Assessment of Age-Related Changes of Salivary Immunoglobulin A Levels among Healthy Individuals.

BACKGROUND: Secretory immunoglobulin A (IgA) is the first line of defense against pathogens that invade mucosal surfaces. It has been reported that the immune system exhibits profound age-related changes. The aim of this study was to investigate the age-dependent changes of salivary IgA among healthy individuals.
MATERIALS AND METHODS: Saliva samples were collected from 120 healthy individuals (aged 11-70 years). The salivary IgA concentrations were measured by the use of a single radial immunodiffusion technique and analyzed using the Mann-Whitney U, Kruskal-Wallis, and Chi-square tests.
RESULTS: The mean salivary IgA levels were 81.11 ± 4.50 mg/dl at age 11-20 years, 92.71 ± 13.76 mg/dl at age 21-30 years, 96.50 ± 4.04 mg/dl at age 31-40 years, 104.96 ± 10.15 mg/dl at age 41-50 years, 113.22 ± 7.85 mg/dl at age 51-60 years, and 91.38 ± 4.77 mg/dl at age 61-70 years. There was a significant difference among the mean salivary IgA levels of different age groups (P < 0.001).
CONCLUSION: These results showed that the salivary IgA levels exhibit age-related changes. Oral immunization may be considered to improve oral immunity when the salivary concentrations of IgA begin to decrease during lifetime. Copyright:

INTRODUCTION

S ecretory immunoglobulin A (IgA) constitutes the predominant immunoglobulin isotype in secretions, including saliva. It is considered to be the first line of defense of the host against pathogens that colonize or invade mucosal surfaces.[1] Salivary IgA antibodies could help maintain the integrity of the oral surfaces by preventing microbial adherence to epithelial and tooth surfaces, by neutralizing enzymes, toxins, and viruses, or by acting in synergy with other antibacterial factors such as lysozyme, lactoferrin, salivary peroxidase, and mucins.[12] Salivary IgA may also prevent the penetration of food antigens in the oral mucosa. Some studies have also demonstrated that a lower incidence of caries resulted from a high salivary IgA concentration.[34] In addition, a lower concentration of IgA in saliva has been presented as a risk factor for upper respiratory infection in children and the elderly.[5] Furthermore, lower levels of salivary IgA are associated with increased risk for periodontal disease and caries.[67]

However, it has been shown that mucosal immunization is an effective method in increasing the IgA levels in mucosal secretions.[8] Accordingly, it may be possible to induce salivary IgA response via oral immunization, when the salivary IgA concentrations begin to decrease during a lifetime. This strategy could help the maintenance of the salivary IgA levels and improve the oral immunity.

MATERIALS AND METHODS

The study included 120 healthy individuals visiting the Department of Oral Medicine and Radiology for routine dental health checkups at Vasantdada Patil Dental College and Hospital, Sangli, in various study groups. The study groups were categorized into six different groups – Group I: 11–20 years, Group II: 21–30 years, Group III: 31–40 years, Group IV: 41–50 years, Group V: 51–60 years, and Group VI: 61–70 years. The entire project was submitted to the Ethical Committee of our institute, and the approval was obtained for the study. Informed consent was obtained from parents of school-going children (minor group), and the patients willing to participate in the study were enrolled.

Inclusion criteria

Only healthy individuals in the second to seventh decade of their life.

Exclusion criteria

Patients with history of any pathology associated with oral mucosa

Patients with history of salivary gland disorders

Patients with history of tobacco and alcohol consumption

Patients with history of systemic illness.

Collection of saliva

The saliva samples were collected between 10 and 11 am. Patients were instructed not to eat or drink for at least before the collection of saliva samples. The patient was asked to sit idle for 5 min and to collect saliva. For saliva collection, participants were asked to generate saliva in their mouths and to spit into sterilized wide containers. The saliva samples were stored in a refrigerator and then transported to the laboratory. In the laboratory, all samples were then centrifuged to 15 min at 1000 rpm to remove cells and debris.

Estimation of salivary immunoglobulin

The quantitative estimation of immunoglobulin IgA was done by a single radial immune diffusion technique.[9] This method consists of radial diffusion of salivary antigen from point application into the antibody-containing gels forming a circular precipitate at the point of equivalence.

Statistical analysis

Differences in variables were analyzed using the Mann–Whitney U, Kruskal-Wallis, and Chi-square tests as appropriate, and P < 0.05 was considered statistically significant.

RESULTS

According to our study, the results of salivary IgA levels in different age groups were as follows: Group 1 (11–20 years) showed values of 81.11 ± 4.50 mg/dl, Group 2 (21–30 years) showed 92.71 ± 13.76 mg/dl, Group 3 (31–40 years) showed 96.50 ± 4.04 mg/dl, Group 4 (41–50 years) showed 104.96 ± 10.15 mg/dl, Group 5 (51–60 years) showed 113.22 ± 7.85 mg/dl, and Group 6 (61–70 years) showed 91.38 ± 4.77 mg/dl [Table 1]. Statistical analysis showed a significant difference among mean salivary IgA levels of different age groups (P < 0.001). These results showed that the mean salivary IgA level increased with increasing age up to 60 years and then decreased in the last age group, i.e., from 61 to 70 years [Graph 1]. Alterations in pattern of salivary IgA were observed in the male and female groups. In each age group, the mean salivary IgA levels tended to be slightly higher in women, although the differences were not statistically significant [Table 2].

Table 1

Comparison of six age groups with respect to IgA levels by Kruskal-Wallis ANOVA

Age groups (years)	Means±SD	Median	Mean rank
11-20	81.11±14.50	79.38	28.60
21-30	92.71±13.76	93.27	49.10
31-40	96.50±4.04	96.51	58.95
41-50	104.96±10.15	101.71	83.42
51-60	113.22±7.85	112.44	101.80
61-70	91.38±4.77	90.53	41.12
H		62.0930
P		0.00001*

*P value of the study is = 0.00001. SD: Standard deviation

Graph 1

Comparison of six age groups with respect to immunoglobulin A levels

Table 2

Comparison of males and females in six age groups with respect to IgA levels by Mann-Whitney U test

Variable (years)	Sex	Mean±SD	Median	Mean rank	U	Z	P
11-20	Male	77.01±16.30	72.91	8.70	32.00	-1.3607	0.1736
	Female	85.21±11.87	80.04	12.30
21-30	Male	87.03±12.91	83.31	8.00	25.00	-1.8898	0.0588
	Female	98.38±12.71	96.86	13.00
31-40	Male	95.48±4.01	95.99	8.90	34.00	-1.2095	0.2265
	Female	97.52±4.00	97.91	12.10
41-50	Male	103.96±12.61	100.80	9.80	43.00	-0.5292	0.5967
	Female	105.95±7.50	102.91	11.20
51-60	Male	111.68±9.37	111.45	9.40	39.00	-0.8315	0.4057
	Female	114.76±6.08	113.02	11.60
61-70	Male	91.66±5.05	91.82	10.90	46.00	-0.3024	0.7624
	Female	91.09±4.72	90.36	10.10

SD: Standard deviation

DISCUSSION

Secretory IgA is considered to be the principal mediator of host defense at mucosal surfaces.[1] We hereby described the changes of salivary IgA and IgE levels across different ages from 1 to 70 years. As we observed, the salivary IgA levels increased with increasing age up to 60 years and then decreased. Moreover, the detectable rates and levels of salivary IgA increased from age 1 to 40 years and then decreased. The salivary concentrations of both immunoglobulins were higher in adults compared to children. In some studies, the age-related changes of salivary immunoglobulin concentrations (especially IgA) have been reported. Eliasson et al.[10] investigated the IgA concentrations in secretions of palatal, buccal, and labial salivary glands in individuals aged 18–72 years. They have observed that the salivary IgA concentrations in these saliva samples were higher in elderly individuals (≥65 years) as compared to individuals aged 18–64 years. Increased whole-saliva IgA concentrations in older ages have been attributed partly to positive age-related effects on IgA concentration in the buccal gland secretion. Weemaes et al.[11] reported that the salivary IgA secretion rate increased during infancy and childhood period at age 1–12 years. Childers et al.[12] determined the concentration of IgA in parotid saliva of healthy children (age 6–12 years, n = 14) and healthy adults (age 22–51 years, n = 20) and reported that the levels of IgA increased with age. Challacombe et al.[13] showed in healthy adults that the salivary IgA concentrations increased with age and reached the maximum levels in the oldest studied group (>80 years). These investigations are nearly consistent with our results. However, genetic and environmental differences and differential oral health may account for some different results obtained in this study and those reported by other investigators. For example, in our study, the mean salivary IgA levels decreased after 60 years. Our results regarding decline in salivary IgA concentration after 60 years may be attributed to the increased susceptibility of elderly individuals to oral infectious diseases, especially infection with IgA-degrading bacteria.[1] Regarding salivary IgA changes, it has been reported that the stimulus for IgA synthesis at mucosal surfaces appears to be the colonization of these surfaces by commensal bacteria-bearing polyclonal mitogens such as lipopolysaccharide and perhaps lipoteichoic acid, since germ-free mammals have underdeveloped mucosa-associated lymphoid tissues and lack IgA in their secretions.[1415] Although IgA is thought to act to exclude extrinsic pathogenic microorganisms, it appears to be without effect on commensal bacteria, since these microbes colonize and persist on mucosal and tooth surfaces despite its presence.[14] The reasons for this persistence are unknown, although immune tolerance and antigenic variation have been proposed.

The immunological basis of the age-dependent changes in salivary IgA concentrations could be partly explained according to the responses of T-helper (Th) and regulatory T (Treg) cells. Th1 cells are characterized by the secretion of cytokines such as interferon-gamma, whereas Th2 cells produce cytokines such as interleukin (IL)-4, IL-5, and IL-13.[16] Th2 cell secretions, especially IL-5, are responsible for IgA production. Moreover, Treg cells are defined by their ability to produce transforming growth factor-β (TGF-β) which also induces IgA production and inhibits Th2 cell development.[1718] Regarding the results of this study, it seems that up to age 40 years, the Th2 cell responses are responsible for salivary IgA production. Hyperactivation of Treg cells that may occur after age 40 years probably results in higher salivary IgA concentrations through the production of TGF-β. Consistent with our observations, an enhancement in Th2 cell responses and also an elevation in the percentages of Treg cells have been described during aging.[19]

CONCLUSION

The results of the present study demonstrated the profound age-related alterations in salivary IgA levels in healthy individuals. These results encourage further studies to elucidate the precise cellular and molecular mechanisms responsible for these changes to improve oral immunity

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest