Proteomic Identification of OprL as a Seromarker for Initial Diagnosis of Pseudomonas aeruginosa Infection of Patients with Cystic Fibrosis

Identification of new immunogenic antigens that diagnose initial Pseudomonas aeruginosa infections in patients with cystic fibrosis (CF) alone or as an adjunct to microbiology is needed. In the present study, a proteomic analysis was performed to obtain a global assessment of the host immune response during the initial P. aeruginosa infection of patients with CF. Matrix-assisted laser desorption ionization-time of flight mass spectrometry was used to identify outer membrane protein L (OprL), a non-type III secretion system (TTSS) protein, as an early immunogenic protein during the initial P. aeruginosa infection of patients with CF. Longitudinal Western blot analysis of sera from 12 of 14 patients with CF detected antibodies to OprL during the initial P. aeruginosa infection. In addition, also detected were antibodies to ExoS, ExoU, or ExoS and ExoU, the latter indicating sequential P. aeruginosa infections during initial infections. Detection of serum reactivity to OprL, along with proteins of the TTSS, and in conjunction with microbiology may diagnose initial P. aeruginosa infections in patients with CF.Cystic fibrosis (CF) is an autosomal recessive multisystem disease which is caused by mutations in the CF transmembrane conductance receptor. Patients with CF have chronic respiratory infections which are the primary cause of morbidity and premature mortality (16). Patients with CF are infected with bacterial pathogens on an age-dependent timeline (16). Typically, Staphylococcus aureus and nonencapsulated Haemophilus influenzae are the first isolates from infants with CF (34, 35). However, Pseudomonas aeruginosa infections in children with CF are associated with progressive lung disease (30, 33). Microbiology is used for the diagnosis of P. aeruginosa, but successful P. aeruginosa isolation can be complicated in nonexpectorating populations of infants and young children with CF (4). The diagnosis and eradication of the initial P. aeruginosa infection with antibiotics to prevent chronic infection and mucoid transformation are important, since this diagnosis influences the quality of life and long-term patient survival (1, 2, 7, 11, 29, 30). Non-culture-based tests, like serology, should assist microbiology in the early diagnosis of P. aeruginosa infection.P. aeruginosa serology continues to be challenging without defined commercially available antigens licensed in the United States that reflect the molecular pathogenesis of P. aeruginosa upon adaptation to the host environment (13). Høiby (24) and Döring and Høiby (10) have detected an antibody response against a pool of antigens from common P. aeruginosa serotypes. Elevating antibody titers against this pool of antigens correlated with worsening P. aeruginosa infections and a poor clinical prognosis. The clinical progression of CF lung disease may be a reflection of the molecular pathogenesis of P. aeruginosa. Recent studies have correlated serological reactivity and known P. aeruginosa virulence factors. West et al. (42) showed that during the initial P. aeruginosa infection of children with CF, detection of serum antibodies to exotoxin A (ETA) and a P. aeruginosa lysate occurred earlier than detection of serum antibodies to elastase or alkaline phosphatase; subsequently, Corech et al. (6) detected antibodies to components of the type III secretion system (TTSS) at a time similar to that of P. aeruginosa Sup and earlier than ETA, showing the potential of measuring the antibody response to components of the TTSS as an indication of initial infection with P. aeruginosa in children with CF. This also indicated a role for TTSS in the initial P. aeruginosa pathogenesis of the CF lung.In the present study, a proteomic analysis was performed to obtain a global assessment of the host immune response during the initial P. aeruginosa infection of patients with CF. The goal was to identify a cellular component of P. aeruginosa that elicits an early immune response to P. aeruginosa infection to provide a stable immunogenic indication of P. aeruginosa infection relative to P. aeruginosa virulence factors that may fluctuate in expression during the course of P. aeruginosa infection, especially following transition from the acute to the chronic infection phase (41). Outer membrane protein L (OprL), a non-TTSS protein, was identified as an early immunogenic protein in the initial P. aeruginosa infection of patients with CF.