Salivary immunoglobulin free light chains: Reference ranges and responses to exercise in young and older adults

Background: Free light chains (FLCs) have a range of biological functions and may act as a broad marker of immune suppression and activation and inflammation. Measurement of salivary FLCs may provide practical advantages in a range of clinical populations. The aim of the present study was to develop normal reference ranges of FLCs in saliva and assess the effects of acute exercise on FLC levels in younger and older adults. Methods: Saliva FLC concentrations and secretion rates were measured in young (n = 88, aged 18–36) and older (n = 53, aged 60–80) adults. To assess FLC changes in response to acute exercise, young adults completed a constant work-rate cycling exercise trial at 60% VO2max (n = 18) or a 1 h cycling time trial (TT) (n = 10) and older adults completed an incremental submaximal treadmill walking exercise test to 75% HRmax (n = 53). Serum FLCs were measured at baseline and in response to exercise. Results: Older adults demonstrated significantly higher levels of salivary FLC parameters compared with young adults. Median (5–95th percentile) concentrations were 0.45 (0.004–3.45) mg/L for kappa and 0.30 (0.08–1.54) mg/L for lambda in young adults; 3.91 (0.75–19.65) mg/L for kappa and 1.00 (0.02–4.50) mg/L for lambda in older adults. Overall median concentrations of salivary kappa and lambda FLCs were 10-fold and 20-fold lower than serum, respectively. Reductions in salivary FLC concentrations and secretion rates were observed immediately post- and at 1 h post exercise, but were only significant for the older cohort; FLCs began to recover between post and 1 h post-exercise. No changes in serum FLCs were observed in response to exercise. Conclusions: The ability to assess FLCs in saliva and the reference ranges provided will likely broaden the use of this biomarker in healthy and clinical populations. The elevated salivary FLCs in older adults may relate to a deterioration of oral health and be important in the context of inflammatory processes and diseases associated with ageing. Exercise did not affect serum FLCs, but reduced salivary FLCs, most notably in older adults, which may reflect reduced transport of FLCs from serum into saliva.