Sepsis is commonly caused by
community-acquired
pneumonia (
CAP) and may develop into
severe sepsis, characterized by
multiple organ failure. The
risk of
severe sepsis among
CAP patients and subsequent
mortality increases sharply after the age of 65. The molecular mechanisms associated with this age-related
risk are not fully understood. To better understand factors involved with increased
incidence and
mortality of
severe sepsis in the
elderly, we used a
nested case-control study of
patients enrolled in a multicenter observational cohort of 2320 participants with
CAP. We identified a total of 39
CAP patients 50-65 and 70-85 years old
who did or did not develop
severe sepsis.
Plasma samples were obtained on presentation to the
emergency department and prior to
therapeutic interventions. A semiquantitative
plasma proteomics workflow was applied which incorporated tandem immunoaffinity depletion, iTRAQ labeling, strong cation exchange fractionation, and nanoflow
liquid chromatography coupled to high-resolution
mass spectrometry. In total, 772
proteins were identified, of which 58
proteins exhibit statistically significant differences in expression levels among
patients with
severe sepsis as a function of age. Differentially expressed
proteins are involved in pathways such as acute phase response, coagulation signaling,
atherosclerosis signaling,
lipid metabolism, and
production of
nitric oxide and
reactive oxygen species. This study provides insight into factors that may explain age-related differences in
incidence of
severe sepsis in the
elderly.