Lipopolysaccharide (LPS) is a molecule formed by lipids and polysaccharides and is the major cell wall component of gram-negative bacteria. High LPS levels are known to block CD26 expression by activating Toll-like receptor 4. The aim of this study was to correlate the serum levels of LPS and CD26 in Crohn's disease (CD) patients with serum levels of C-reactive protein (CRP), interleukins, CD activity index, and tumor necrosis factor-α (TNF-α).

Serum samples were collected from 27 individuals (10 with active CD, 10 with inactive CD, and 7 controls) and the levels of LPS, CD26, TNF-α, interleukin-1β (IL-1β), IL-6, IL-17, and CRP were determined by enzyme-linked immunosorbent assay. The levels of LPS and CD26 were then tested for correlation with TNF-α, IL-1β, IL-6, IL-17, and CRP.

Serum levels of LPS were significantly elevated in the active CD group ( P =0.003). Levels of IL-1β ( P =0.002), IL-6 ( P =0.003), and IL-17 ( P <0.001) were lower in the CD groups. Serum TNF-α levels were increased in the active CD group. The CRP levels were elevated in the CD groups when compared to controls ( P <0.001). The CD26 levels were lower in the CD groups than in the control group ( P <0.001). Among the variables analyzed, there was a correlation between LPS and CRP (r=−0.53, P =0.016) in the CD groups.

Individuals with CD exhibited higher serum levels of LPS varying from a 2- to 6-fold increase depending on disease activity, when compared with healthy controls. CD26 levels were lower in the CD groups. Both LPS and CD26 correlated with disease severity and serve as potential CD biomarkers.