Protein S declines during winter respiratory infections

Abstract

There is an increase in cardiovascular and cerebro-vascular morbidity and mortality in the older adult population during the winter that could be related to prothrombotic changes caused by seasonal effects or acute respiratory tract infections. Therefore, a prospective cohort study was conducted to assess the effect of acute winter respiratory infection on hemostatic parameters including complement 4b-binding protein (C4-BP), functional protein S, total protein S, free protein S, and the inflammatory marker, interleukin-6 (IL-6), in younger and older adults. The changes in the levels of hemostatic and inflammatory markers during winter respiratory infections in the younger and older adults were compared with matched, non-infected controls. In younger and older adults (combined), total protein S increased from 83% [95% confidence interval (CI); 77-88] to 98% (95% CI; 91-106, P< 0.001) while free protein S decreased from 100% (95% CI; 95-105) to 70% (95% CI; 66-75, P< 0.001). There were no significant changes in C4-BP (P= 0.622), functional protein S (P >= 0.061) or IL-6 (P= 0.651) from baseline. In a multivariate analysis, only total protein S and free protein S showed significant association with seasonal change after adjusting for the effect of infection. The estimated effect of season on total protein S was 15 ± 4%, P< 0.001 and on free protein S was -27 ± 3%, P< 0.001. After adjusting for seasonal effect, only functional protein S showed a significant association with infection, with the estimated effect of -17 ± 5%, P< 0.001. The results in the younger and older adults were similar to those in the combined groups. Seasonal and infection-related changes in hemostatic parameters including an increase in fibrinogen and a decrease in free protein S, observed in this study, may contribute to thrombotic risk and excess vascular disease morbidity and mortality in older populations in the winter season. © 2003 International Society on Thrombosis and Haemostasis.