Muramic acid in peripheral blood leukocytes of healthy human subjects

Peptidoglycan, a specific marker for all bacterial cell walls, was studied in peripheral blood of healthy human subjects by mass spectrometric analysis of muramic acid. Peripheral blood mononuclear and polymorphonuclear cells from 98 healthy adults were hydrolyzed and analyzed by gas chromatography-mass spectrometry as alditol acetate derivatives using selective ion monitoring. Muramic acid was observed in cell samples from 21 of 98 subjects. Blood cultures were done simultaneously and remained negative. As a control, mononuclear and polymorphonuclear cells separated from umbilical vein blood of 41 healthy newborns were studied; all were muramic acid-negative. Since newborns lack gut flora, intestinal absorption of bacteria or of their degradation products appears to be the most likely explanation for the finding.