Human Immune Proteome in Experimental Colonization with Staphylococcus aureus |
| |
| Authors: | Silva Holtfreter Thi Thu Hoai Nguyen Heiman Wertheim Leif Steil Harald Kusch Quoc Phong Truong Susanne Engelmann Michael Hecker Uwe V?lker Alex van Belkum Barbara M. Br?ker |
| |
| Affiliation: | Institute of Immunology and Transfusion Medicine,1. Interfaculty Institute of Genetics and Functional Genomics,4. Institute of Microbiology and Molecular Biology, University of Greifswald, Greifswald, Germany,5. Department of Medical Microbiology and Infectious Diseases, University Medical Center, Rotterdam, The Netherlands,2. Oxford University Clinical Research Unit, National Institute of Infectious and Tropical Diseases, Bach Mai Hospital, Hanoi, Vietnam3. |
| |
| Abstract: | More than 20% of adults are persistently colonized with Staphylococcus aureus. When hospitalized, these carriers have increased risks of infection with their own strains. However, a recent study demonstrated a lower incidence of bacteremia-related death among carriers than among noncarriers, raising the question whether the adaptive immune system plays a protective role. In fact, S. aureus carriers mount a highly specific neutralizing antibody response against superantigens of their colonizing strains. We now used 2-dimensional immunoblotting to investigate the profiles of antibodies from healthy individuals against S. aureus extracellular proteins. Moreover, we tested whether symptom-free experimental colonization of these individuals with an S. aureus strain of low virulence, 8325-4, is sufficient to induce an antibody response. Sera obtained before and 4 weeks after colonization were screened for immunoglobulin G (IgG) antibody binding to extracellular staphylococcal proteins. At baseline, most volunteers harbored IgG directed against conserved virulence factors, including alpha-hemolysin (Hla), beta-hemolysin (Hlb), phospholipase C (Plc), staphylococcal serine protease (SspA), and cysteine protease (SspB). However, the variability of spot patterns and intensities was striking and could be important in case of infection. Experimental nasal colonization with S. aureus 8325-4 did not elicit new antibodies or boost the humoral response. Thus, the high antibody prevalence in humans is likely not induced by short-term nasal colonization, and presumably minor infections are required to trigger anti-S. aureus antibody responses.Staphylococcus aureus is one of the most common causes of nosocomial infection, and the species is becoming increasingly resistant to antibiotics (2). Apart from being a major human pathogen, S. aureus is also a frequent colonizer of human skin and mucosa (34). The bacteria find their primary ecological niche in the human nose but are also able to colonize the throat, the intestines, and the perineal region, sometimes exclusively (1, 17). Approximately 20% of the adult population carry S. aureus in the nose persistently, and another 30% carry it intermittently, frequently only for a few days, whereas 50% are noncarriers (NC) (29, 30, 34). Nasal carriers stand an increased risk of developing severe S. aureus infections caused by their autologous strains, especially upon hospitalization or immune suppression (32, 35). This underlines the fact that host and environmental factors play a decisive role in determining the outcome of S. aureus host interactions.In a recent large prospective study, carriers acquired S. aureus bacteremia more frequently than NC but, surprisingly, had a better survival rate than NC (35). This observation raises the question whether the adaptive immune system establishes immunity to the colonizing S. aureus strain, which could be of advantage in autologous infections. In support of this hypothesis, our group recently showed that S. aureus carriers raise a strong and strain-specific antibody response against the superantigen cocktail produced by their colonizing strain (12). However, S. aureus produces a broad repertoire of virulence factors, and the antibody response against superantigens is likely only the tip of an iceberg (8). In fact, anti-S. aureus antibodies against staphylococcal toxins, immune evasion molecules, and adhesins have been detected in healthy individuals as well as in patients (6, 7, 11, 31).Virulence factor expression is strictly regulated in S. aureus. While adhesins are expressed by bacterial cells in logarithmic growth, the majority of known virulence factors, including most superantigens but also cytolytic toxins, proteases, lipases, and several immune evasion molecules, are secreted in the post-exponential-growth phase (23, 38). In contrast to intracellular and cell wall-associated proteins, secreted virulence factors can act systemically while bacteria remain localized. Consequently, these factors are the most likely stimuli of the adaptive immune system during epithelial colonization with S. aureus (28).To date, a comprehensive investigation of anti-S. aureus antibody profiles from healthy individuals and their variability is still lacking. Moreover, it remains unknown which conditions (e.g., nasal colonization, minor or major infections) are required to trigger an antibody response against S. aureus. Therefore, we experimentally colonized the nares of 16 healthy human volunteers with S. aureus (36) and compared the anti-S. aureus antibody profiles before and 28 days after colonization. Our aims were to analyze the variability of the anti-S. aureus antibody profiles and to test whether experimental nasal colonization elicits or boosts an antibody response. |
| |
| Keywords: | |
|
|
