Activation of neutrophils is daily inhibited by saliva

The circadian release of superoxide anion (O-2(-)) by inflammatory neutrophils was investigated with mice kept under a constant light regime. Neutrophils were elicited to the peritoneal cavity by injection of 12% sodium caseinate-PBS solution, collected and stimulated to release O-2(-) to the culture milieu upon the addition of phorbol 12-myristate 13-acetate (PMA). The night phase neutrophils were able to release three fold more O-2(-) than day phase cells. Furthermore, the addition of human saliva in neutrophils cultures dramatically inhibits O-2(-) generation. Diurnal human saliva inhibits more effectively neutrophils activation than the nocturnal saliva. The PMA stimulation induces the synthesis of 13 kDa and 14 kDa molecular mass proteins detected in autoradiograms, and saliva additions decrease their synthesis. These two proteins are well known to be essential to the NAD(P)H oxidase assembly complex and, therefore, making neutrophils able to exert their main function as phagocytic cells.