A soluble form of Toll-like receptor 2 (sTLR2), a receptor of the immune system critically involved in pro-inflammatory responses, is present in human plasma and other bodily fluids showing anti-inflammatory potential, acting as a decoy receptor to limit inflammation.

Notably, elevated levels of sTLR2 are present early on in patients with sepsis, and other infective and non-infective inflammatory conditions, with a rapid kinetics of release. Elevated sTLR2 levels can be detected in plasma after just 30 minutes following cell stimulation by bacterial products, reaching peak concentration after just 4 hours, and has a very short half-life.

This represents a potential advantage of sTLR2 as a biomarker of early sepsis over C-reactive protein (CRP) and procalcitonin (PCT). CRP exhibits a slower kinetics of release, as it only begins to rise after 12-24 hours of the insult, peaking within 2-3 days, and PCT becomes elevated after 3-4 hours and peaks at about 6-24 hours.

A study of the use of sTLR2 versus CRP in critically ill patients compared with non infective systemic inflammatory response syndrome (SIRS), showed that sTLR2 has better specificity and sensitivity for sepsis than CRP, the most commonly used marker in the ICU (AUC sTLR2 0.959; CRP 0.764).

Further, sTLR2 levels below 1 ng/mL had good ability to rule out sepsis, whether it was secondary to bacterial or fungal infection, within the first 12 h of ICU stay, when clinical parameters and traditional markers of infection are often equivocal.