CX3CL1 and susceptibility to pneumonia measurement: In further support of this hypothesis, our findings show that plasma levels of interleukin-8, procalcitonin, ST2, fractalkine and TNFR-1 (biomarkers of inflammation and pneumonia) are inversely correlated with the levels of anti-inflammatory purines (adenosine + inosine + guanosine) in the urine.