Tear Fluid SIgA as a Noninvasive Biomarker of Mucosal Immunity and Common Cold Risk.
OBJECTIVE
Research has not convincingly demonstrated the utility of saliva secretory immunoglobulin-A (SIgA) as a biomarker of upper respiratory tract infection (URTI) risk, and disagreement exists about the influence of heavy exercise ("open-window theory") and dehydration on saliva SIgA. Prompted by the search for viable alternatives, we compared the utility of tear and saliva SIgA to predict URTI prospectively (study 1) and assessed the influence of exercise (study 2) and dehydration (study 3) using a repeated-measures crossover design.


METHODS
In study 1, 40 subjects were recruited during the common-cold season. Subjects provided tear and saliva samples weekly and recorded upper respiratory symptoms (URS) daily for 3 wk. Real-time PCR confirmed common-cold pathogens in 9 of 11 subjects reporting URS (82%). Predictive utility of tear and saliva SIgA was explored by comparing healthy samples with those collected during the week before URS. In study 2, 13 subjects performed a 2-h run at 65% V˙O2peak. In study 3, 13 subjects performed exercise heat stress to 3% body mass loss followed by overnight fluid restriction.


RESULTS
Tear SIgA concentration and secretion rate were 48% and 51% lower, respectively, during URTI and 34% and 46% lower the week before URS (P < 0.05), but saliva SIgA remained unchanged. The risk of URS the following week increased ninefold (95% confidence interval, 1.7-48) when the tear SIgA secretion rate was <5.5 μg·min(-1) and sixfold (95% confidence interval, 1.2-29) when the tear SIgA secretion rate decreased >30%. Tear SIgA secretion rate >5.5 μg·min(-1) or no decrease of >30% predicted subjects free of URS in >80% of cases. Tear SIgA concentration decreased after exercise (-57%, P < 0.05) in line with the "open-window theory" but was unaffected by dehydration. Saliva flow rate decreased and saliva SIgA concentration increased after exercise and during dehydration (P < 0.05).


CONCLUSIONS
Tear SIgA has utility as a noninvasive biomarker of mucosal immunity and common-cold risk.
1College of Health and Behavioural Sciences, Bangor University, Bangor, Gwynedd, UNITED KINGDOM; 2Centre for Infection and Immunity, Queen's University Belfast, Northern Ireland, UNITED KINGDOM; and 3Regional Virus Laboratory, Royal Victoria Hospital, Belfast, UNITED KINGDOM.
Helen G
HG
Hanstock
Neil P
NP
Walsh
Jason P
JP
Edwards
Matthew B
MB
Fortes
Sara L
SL
Cosby
Aaron
A
Nugent
Tanya
T
Curran
Peter V
PV
Coyle
Mark D
MD
Ward
Xin Hui Aw
XH
Yong
D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000737:chemistry; D003139:Common Cold / Q000175:diagnosis*; D018592:Cross-Over Studies; D003681:Dehydration / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D018928:Immunity, Mucosal; D007071:Immunoglobulin A, Secretory / Q000737:chemistry*; D008297:Male; D011446:Prospective Studies; D012307:Risk Factors; D012463:Saliva / Q000737:chemistry; D013666:Tears / Q000737:chemistry*; D055815:Young Adult
D015415:Biomarkers; D007071:Immunoglobulin A, Secretory