis (pwCF). Previously, our laboratory discovered a subset of patients with P. aeruginosa lung infections to have high titres of O-antigen specific IgG2 and/or IgA which instead of protecting against infection, inhibited complement-mediated serum killing of infecting strains. These were termed ‘cloaking antibodies’ (cAbs) and were associated with worse lung function in non-CF bronchiectasis and associated with an increased risk of chronic lung allograft dysfunction in lung transplant recipients. More recently, cAbs to P. aeruginosa were identified in the serum of 32% of pwCF, however no correlation to disease was observed. As serum may not be reflective of the lung environment, we aimed to investigate the clinical importance and relevance of cAbs within lung secretions in pwCF.

Here we collected health data, serum, sputum, and isolated infecting P. aeruginosa (128) from 43 pwCF. Serum and sputum were screened for lipopolysaccharide (LPS)-specific antibodies via ELISA, and their ability to kill infecting isolates determined via serum bactericidal assays. We found 30.3% of patients had high titres of LPS-specific IgG2 and/or IgA in their serum that could inhibit complement killing of their cognate bacterial isolate, corroborating previous findings. Interestingly, 11 (84.6%) inhibited isolates were of the O6 O-antigen P. aeruginosa serotype suggesting a structural component important for this mechanism. Only high titres of P. aeruginosa LPS-specific IgA were detected at relevant levels within sputum which directly correlated to titres within serum. As anti-LPS IgG2 did not seem relevant within lung secretions, LPS-specific IgA responses were compared to patient health. We found increased O6 LPS-specific IgA correlated to worse lung function in both serum and sputum. This disease correlation was validated by the addition of a USA cohort of 25 pwCF whom were also largely colonized (52%) with a O6 serotype of P. aeruginosa.

These findings indicate dysregulation in the humoral immune response to P. aeruginosa in pwCF from two geographically distinct locations. We reveal that P. aeruginosa LPS-specific IgA and not IgG2 may play a role in CF pathophysiology and infection persistence warranting further investigation.