The meta-analysis included eight clinical trials extracted from databases including PubMed, Cochrane Library, J-Dream III, UMIN-CTR and the International Clinical Trials Registry Platform through June 21, 2024.
Studies examined the effects of LC-plasma supplementation on pDC activation and common cold-like symptoms in a total of 746 healthy adults, with interventions periods ranging from 13 to 84 days. Two studies were conducted using live LC-plasma, while the remaining six studies used heat-killed LC-plasma. In all studies, the daily intake was set at 10bn cells of LC-plasma.
All eight clinical trials and the current meta-analysis, were funded by Japanese company Kirin Holdings Company, Limited, which markets LC-Plasma, which is sold as IMMUSE in the U.S. and European markets.
Findings indicated that cold symptoms, such cough and feverishness, were significantly reduced in individuals who took LC-Plasma as compared to those taking a placebo. No significant improvements were seen in other symptoms, such as sore throat and runny nose.
pDC activation
Another key finding was that a group of immune cells, specifically pDC, was upregulated with LC-plasma intake.
This was gleaned from the significantly higher amount of pDC activation markers CD86 among individuals who have taken LC-plasma, based on six out of the eight clinical studies that evaluated CD86 expression levels.
CD86, in this case, plays a innate and adaptive immune systems.
Based on recent studies, the upregulation of CD86 in pDCs indicates cellular activation and is crucial for providing co-stimulatory signals to T cells. This, in turn, enhances antigen presentation and bridges innate and adaptive immunity.
Another pDC activation marker, HLA-DR, also saw a significant increase in expression levels based on five out of the eight clinical studies included in this meta-analysis.
“LC-plasma was identified as a unique strain of lactic acid bacteria that activates pDCs, and multiple studies have tested its effects on pDC activation and the prevention of cold-like symptoms,” the researchers wrote. “These previous studies enabled us to comprehensively verify the effects of LC-plasma in the present study.”
They added that the study is the first to present, through integrated analyses using identical analytical conditions, that daily intake of LC-plasma may help sustain pDC activation and could be useful in reducing cough and feverishness, typical cold-like symptoms.
Further studies
A limitation of this meta-analysis was the lack of evidence on the effects of LC-plasma in non-Asian populations, as well as the elderly, children and immunocompromised individuals, the researchers pointed out.
As such, they called for future intervention trials examining the effects of LC-plasma supplementation on carefully defined participants, as well as optimal timing of long-term intervention.
Another limitation was the inability to quantitatively and objectively assess actual fever, instead of feelings of “feverishness” which is a subjectively evaluated indicator.
In this case, the researchers have proposed the use of tests that used body temperature as an evaluation index to verify the effects of LC-Plasma intake on fever.
Source: Frontiers in Immunology, 16:1696989. doi: 10.3389/fimmu.2025.1696989. "Lactococcus lactisstrain Plasma activates plasmacytoid dendritic cells and mitigates common cold-like symptoms in healthy adults: a meta-analysis of individual participant data". Authors: Kato Y et al.
