**5. Conclusions**

Herein, we have demonstrated that boatyard workers continue to be exposed to toxic high levels of Pb, as reflected by their blood Pb levels, which are 8.7-fold higher than the farmer control group. The immunological effects associated with such toxic exposure levels among study workers are reduced phagocytic activity, altered cytokine profiles (an increase in IL-4 concomitant with a decrease in IFN-γ), and deranged subpopulations of Tc and Treg cells, causing suppression of cell-mediated immunity. These findings may explain the increased risk of death from cancer and increased incidence of lung cancer and brain cancer in workers with high exposure, seen in cohort studies of Pb-exposed workers [13,14]. Public measures are required in order to reduce workplace exposure, as is a further study with a larger sample size to substantiate these important observations.

**Author Contributions:** Conceptualization, W.K. and S.Y.; methodology, K.P.; software, W.K.; formal analysis, K.P. and W.K.; investigation, K.P.; resources, S.Y., K.P., and W.K.; writing—original draft preparation, K.P. and W.K.; writing—review and editing, W.K. and S.Y.; supervision, W.K.; project administration, W.K.; funding acquisition, W.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Walailak University Research Funds (grant number 18/2557 and 15/2559) and partially supported by the New Strategic Research (P2P) project, Walailak University, Thailand.

**Acknowledgments:** We would like to thank the Center of Excellence Research for Melioidosis (CERM) and School of Allied Health Sciences, Walailak University, Nakhon Si Thammarat 80160, Thailand, for providing the equipment.

**Conflicts of Interest:** The authors declare no conflict of interest.
