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Evaluation of salivary IgA as a potential stress biomarker for use in military training

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Pacqué, PFJ 2007 , 'Evaluation of salivary IgA as a potential stress biomarker for use in military training', PhD thesis, University of Tasmania.

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Abstract

Exercise and psychological stress can cause a transient decrease in salivary IgA (s-lgA) and regular intense physical activity can result in a chronic decrease in s-IgA. Epidemiological evidence supports the concept of an association between low levels of s-lgA and the incidence of upper respiratory tract infections (URTI) and overtraining syndrome (OTS). However, the relationships are not strong.
The impact of stress on immune function is of interest to the Australian Defence Force. Soldiers are often subjected to high levels of physiological and psychological stress, and thus susceptible to impaired mucosal immune function and an increased risk of URTI, which could reduce their performance. Newly enlisted recruits may also be susceptible to OTS as they do not necessarily have a very high level of physical fitness. The purpose of this study was to assess the usefulness of s-lgA as an indicator of mucosal immune function, the effect of a variety of stressors on mucosa! immune function and its relationship to the incidence of symptoms of illness and OTS. Preliminary work raised some concerns regarding the reliability of s-lgA. The main weaknesses identified were the possible effects of diurnal variation, the large biological variation, the standardisation of the s-IgA assay, and the collection, handling and storage methods of saliva samples. These issues were addressed by several preliminary experiments and recommendations were made (Chapter 2). Athough s-IgA can be expressed in several ways (as a concentration, a secretion rate, a ratio to secreted protein, or as a ratio to osmolality), only s-lgA secretion rate and s-IgA:osmolality ratio are used in the experimental chapters 3 to 5.
An 82 km ultra-endurance running race was the first opportunity to test the methods developed for the collection, storage and transport of saliva under "field conditions" (Chapter 3). The race resulted in a transient decrease in s-lgA and several other immune parameters.
Soldiers who engaged in two hours of load carriage (Chapter 4) experienced changes in heart rate, metabolic rate, core temperature and perceptions of effort and thermal strain. These changes were greater with higher environmental temperatures and humidity. Only the hottest, most humid environment resulted in a significant decline of s-lgA. Therefore, it seems that if exercise at an intensity that by itself does not cause a significant mucosal immunosuppression is performed in a harsh climate, the resulting hyperthermia can magnify the s-lgA response.
A six week army common recruit training course (Chapter 5) resulted in a high incidence of mucosal immunosuppression and self-reported symptoms ofURTI. There was also a significant incidence of OTS symptoms.
Despite these findings, this work does not lend strong support to the notion that s-IgA could be a practical tool to monitor mucosal immune function or physiological strain in the military. Nor does it seem a good predictor of ill health or early states of OTS.

Item Type: Thesis - PhD
Authors/Creators:Pacqué, PFJ
Keywords: Immunoglobulins, Immune system, Military education
Copyright Information:

Copyright 2007 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (PhD)--University of Tasmania, 2007. Includes bibliographical references. Ch. 1. General introduction -- Ch. 2. Methodological considerations associated with the measurement of salivary IgA -- Ch. 3. Immune changes and upper respiratory tract infections after an ultra-endurance run -- Ch. 4. Hyperthermia and the mucosal immune response to load carriage -- Ch. 5. Salivary IgA, military training and overtraining syndrome -- Ch. 6. General discussion and conclusion

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