IgG4 Subclass-Specific Responses to Staphylococcus aureus Antigens Shed New Light on Host-Pathogen Interaction

Abstract

f IgG4 responses are considered indicative for long-term or repeated exposure to particular antigens. Therefore, studying IgG4-specific antibody responses against Staphylococcus aureus might generate new insights into the respective host-pathogen interactions and the microbial virulence factors involved. Using a bead-based flow cytometry assay, we determined total IgG (IgGt), IgG1, and IgG4 antibody responses to 40 different S. aureus virulence factors in sera from healthy persistent nasal carriers, healthy persistent noncarriers, and patients with various staphylococcal infections from three distinct countries. IgGt responses were detected against all tested antigens. These were mostly IgG1 responses. In contrast, IgG4 antibodies were detected to alphatoxin, chemotaxis inhibitory protein of S. aureus (CHIPS), exfoliative toxins A and B (ETA and -B), HlgB, IsdA, LukD, -E, -F, and -S, staphylococcal complement inhibitor (SCIN), staphylococcal enterotoxin C (SEC), staphylococcal superantigen-like proteins 1, 3, 5, and 9 (SSL1, -3, -5, and -9), and toxic shock syndrome toxin 1 (TSST-1) only. Large interpatient variability was observed, and the type of infection or geographical location did not reveal conserved patterns of response. As persistent S. aureus carriers trended toward IgG4 responses to a larger number of antigens than persistent noncarriers, we also investigated sera from patients with epidermolysis bullosa (EB), a genetic blistering disease associated with high S. aureus carriage rates. EB patients responded immunologically to significantly more antigens than noncarriers and trended toward even more responses than carriers. Altogether, we conclude that the IgG4 responses against a restricted panel of staphylococcal antigens consisting primarily of immune modulators and particular toxins indicate important roles for these virulence factors in staphylococcal pathogen-host interactions, such as chronicity of colonization and/or (subclinical) infections.

Production of Staphylococcal Complement Inhibitor (SCIN) and Other Immune Modulators during the Early Stages of Staphylococcus aureus Biofilm Formation in a Mammalian Cell Culture Medium

“…Using a competitive Luminex assay and mass spectrometry, we found that during early biofilm formation in the mammalian cell culture medium IMDM, laboratory and clinical strains of S. aureus produced immune modulators, including SCIN and, to a lesser extent, CHIPS and FLIPr. Most of the initially selected immune modulators (based on previous studies showing a relation with S. aureus colonization in vivo [45]) were not produced during the early stages of biofilm formation. This may have been due to the selected culture conditions (medium, surface materials, and timing), which are different from those used in the in vivo situation studied previously (45,47).…”

“…Most of the initially selected immune modulators (based on previous studies showing a relation with S. aureus colonization in vivo [45]) were not produced during the early stages of biofilm formation. This may have been due to the selected culture conditions (medium, surface materials, and timing), which are different from those used in the in vivo situation studied previously (45,47). Nevertheless, our The more immune modulator that was present in the supernatant, the lower the amount of signal that was observed, as the presence of uncaptured specific IgG is inversely related to the presence of the immune modulators in the supernatants.…”

“…Next, 50 l of this mixture was directly used for the simultaneous semiquantification of the noncaptured IgGs specific for S. aureus biofilm-derived immune modulators using Luminex bead-based flow cytometry (Luminex Corporation, Austin, TX, USA). The antigens used in this assay were CHIPS, SCIN, FLIPr, HlgB, LukD, LukE, LukS, SSL1, SSL3, SSL5, SSL9, and SEA (45). All antigens were coupled to MagPlex beads (Luminex Corporation) according to the manufacturer's protocol.…”

“…In a previous study, it was shown that chemotaxis inhibitory protein of staphylococci (CHIPS) and staphylococcal complement inhibitor (SCIN) can be produced during the early stages of planktonic growth of S. aureus and can inhibit chemotaxis and, subsequently, phagocytosis by host immune cells (44). This in combination with the findings of earlier work from our group, in which we observed an increased IgG4 response toward CHIPS, SCIN, formyl peptide receptor-like 1 inhibitor (FLIPr), gamma-hemolysin component B (HlgB), leukocidin D (LukD), LukE, LukS, staphylococcal superantigen-like protein 1 (SSL1), SSL3, SSL5, SSL9, and staphylococcal enterotoxin A (SEA) in the serum of healthy controls and patients suffering from various S. aureus-related infections (45), which made us hypothesize that these virulence factors might be produced by biofilm-associated bacteria. The pathogenic mechanisms of these proteins are described in Table 1.…”

Omics Approaches for the Study of Adaptive Immunity to Staphylococcus aureus and the Selection of Vaccine Candidates

“…Immunoproteomics provides a panoramic view of the intensity and dynamics of antibody binding to S. aureus proteins revealing their immunogenicity [40,158,206,207]. Antibody profiling in patient cohorts by multiplex assays is useful for hypothesis testing as well as for hypothesis generation [133,169,208,209,210]. It leads to the discovery of promising vaccine candidates such as the small set of S. aureus antigens, whose recognition by antibodies was associated with protection from sepsis in S. aureus bacteremia patients [133].…”