The relationship between the frequency of the common cold and the activities of natural killer cells.

We investigated the relationship between the frequency of the common cold and the conditions of the body's immune system among members of a generally healthy population. Self-reporting questionnaires on the frequency of the common cold and on fatigue and stress conditions were administered to a total of 67 healthy individuals aged 22 to 50. The activities of natural killer (NK) cells, which were determined by Eu(3+)-DTPA release assay, and of NK cell members in the peripheral blood of the subjects were phenotypically (CD3 CD16(+) CD56(+)) analyzed with three-color flow cytometry. The results showed that the frequency of the common cold was significantly correlated with NK activity and NK subset (CD3(-)CD16(+) CD56(+)) frequency (r=-0.34 and-0.47 respectively, P<0.01). After adjusting for age, the mean NK subset (CD3(-)CD16(+)CD56) significandy differed (F=3.384, P<0.05) among the four frequency groups for the common cold, and the frequencies of the common cold were significandy different among the four stress/fatigue groups (F=8.016, P<0.001) for the males, as evaluated by ANCOVA. These results indicate that conditions of high stress and fatigue may increase the chance of catching the common cold due to a decrease in activities of NK cells.