Effects of Lactococcus lactis Strain Plasma (LC-Plasma) Intake on Infection-Related Symptoms Among Healthcare Workers: A Randomized, Double-Blind, Placebo-Controlled Study.

The rising health threat to healthcare workers (HCWs) demands innovative preventive solutions that are affordable, scalable, and easy to deploy, especially in resource-limited settings. This present study investigated the effects of Lactococcus lactis strain Plasma (LC-Plasma) intake on upper respiratory infection (URI)-like symptoms in a healthy healthcare-associated population in Vietnam. A randomized, placebo-controlled, double-blind, parallel-group clinical trial was conducted, integrating clinical symptom analysis with ex vivo immune response analysis of peripheral blood mononuclear cells (PBMCs). The study found that after 4 weeks of continuous oral LC-Plasma intake, participants in the LC-Plasma group had significantly fewer cumulative days of fever and fatigue than those in the Control group. Increased expression of interferon-stimulated genes (ISGs), particularly MxA, was observed in PBMC cultures from the LC-Plasma intake group. In PBMCs from LC-Plasma recipients classified as low IFN-α responders, the addition of CpG ODN 2216, a mild TLR9 agonist, significantly enhanced interferon-α production. Humoral factors derived from LC-Plasma-primed PBMCs demonstrated inhibitory effects on dengue virus replication in Huh-7 cells. These results suggest that LC-Plasma consumption by the healthcare-associated population reduces the severity of viral infection symptoms, notably fever and fatigue. Elevation of systemic antiviral immunity through activation of plasmacytoid dendritic cells (pDCs) to produce IFN-α and upregulation of ISG expression could be the mechanisms of action. Lactococcus lactis LC-Plasma supplementation, hence, presents a promising adjunctive approach to alleviate the burden of URI-like symptoms in low-resourced vulnerable populations.