<p>Ancient traditional Chinese medicine (TCM) doctrine says “The superior doctor prevents illnesses,” pointing out preventative medicine as the ultimate goal for medical care. TCM recognizes that genetic predisposition and environmental and lifestyle influences contribute to diseases. It divides people into eight constitutions in addition to one normal/healthy kind. People with one of the eight subhealth constitutions are prone to develop different kinds of corresponding illnesses. The goal for this type of categorization is to help people take preemptive measures to prevent or delay disease onset. As the peripheral immune system through surveying the body, it can capture information from essentially all organs and reflect anomalies occurring in each organ. Thus, the detailed profiling of the peripheral immune-system function can generally reflect a person’s overall heath state. In this study, we performed the single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from individuals with Tanshi (phlegm dampness) constitution. They were prone to develop metabolic disorders including diabetes. scRNA-seq revealed greatly reduced mucosal-associated invariable T cell content and heightened TNFα-NFκB, JAK-STAT, and interferon signaling. These findings indicated heightened chronic inflammation, as well as increased hypoxia/apoptosis responses, likely resulting from frequent sleep apnea that Tanshi individuals experienced. Altogether, this pilot study demonstrated effectiveness in using scRNA-seq to reveal molecular-immunological bases for constitution categorization, thereby substantiating that preventative medicine originated from TCM.</p>