However, acute infectious illnesses or chronic inflammation likely did not cause the up-regulation of the type I IFN responsive genes in the priests because no apparent infection signs and symptoms were observed in any of the participants on the day of the experiment, and no significant difference were detected in the plasma CRP levels (P = 0.47), which is a systemic inflammatory marker, between the priests and the non-priest controls (Additional file 1). This evidence concerns the gene CRP and infection.