Total IgA and IgA reactivity to antigen I/II epitopes in HLA-DRB1*04 positive subjects

Abstract

Bacterial adherence to the acquired dental pellicle, important in dental caries (caries), is mediated by receptor-adhesins such as salivary agglutinin binding to Streptococcus mutans antigen I/II (I/II). Ten selected I/II epitopes were chosen to determine their reactivity to human salivary IgA. Previous studies suggested that a specific HLA biomarker group (HLA-DRB1*04) may have differential influence of immune responses to I/II. However, it was not known whether secretory IgA (SIgA) responses to the selected epitopes from HLA-DRB1*04 positive subjects were different compared to controls, or across other caries-related factors such as total IgA (TIgA). Thirty-two total subjects were matched according to HLA type, gender, ethnicity and age. HLA genotyping, oral bacterial, immunoglobulin and antibody analyses were performed. A large observed difference emerged with regard to the natural immune reservoir of TIgA in HLA-DRB1*04 positive subjects, specifically, a 27.6% reduction compared to controls. In contrast to all other epitopes studied, HLA-DRB1*04 positive subjects also exhibited reduced reactivity to I/II epitope 834-853. HLA-DRB1*04 positive subjects exhibited lower specific SIgA activity/TIgA to 834-853 and also a lower specific reactivity to 834-853/whole cell S. mutans UA159. Furthermore, HLA-DRB1*04 positive subjects exhibited lower responses to I/II in its entirety. The large observed difference in TIgA and the 834-853 reactivity pattern across multiple measures suggest potentially important connections pertaining to the link between HLA-DRB1*04 and caries.

Keywords: DRB1; DRB1*04; Dental Caries; HLA-II; I/II; IgA; Immunogenetics; Immunomodulation; Streptococcus mutans.

Figure 1

Schematic and diagramatic representations of the surface protein adhesin, antigen I/II. Antigen I/II is comprised of the following regions (and residues): the signal sequence (1–38), a pre-A region (39–120), the A-region (121–447), V-region (aa 448–839), P-region (840–983), and the C-terminal region (984–1463), and regions for anchor proteins associated with the bacterial cell wall including the LPxTG anchor region (CWA) (1464–1561). The A-region consists of four alanine-rich tandem repeats, specifically A1 (121–201), A2 (202–283), A3 (284–365), and A4 (366–447). The P-region also consists of three to four repeated regions (represented here as four) with about 35 percent proline content, including P1 (840–878), P2 (879–917), P3 (918–956), and P4 (957–983) [26,27].

Figure 2

The log transformed number of S. mutans colony forming units/mL of whole saliva for DRB1*04 positive (n = 16) and negative subjects (n = 16). These data are reported as natural log means and standard errors of the mean.

Figure 3

Human salivary total IgA among HLA-DRB1*04 positive (n = 16) and negative subjects (n = 16).

Figure 4

Human salivary IgA specific activity of HLA-DRB1*04 positive (n = 16) and negative subjects (n = 16) to 10 selected putative epitopes of S. mutans I/II. Specific activity was calculated using the natural log of the ratio of each subject’s SIgA OD reading for each epitope in triplicate to the total IgA OD for each subject. These data are reported in natural log values as means and standard errors of the mean.

Figure 5

Human salivary IgA reactivity ratios of HLA-DRB1*04 positive (n = 16) and negative subjects (n = 16) to 10 selected putative epitopes of S. mutans I/II/S. mutans UA159 whole cells (UA159). These data are reported in natural log values as means and standard errors of the mean.

Figure 6

Human salivary IgA immunoreactivity to the entire I/II antigen on NG8 (indirect measure) in HLA-DRB1*04 positive (n = 16) and negative (n = 16) subjects. Reactivity to NG8 and a I/II-deficient strain (PC3370) was determined and the data were calculated by subtracting OD 490 nm PC3370 values from NG8 values to focus on epitopes of I/II. These data are reported in optical density absorbance (490 nm) as means and standard errors of the mean.