The efficiency of the immune system declines with age, making older individuals less resistant to infections of pathogenic microorganisms. The worldwide increase in the aging population poses challenges for the healthcare community. Older age is associated with a higher burden of chronic diseases [1]. For example, previous studies have correlated aging with lower cognitive ability and dementia [2,3]. Additionally, the presence of comorbid conditions in the geriatric population increases their vulnerability to acute illnesses such as infections [4]. Therefore, protective, preventive, and remedial factors that can counteract or delay disease manifestation must be explored. Increased physical activity among older adults decreases the risk of cognitive decline and infection [5,6]. Moderately active individuals were less susceptible to infectious diseases than those who were inactive [7–9].

In response to these findings, there has been a growing interest in the effects of exercise on mucosal immunity, particularly in terms of concentrations of secretory immunoglobulin A (SIgA), the major antibody in mucosal secretions such as in the salivary glands [10-12] Secretory immunoglobulin A is secreted by B cells sur-rounding the salivary glands [12]. Salivary SIgA levels have been linked to physical activity, which is measured as the weekly amount of time spent in sports [13]. Therefore, physical activity may effectively prevent infections by enhancing salivary SIgA levels. Geriatric residents in long-term healthcare facilities may demonstrate a trend of decreased activity, and increased risk of infection due to communal living. However, older people may be independent in their activities of daily living (ADL), and those residing in an area may be able to perform their activities by themselves. However, there are few studies evaluating the association between SIgA and ADL within this population. Therefore, we aimed to investigate the association between mucosal immunity and mobility, as indicated by SIgA secretion, and the relationship between ADL among bedridden older residents in a long term health care facility and community-dwelling older people.

Participants were selected from among geriatric residents in a long-term health care facility that provided medical and nursing care and from among community-dwelling older people who used a day service in Saga, Japan. The pool of eligible participants comprised 24 residents and 9 community-dwelling older people aged ≥65 years who were at the facility from January to March 2019. Of these, 10 were excluded because of physi cian-diagnosed bronchiectasis, leaving a total of 23 participants (14 bedridden older residents of a long-term health care facility and 9 community-dwelling older people).

Data on Physical Aspects and Cognitive Function

Age, height, weight, and body mass indices were noted for each participant. Cognitive function was evaluated using the Mini-Mental State Examination (MMSE). Scores ≥24 indicate uncompromised cognitive function, whereas scores ≤10 indicate severe cognitive impairment. The reliability and validity of this standard were inspected previously [14].

Saliva Collection and SIgA Concentration Measurement

Saliva was collected between January and March 2019 using Sarivetee TM (Salimetrics, Carlsbad, CA, USA). Data were collected between 9:00 am and 11:00 am, following breakfast and subsequent oral care. The time required for saliva collection was measured, and the SIgA concentration was determined from the samples using a Salimetrics® SIgA Indirect Enzyme Immunoassay Kit.

Calculation of Salivation Speed

Higher salivation speeds result in increased saliva in the oral cavity. As the concentration of salivary SIgA decreases with increasing saliva, SIgA concentrations are low at high salivation speeds. Salivation speed (mL/min) was calculated based on the time required to collect a specified amount of saliva.

SIgA Secretion Speed

As SIgA concentrations are affected by the quantity of saliva secreted, the SIgA secretion speed was computed as the salivation speed multiplied by the SIgA concentration. This value was used as an index of SIgA production. Secretory immunoglobulin A secretion levels were considered high when the SIgA secretion rate was high.

Classification of ADL Groups

Participants were divided into two groups according to their ADL in the long term health care facility that provided medical and nursing care and local older residents who were capable of walking. The bedridden group comprised the remaining 14 which stay in the long-term health care facility; and 9 community dwelling elderly people, who were confined to their beds, except for meals, and required assistance for all ADLs.

Data Analysis

Multiple comparisons were performed using the Wilcoxon rank sum test to compare mean age, height, weight, BMI, MMSE scores, salivation speed, SIgA concentration, and SIgA secretion speed among the two groups (the bedridden group and the community-dwelling older people group). SPSS Statistics for Windows (version 29.0; IBM Corp., Armonk, USA), was used for all statistical analyses, with the significance level set at 0.05.

Ethical Considerations

Written informed consent was obtained from all the participants. The study was approved by the Institutional Review Board of JCHO Saga Central Hospital and the International University of Health and Welfare and was conducted according to the principles set out in the Declaration of Helsinki.

The sample population comprised more women than men. Age and weight were roughly equivalent be-tween the two groups (Table 1). The average MMSE scores of the entire sample and the bedridden residents and community dwelling older people fell within the moderate impairment range. The scores of the bedridden residents were in the severely impaired range and were significantly lower than those of the community- dwelling older (p<.001 for both comparisons).

The bedridden residents also had significantly higher SIgA concentrations in the saliva (p<.01) and higher SIgA secretion speeds (p<.05) as compared to those in the community- dwelling older people. There were no differences in the salivation speed between the two groups.

The medical conditions of the participants were not associated with salivation speed, SIgA concentration, and SIgA secretion speed. However, our data suggested significant negative correlations between MMSE scores and SIgA concentration (r=- 0.413, p<.05) (Figure 1) and between MMSE scores and SIgA secretion speed (r=-.338, p<.05) (Figure 2).

Table 1: Demographics of the study groups.

We compared the mean age, weight, MMSE score, salivation speed, SIgA concentration and SIgA secretion speed in the groups (Wilcoxon rank sum test) .

***p <.001                **p <.01            *p <.05

Figure 1: Relation between MMSE score and SIgA concentration (µg/mL).

Figure 2: Relation between MMSE score and SIgA secretion speed (µg/mL).

This study aimed to explore the association between mucosal immunity and mobility. We investigated the association between SIgA concentration and ADL levels among older residents in a long-term health care facility.

The results of this study revealed significantly higher SIgA levels in bedridden residents than those in community-dwelling older individuals. Additionally, the SIgA secretion rate in bedridden residents was significantly higher than that in community dwelling older people. The results of this study revealed an inverse relationship between the indicators of mobility (ADL) and mucosal immunity (SIgA concentration) in geriatric residents in the long-term health care facility in Japan, as hypothesized. This was demonstrated by the significantly higher salivatory SIgA concentrations and secretion speeds in bedridden patients compared to those in those who could move using walking support or a wheelchair. Notably, these results suggest that mobility is inversely correlated with SIgA levels.

Our findings are consistent with those of previous studies [15-17]. Taito et al [18]. reported that the SIgA secretion rate in hospitalized older patients is higher than that in patients using outpatient services. Furthermore, the SIgA level is higher among older inpatients than that among the non-hospitalized geriatric population [19]. The comparable setting of long-term healthcare facilities and that of constant medical and nursing care pro-vided to bedridden residents may be implicated in their increased SIgA concentration and SIgA secretion speed.

In addition, our analyses revealed negative correlations between MMSE scores and both SIgA concentration and secretion speed in bedridden residents, thereby associating cognitive impairment with high SIgA secretion. Kojima et al. found that a low MMSE score among older individuals was a risk factor for malnutrition and infection [20] Dedicated care provided to bedridden older residents in long-term healthcare facilities may reduce the risk of malnutrition and infection. From a prophylactic perspective, it would be interesting to investigate the benefits of comparable dedicated care for ambulant and wheelchair-bound geriatric residents in long-term health care facilities.

In addition to the insights gained from the results, our data raise several possibilities for direct future re-search. Secretory immunoglobulin A, an antimicrobial found in secretions, is a useful stress evaluation index. Indeed, its levels decrease with chronic stress [21]. We postulate that the reduced SIgA concentrations among our ambulant participants could be the result of increased stress in this population. Communal living can be a source of substantial emotional strain that negatively influences patient health [22]. Therefore, our study could be extended to objectively evaluate stress in this population. Another consideration would be regarding daily changes in SIgA concentration and its effect on associated factors, as the concentration of SIgA can fluctuate within an individual throughout the day [23,24] Finally, similar studies involving larger sample sizes and the quantification of functional abilities can improve generalization and minimize associated biases.

Acknowledgements

This study was supported by the Japan Community Health care Organization (JCHO) in Saga prefecture, Japan, Nishikyushu University. The authors thank Dr. A. Danjyo at the JCHO Saga Central Hospital, for their encouragement, advice, and support of the study; Mr. M. Ishibashi at the JCHO Saga Central Hospital, for his encouragement of the study; and Ms. M. Hattori at the JCHO Health Administration Center, for her skilled technical assistance. We would like to thank Editage (www.editage.jp) for English lan- guage editing.

Conflicts of Interest

None declared.

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