Assessment of serum free light chain levels in healthy adults immediately after marathon running

BACKGROUND: Immunoglobulin κ and λ free light chains (FLC) are important serum biomarkers for diagnosing and monitoring plasma cell dyscrasias (via the κ:λ FLC ratio), and assessing immune competence and activation status (via ∑FLC). FLCs are produced, in excess of heavy chains, from healthy plasma cells during immunoglobulin production, but unlike intact immunoglobulins that are cleared by cellular catabolism over a number of weeks, FLC are rapidly cleared from the bloodstream by the renal glomerulus with a half-life of 3 (κ FLC)-6 (λ FLC) hours. Marathon running has been shown to acutely and transiently decrease renal function, however, the impact of prolonged aerobic exercise on FLC levels remains unknown.

METHODS: We measured serum FLC levels in 60 runners before, and immediately after, the 2010 Eindhoven Marathon.

RESULTS: A significant increase (p<0.01) in κ FLC levels was observed after the marathon, and κ FLC correlated positively with serum creatinine levels. No changes were observed for λ FLC, and thus, there were subtle elevations in the ∑FLC and FLC ratio in some participants. Indeed, we found that 13% of participants had an abnormally increased FLC ratio upon completion of the marathon; a phenomenon previously observed in renal diseases.

CONCLUSIONS: Abnormal FLC ratios observed after exercise reflected an increase in serum κ FLC levels, which may be due to acute and transient reductions in renal function during exercise, though we also observed an increase in serum IgG and IgA and thus cannot exclude exercise-induced immune stimulation or immunoglobulin redistribution.