We investigated the immunity and the main factors that affect the immune system of 19 truck drivers as the experimental group and 27 office workers as the control group at a transit corporation in Tokyo; all subjects in both groups were examined through an assay of NK activity and NK subsets before and after work. At the same time, they were asked to complete a questionnaire on their working hours per day (WHPD) and driving hours per day (DHPD), in addition to the Health Practice Index (HPI), Self-Rating Depression Scale (SDS), Stress Tolerance Check List (STCL), and Symptom Checklist (SCL). The results obtained were as follows:
1. Before work, no difference was seen in NK activity between the experimental group and the control group, with both groups showing E:T ratios 5:1 to 20:1. After work, the NK activity (E:T=20:1) of the experimental group was significantly lower than that of the control group.
2. In the experimental group, the NK activity and NK subsets (CD3-CD16+CD56+, CD3-CD56+, CD3-CD16+) of the peripheral blood lymphocytes after work were significantly lower than before work (p<0.05, p<0.01, p<0.01). After more than five driving hours, the value of the CD3-CD16+CD56+ subset was significantly lower than that after fewer driving hours.
3. Correlation coefficients were calculated based on the average value of NK activity (E:T=20:1), CD3-CD16+CD56+ subset, and WHPD, DHPD, and HPI in the driving group. NK activity (E:T=20:1) and DHPD were found to be negatively correlated (r=-0.28), as were the CD3-CD16+CD56+ subset and WHPD (r=-0.43) and the CD3-CD16+CD56+ subset and DHPD (r=-0.63). On the other hand, NK activity (E:T=20:1), the CD3-CD16+CD56+ subset and HPI were found to be positively correlated (r=0.41 and 0.33).
