Parotid salivary immunoglobulins, recurrent respiratory tract infections and gingival health in institutionalized and non-institutionalized subjects with Down's syndrome
Dr Stella Chaushu, Clinical Lecturer, Department of Orthodontics, Hebrew University – Hadassah School of Dental Medicine, founded by the Alpha Omega Fraternity, PO Box 12272, Jerusalem 91120, Israel (e-mail: firstname.lastname@example.org).
Background The purpose of the present study was to evaluate the possible correlation between recurrent respiratory infections (RRIs), gingival health and the secretion rates of salivary immunoglobulins (Igs) in institutionalized (I) and non-institutionalized (NI) individuals with Down's syndrome (DS).
Methods Stimulated parotid saliva was collected from nine I and 14 NI subjects with DS. Salivary flow rate, secretion rates of total salivary IgM, IgG and IgA, and the incidence of RRIs were determined. Gingival health was recorded by using the plaque index, the gingival index and the percentage of bleeding surfaces (BS).
Results The mean salivary flow rate and parotid Ig secretion rates in the I group were 25% of those of the NI group. The prevalence of RRIs in the I group was more than twice that in the NI group. Oral hygiene and gingival health were significantly better in the NI group.
Conclusions The lower parotid Ig secretion rates in I individuals with DS might be a possible factor involved in their susceptibility to recurrent infections compared to NI subjects with DS.
Subjects with Down's syndrome (DS) are highly susceptible to chronic recurrent infections (Desai 1997). A definitive causal factor has not been found despite the considerable research that has focused on abnormalities in the immune system of these individuals (Nespoli et al. 1993).
Recurrent respiratory infections (RRIs) have an increased prevalence in people with DS (Siegel 1948). They are among the leading causes of death among these individuals (Oster et al. 1975; Scholl et al. 1982; Bell et al. 1989; Thase 1982; Balarajan et al. 1982), but the reason for the increased prevalence of RRIs in subjects with DS is not clear.
Chronic periodontal disease is also prevalent in subjects with DS under the age of 30 years. Its aetiology is unknown and cannot be explained merely by differences in oral hygiene. Some studies have suggested that institutionalized (I) children with DS have a higher frequency and severity of periodontal disease than those residing at home (non-institutionalized, NI), while others have not detected significant differences (Reuland-Bosma & van Dijk 1986).
The immune protection of both the respiratory system and oral cavity is provided by the common mucosal immune system (CMIS), which represents the first barrier against micro-organisms. The type of immune response in the CMIS is mostly secondary and the dominant antibody isotype is SIgA (Gleeson et al. 1995). The present authors have previously shown abnormalities in the secretion rates of salivary immunoglobulins (Igs) in subjects with DS and have suggested a role for CMIS abnormalities in the high prevalence of recurrent infections (Chaushu et al. 2002).
Therefore, the purpose of the present study was to assess a possible association between RRIs, gingival health and the levels of salivary Igs in I versus NI individuals with DS, in order to provide answers to the pathogenesis of their increased susceptibility to RRIs and gingival inflammation.
Subjects and methods
Twenty-three patients with Down's syndrome (13 males and 10 females) aged 11–22 years (mean age = 18.43.7 years) were included in the present study. Each patient had a typical trisomy of chromosome. 21. Nine patients lived at home, either with parents or with an adoptive family, while the remaining 14 attended the Elwyn Center for the Disabled, Jerusalem, Israel, either as full-time residents (three patients) or as day attendees living off campus in small groups in hostel-like protected apartments (11 patients). The subjects’ medical histories included: recurrent upper respiratory infections (nine patients), hypothyroidism (nine patients), cardiovascular anomalies (five patients), Hirshrung disease (one patient) and Eisenmenger syndrome (one patient). A detailed list of medications used is shown in Table 1. All patients who suffered from hypothyroidism were receiving replacement therapy in the form of Eltroxin (GlaxoSmithKline, Pittsburgh, PA, USA; 50–200 mg day-1), and their thyroid hormone levels were well controlled.
Table 1. Medication in the subjects with Down's syndrome
|Thyroid replacement therapy|| 8|
|Thyroid replacement therapy |
and prophylactic antibiotics
|Prophylactic antibiotics|| 1|
This study was approved by the institutional ethical committee.
Saliva samples were drawn using a parotid salivary gland cup. Salivary secretion was stimulated using 100 L of 2% citric acid applied on the tongue every 15 s over a period of 4–40 min. The total amount of time for the saliva collection was variable since it was dependent on the rate of saliva flow and subject cooperation. It has been shown that flow rates obtained during the initial 2-min interval are closely similar to flow rates of subsequently produced saliva (Baum et al. 1985), and therefore, saliva flow rate was measured from the initiation of the gustatory stimulation in the present study. Saliva samples were collected between 0900 and 1200 h. The patients refrained from eating and drinking for at least 1 h before the collection. The salivary flow rate was expressed in millilitres per minute per gland.
Quantification of salivary immunoglobulins
Total salivary IgM, IgG and IgA were determined by enzyme-linked immunosorbent assay (elisa) using 96-well polystyrene plates (Nunc, Roskilde, Denmark) coated with rabbit antihuman Ig antibodies (BioMakor, Kiryat Weizmann, Rehovot, Israel). At least four salivary dilutions were placed in triplicate wells and incubated for 2 h at 37°C. The plates were washed six times before alkaline phosphatase conjugated rabbit antihuman α, γ or µ heavy chains (Sigma, Sigma-Aldrich, Rehovot, Israel) were added. After further incubation for 1 h at 37°C, the plates were washed again and p-nitrophenylphosphate was added to the wells. Colour development was stopped after 30 min at 37°C by adding sodium hydroxide, and the optical density at 405 nm was determined in an automated elisa reader (Dynatech, Chantilly, VA, USA). Human myeloma proteins, pooled at Hadassah Hospital, Jerusalem, Israel, were used as standards. The standards were calibrated in a commercial agar immunodiffusion assay against reference proteins provided by the manufacturer (Behring Werke, Marburg, Germany). Parallelism between the standard curves based on serum myeloma proteins and the unknown salivary samples tested at different dilutions was a prerequisite for the determination of salivary Ig concentrations.
Classification of clinical manifestations
Data were collected from patient records by a structured questionnaire. The obtained information was confirmed verbally by a personal interview with the treating medical personnel or closest relative. Respiratory infections were defined as recurrent when three or more episodes of bronchitis, tonsillitis, sinusitis, otitis media, common cold or pharyngitis had occurred during the past 12 months. Tonsillectomy and adenoidectomy were also considered to be signs of RRIs.
Clinical recordings were performed on representative permanent teeth (numbers 16, 21, 24, 36, 41 and 44) according to Ramfjord (1959). Whenever one of these teeth was absent, the adjacent tooth was substituted.
Plaque index (PI)
The mesial, distal, lingual and buccal surfaces were scored by one observer on a scale of 0–3 according to Silness & Loe (1964). The mean surface score per tooth was determined by dividing the total score of all surfaces by four. The mean scores of every Ramfjord tooth were then combined to determine the individual's mean score.
Gingival index (GI)
To determine the GI, the same surfaces as for the PI were scored on a scale of 0–3 according to Loe & Silness (1963). The mean score for the individual was calculated as described for the PI.
Bleeding sites (BSs)
Bleeding tendency was calculated as the number of bleeding papillae, expressed as a percentage of all mesial and distal papillae of the Ramfjord teeth, following the gentle interproximal insertion of a wooden toothpick (Shapira & Stabholtz 1996).
The information gathered was statistically analysed using Kruskal–Wallis and Wilcoxon rank sum tests. These non-parametric rank tests were used because the sample size was relatively small and not of normal distribution. All P-values given are based on two-tailed tests and P < 0.05 was the criterion of significance. Differences were evaluated, analysed and compared between the I and NI subjects with DS.
The results of the present study are summarized in Table 2.
Table 2. Comparison of flow rate, Ig concentrations and secretion rates, the incidence of recurrent respiratory infections, and gingival health between institutionalized and non-institutionalized individuals with Down's syndrome
|Age (years)||20.8 ± 1.9||14.7 ± 2.6||< 0.001|
|Flow rate (mL min−1)||0.05 ± 0.03|| 0.2 ± 0.1||< 0.01|
| secretion rate (µg min−1 gland−1)|| 5.2 ± 3.5||23.9 ± 17.9||< 0.01|
| concentration (µg mL−1)|| 112 ± 34|| 121 ± 30||NS|
| secretion rate (µg min−1 gland−1)||0.01 ± 0.001||0.04 ± 0.04||< 0.001|
| concentration (µg mL−1)|| 0.2 ± 0.05|| 0.2 ± 0.05||NS|
| secretion rate (µg min−1 gland−1)|| 1.3 ± 1.2|| 4.2 ± 3.2||< 0.01|
| concentration (µg mL−1)|| 33 ± 18|| 30 ± 21||NS|
|Recurrent respiratory infections|| 7 (50%)|| 2 (22.2%)||NS|
|Plaque index|| 1.5 ± 0.4|| 1.2 ± 0.2|| 0.05|
|Gingival index|| 1.6 ± 0.2|| 1.3 ± 0.2||< 0.01|
|Percentage of bleeding surfaces||60.1 ± 2|| 40 ± 2||< 0.05|
The mean salivary flow rate in the I group of individuals with DS was significantly lower than in the NI group, i.e. 0.05 ± 0.03 versus 0.2 ± 0.1 mL min-1. These values represented a 75% reduction of salivary flow rate in the I group.
Salivary Ig concentrations
Salivary concentrations of IgA, IgG and IgM were similar in both the I and NI groups.
Salivary Ig secretion rates
Significant differences in salivary Ig secretion rates were seen between the I and NI groups. The decrease in the secretion rates of the I individuals was nearly 75%, resembling the decrease in salivary flow rate. Because of the similarity in concentrations between the two groups, the secretion rates reflected the decrease in salivary flow rate.
Recurrent respiratory infections
The prevalence of RRIs was more than double in the I group (50% versus 22.2%), although the small numbers involved precluded statistical analysis.
Lower scores for oral hygiene (PI) and gingival health indices (GI and BSs) showed a significantly higher standard for the NI group of individuals with DS.
It has been suggested that a stressful lifestyle may increase susceptibility to chronic recurrent infections. Comparative studies on the life quality of adults with DS are rare, but a comparison between I and NI subjects with DS showed that NI individuals are more interested in homework and at workplaces, are better motivated, and show a better mood (Schroeder-Kurtz et al. 1990). In another study, quality of life was evaluated through the assessment of an individual's satisfaction with different elements of life. The residents of sheltered apartments expressed the greatest satisfaction, while people living in the residential institution expressed the least (Schwartz & Ben-Menachem 1999). A considerable improvement in the quality of life of people with intellectual disability who have moved from hospital to community-based homes has also been demonstrated (Dagnan et al. 1995).
A significant decrease in the saliva flow rate has been reported in I subjects with DS (Cutress 1972). Other factors reducing salivary flow include psychological factors, such as stress (Bergdahl & Bergdahl 2000), poorer social class (Evans et al. 2000) and situational stress (Somer et al. 1993). The findings of the present study suggest that psychosocial stress may be the major contributor in the 75% decrease in salivary flow observed in I people with DS.
Changes in salivary flow rate may influence the concentrations of the various salivary constituents (Mandel 1980). Therefore, to evaluate salivary composition in abnormal states, one must be aware of the specific relationship of the concentration to the flow rate. Such a relationship is not necessarily constant and may be time- and flow-rate dependent. For example, sodium and chloride are directly related to flow rate, potassium is independent of flow rate in stimulated saliva, while calcium is flow dependent only at the highest flow rates (Mandel 1980). It is for these reasons that researchers working on salivary Igs have considered secretion rate (the product of concentration and flow rate, expressed as µg min-1 gland-1) as the more accurate indicator of mucosal function, since it accounts for individual variations caused by the rate of salivary flow (Brandtzaeg et al. 1970; Brandtzaeg 1971; Chandler et al. 1974; Ørstavik & Brandtzaeg 1975; Challacombe et al. 1995).
The present study indicates an almost 75% decrease in the salivary Ig secretion rate in I individuals with DS, which one may be permitted to speculate is stress related. Because salivary flow and secretion rates were similar, the present results cannot indicate whether psychosocial stress influenced Ig secretion rates in saliva independently of its effects on salivary flow. Nevertheless, it is open to speculation that frequent suppression of mucosal immune response total output by psychosocial stress may increase susceptibility to chronic recurrent infections in organs and tissues protected by the secretory system in subjects with DS.
The prevalence of RRIs in I individuals with DS was more than double than that of subjects living in a home environment. This finding is consistent with previous reports suggesting an association between RRIs and psychosocial stress (Graham et al. 1986; Cohen et al. 1991; Cohen 1995). The same stress factor has been shown to lower SIgA:albumin ratios in children suffering from RRIs (Drummond & Hewson-Bower 1997). The present study proposes psychosocial stress as a possible factor involved in increased susceptibility to RRIs of individuals with DS.
A review of the literature indicates that psychosocial stress is one of the predisposing factors to acute necrotizing ulcerative gingivitis (da Silva et al. 1995). However, available evidence cannot substantiate the hypothesis that psychosocial stress is involved in chronic periodontal disease. Nevertheless, it is clear that some psychosocial measures of stress are significant risk indicators for severe periodontal disease (Genco et al. 1998; Genco et al. 1999). An association between psychosocial factors, adult periodontitis (Moss et al. 1996) and adult-onset rapidly progressive periodontitis (da Silva et al. 1996) has also been suggested.
Individuals with DS demonstrate a high prevalence of periodontal diseases (Desai 1997). Both oral hygiene (PI) and gingival health (GI and BSs) were of a significantly higher standard in NI individuals with DS. The results of the present study indicate psychosocial stress as a possible additional factor involved in the pervasive presence of periodontal disease in subjects with DS. The proposed mechanisms which may mediate such a relationship between psychosocial stress and periodontal diseases remain to be elucidated.
These findings in individuals with DS have led the present authors to propose the following hypotheses:
- 1Psychosocial stress may act either as an initiator or an accelerator of an already existing secretory immunodeficiency.
- 2The functional interaction between psychosocial stress, mediated via the central nervous system, and the immune system may be exerted along two different pathways:
a the nervous ‘wiring’ system that innervates lymphoid tissues and the ‘soluble connection’ via the neuro-endocrine system (Ballieux 1991); and
b a defective humoral mucosal immune response could be the causal agent for recurrent infections in subjects with DS, such as periodontal disease and RRIs.
It would seem logical to encourage the development of therapeutic modalities directed towards two principle goals:
- 1the improvement of the immune status, i.e. specific immunization of the CMIS and local administration of an IgA-enriched preparation (Giraudi et al. 1997); and
- 2the elimination of psychosocial stress, directing more individuals with DS to a home residency programme.
Measurement of Ig levels in saliva in the treated groups provides a simple, effective and non-invasive modality to evaluate the efficacy of immunization or psychosocial programmes.
These measures may result in a reduction in the number of infectious episodes in susceptible individuals with DS. It is reasonable to expert that such efforts will eventually lead to the establishment of appropriate therapeutic protocols, which will ultimately lower the morbidity of RRIs and periodontal disease in individuals with DS.
This work was supported by the joint research fund of the Hebrew University – Hadassah School of Dental Medicine and by a grant from the Alpha Omega Fraternity.