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. 2022 Dec 15;9(1):e12071.
doi: 10.1016/j.heliyon.2022.e12071. eCollection 2023 Jan.

Complementary measurement of nontyphoidal Salmonella- specific IgG and IgA antibodies in oral fluid and serum

Sean C Elias  1 , Esther Muthumbi  2   3 , Alfred Mwanzu  2 , Perpetual Wanjiku  2 , Agnes Mutiso  2 , Raphael Simon  4 , Calman A MacLennan  1
Affiliations

Complementary measurement of nontyphoidal Salmonella- specific IgG and IgA antibodies in oral fluid and serum

Sean C Elias et al. Heliyon. .

Abstract

Objectives: Immuno-epidemiological studies of orally acquired, enteric pathogens such as nontyphoidal Salmonella (NTS) often focus on serological measures of immunity, ignoring potentially relevant oral mucosal responses. In this study we sought to assess the levels and detectability of both oral fluid and serum IgG and IgA to NTS antigens, in endemic and non-endemic populations.

Methods: IgG and IgA antibodies specific for Salmonella Typhimurium and Salmonella Enteritidis O antigen and phase 1 flagellin were assessed using Enzyme Linked Immunosorbent Assay (ELISA). Paired oral fluid and serum samples were collected from groups of 50 UK adults, Kenyan adults and Kenyan infants. Additionally, oral fluid alone was collected from 304 Kenyan individuals across a range of ages.

Results: Antigen-specific IgG and IgA was detectable in the oral fluid of both adults and infants. Oral fluid antibody increased with age, peaking in adulthood for both IgG and IgA but a separate peak was also observed for IgA in infants. Oral fluid and serum responses correlated for IgG but not IgA. Despite standardised collection the relationship between oral fluid volume and antibody levels varied with age and country of origin.

Conclusions: Measurement of NTS-specific oral fluid antibody can be used to complement measurement of serum antibody. For IgA in particular, oral fluid may offer insights into how protective immunity to NTS changes as individuals transition with age, from maternal to acquired systemic and mucosal immunity. This may prove useful in helping to guide future vaccine design.

Keywords: Flagellin; IgA; IgG; Nontyphoidal; O-Antigen; Oral fluid.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Oracol+ Saliva Collection Device Instructions for Use. Published with permission - Malvern Medical Developments Ltd, UK.
Figure 2
Figure 2
Differences in level and detectability of antigen specific oral fluid and serum IgG and IgA in UK adults, Kenyan adults and Kenyan infants. O:4,5, O:9, S. Typhimurium (STM) flagellin- and S. Enteritidis (SEN) flagellin-specific oral fluid IgG (A-D) and IgA (E-F) were detected using standardised oral fluid ELISA. O:4,5, O:9, S. Typhimurium (STM) flagellin- and S. Enteritidis (SEN) flagellin-specific serum IgG (I-L) and IgA (M-P) were detected using standardised serum ELISA. ELISA titres reported as antibody units (A.U). Threshold for limit of detection for each assay indicated by dotted red line. Geomean with 95% CI, and P value shown. Also see Table S1. Groups analysis performed using Kruskal-Wallace with Dunns multiple comparison tests. Results shown are for sample dilutions of 1 in 10 for IgG and 1 in 50 for IgA as standard.
Figure 3
Figure 3
Correlations between antigen specific IgG levels in oral fluid and serum UK adults (A-D), Kenyan Adults (E-H) and Kenyan Infants (I-L). Antigens: O:4,5 (row 1), O:9 (row 2), flagellin of Salmonella Typhimurium (STM) (row 3), flagellin of Salmonella Enteritidis (SEN) (row 4). Spearman’s Rank test with r and P values shown. Antibody Units (A.U.).
Figure 4
Figure 4
Correlations between antigen-specific IgA in oral fluid and serum UK adults (A-D), Kenyan Adults (E-H) and Kenyan Infants (I-L). Antigens: O:4,5 (row 1), O:9 (row 2), flagellin of Salmonella Typhimurium (STM) (row 3), flagellin of Salmonella Enteritidis (SEN) (row 4). Spearman’s Rank test with r and P values shown. Antibody Units (A.U.).
Figure 5
Figure 5
Correlations between antigen-specific IgG levels and initial volume of oral fluid collected. UK adults (A-D), Kenyan Adults (E-H) and Kenyan Infants (I-L). Antigens: O:4,5 (row 1), O:9 (row 2), flagellin of Salmonella Typhimurium (STM) (row 3), flagellin of Salmonella Enteritidis (SEN) (row 4). Spearman’s Rank test with r and P values shown. Antibody Units (A.U.).
Figure 6
Figure 6
Correlations between antigen specific IgA levels and initial volumes of oral fluid collected. UK adults (A-D), Kenyan Adults (E-H) and Kenyan Infants (I-L). Antigens: O:4,5 (row 1), O:9 (row 2), flagellin of Salmonella Typhimurium (STM) (row 3), flagellin of Salmonella Enteritidis (SEN) (row 4). Spearman’s Rank test with r and P values shown. Antibody Units (A.U.).
Figure 7
Figure 7
Differences in levels and detectability of antigen-specific oral fluid IgG and IgA with age. Study population was subdivided by age group (Infants: 1–12months, Young Children: 13months-4 years 11 months, Older Children: 5 years -14y 11months, Adults: 15–54 years 11 months, Elderly: 55 years and above). O:4,5 (A-B), O:9 (C-D), S. Typhimurium flagellin (E-F), S. Enteritidis flagellin (G-H). ELISA titres reported as antibody units (A.U). % of individuals with detectable antibody, Geomean with 95% CI shown and P values shown. Also see Table S2. Groups analysed using Kruskal-Wallis with Dunns multiple comparison tests.
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