IgG4 subclass-specific responses to Staphylococcus aureus antigens shed new light on host-pathogen interaction

Abstract

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 alpha-toxin, 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.

FIG 1

IgG1/IgGt and IgG4/IgGt ratios in sera from 40 Algerian volunteers. (A) Median of the IgG1/IgGt ratios in sera from 10 Algerian patients with either joint (dark gray bars), respiratory (light gray bars), or skin (white bars) S. aureus infections and in sera from 10 Algerian control patients without S. aureus infection (black bars). On the x axis, the 40 tested S. aureus antigens are listed. The y axis shows the median IgG1/IgGt signal ratios for each particular antigen. Dotted lines mark 60% (the reported IgG1/IgGt ratio), 30% (50% of this reported value), and 90% (150% of this reported value). (B) Same as for panel A, but showing the IgG4/IgGt ratios. The dotted line marks 5%, which is the reported IgG4/IgGt ratio.

FIG 2

IgG1/IgGt and IgG4/IgGt ratios in sera from 25 Sudanese patients with S. aureus skin infection and 60 healthy Sudanese volunteers. (A) Median of the IgG1/IgGt ratios in sera of 25 Sudanese patients with S. aureus skin infection (white bars) and 60 Sudanese volunteers (black bars). On the x axis, the 38 tested S. aureus antigens are listed (note that SasG and SEB were not included in this particular analysis). The y axis shows the median of the IgG1/IgGt signal ratios for each particular antigen. Dotted lines mark 60% (the reported IgG1/IgGt ratio), 30% (50% of this reported value), and 90% (150% of this reported value). (B) Same as for panel A, but showing the IgG4/IgGt ratios. The dotted line marks 5%, the reported IgG4/IgGt ratio.

FIG 3

IgG1/IgGt and IgG4/IgGt ratios in sera from 10 Dutch bacteremic patients during disease progression. (A) Median of the IgG1/IgGt ratios in 10 Dutch bacteremic patients during disease progression. White bars, IgG1/IgGt ratio at diagnosis. Light gray bars, IgG1/IgGt ratio at 1 week after diagnosis. Dark gray bars, IgG1/IgGt ratio at 2 weeks after diagnosis. Black bars, IgG1/IgGt ratio at 3 weeks after diagnosis. On the x axis, the 17 antigens with increases in either the IgGt, IgG1, or IgG4 signal are depicted. The y axis shows the median of the IgG1/IgGt signal ratios for each particular antigen. The dotted lines mark 60% (the reported IgG1/IgGt ratio), 30% (50% of this reported value), and 90% (150% of this reported value). (B) Same as for panel A, but showing the IgG4/IgGt ratios. The dotted line at 5% marks the reported IgG4/IgGt ratio.

FIG 4

Numbers of S. aureus antigens to which IgG4 responses were detectable in sera from 19 Dutch carriers (circles), 26 Dutch noncarriers (squares), and 13 Dutch EB patients (triangles). Dutch carriers showed a trend to IgG4 serum responses to more antigens than noncarriers (mean of 2.95 and range of 0 to 12 versus mean of 2.68 range of 0 to 11; P = 0.0339). EB patients showed IgG4 responses to significantly more antigens than noncarriers (mean of 5.38 and range of 1 to 11 versus mean of 2.68 and range of 0 to 11; P = 0.0013) and trended toward more IgG4 responses than carriers (mean of 5.38 and range of 1 to 11 versus mean of 2.98 and range of 0 to 12; P = 0.1275). Mean and standard error of the mean (SEM) are plotted.