The randomised, double-blind, placebo-controlled, parallel-group comparative trial, conducted by authors from Japan, concluded: “LG2055 suppresses the subjective symptoms of the common cold by activating plasmacytoid dendritic cells (pDCs) and improving the host’s immune system in healthy adults, especially in immune-weakened individuals.”
The study included 200 participants who were randomly divided into two groups and consumed three capsules with or without LG2055 daily for 12 weeks.
Based on scores from a daily physical health questionnaire survey of common cold symptoms, the LG2055 group showed a significantly higher ratio of “without symptoms” responses for runny nose, plugged nose, sneezing, sore throat, hoarseness, and chill than the placebo group.
pDCs, a rare immune cell type, have received recent research attention in the realm of immune health, as they are important for the response to viral infections.
Activated pDCs produce large amounts of type I interferons (polypeptides that are secreted by infected cells) and activate many types of immune cells, such as natural killer (NK) cells, B cells, and T cells, which enhance the immune system and protect the host from infection.
Although pDC activation is usually induced by the recognition of viral DNA or RNA during viral infection, the authors suggest that agents that activate pDCs can be used to enhance the host’s defence system without viral infection.
Several food ingredients such as the protein lactoferrin and its digestive peptide, have been reported to activate pDCs.
Moreover, some non-pathogenic bacteria, such as lactic acid bacteria (LAB), have been reported to activate pDCs in previous clinical trials.
The authors of the new study state: “The availability and functionality of LAB are well-known. Therefore, we hypothesised that the continuous intake of LAB which activates pDCs could enhance the host’s immune system.”
Lactobacillus paragasseri SBT2055 (LG2055) is a LAB strain (previously classified as Lactobacillus gasseri ) used for manufacturing dairy products, that has been shown to have beneficial effects, including a reduction of oxidative stress and an improvement of the intestinal environment.
Moreover, the immunostimulatory effects of LG2055, such as suppression of viral infection, induction of immunoglobulin A (IgA) production, and an increase in hemagglutination inhibition levels against the influenza virus after vaccination, have been previously investigated. Therefore, the authors theorised that LG2055 could maintain and/or improve the host’s immune system.
A previous study by the same authors examined whether LG2055 could diminish the subjective symptoms of the common cold in healthy adults, finding that the supplemented group showed significantly higher salivary levels of secretory IgA (sIgA), which could reflect an activated immune response to chronic infection, and significantly lower levels of oxidative stress markers.
The authors explain: “These results suggest that LG2055 may improve the host’s immune system and suppress the symptoms of the common cold and imply that the ability of LG2055 to activate innate and/or acquired immunity and its antioxidative effects contributed to these results.”
They therefore expected that the activation of pDCs would contribute to the immunostimulatory effects of LG2055, and aimed to perform in vitro experiments and a randomised controlled trial (RCT) aiming to evaluate whether LG2055 activates pDCs and suppress common cold symptoms in healthy adults.
This study was conducted from October 2022 to May 2023, with participants comprising healthy Japanese males and females aged 20–64 years who frequently caught colds.
Participants answered a health questionnaire every day and received a medical doctor’s consultation four times during the study (at screening test and at 0, 6, and 12 weeks).
Saliva and blood samples were collected during the screening test and at 0, 6, and 12 weeks after the start of intake, and faecal samples were collected at 0 and 12 weeks.
Results from the RCT suggest that daily intake of LG2055 decreased the cumulative days of common cold symptoms in healthy adults.
The LG2055 group additionally showed significantly lower ratios of cumulative days of several local and systemic symptoms than the placebo group.
There was no significant difference in pDC activity (expression levels of CD86 and HLA-DR) between the LG2055 and placebo groups.
However, the stratified analysis intended for immune-weakened participants found that LG2055 intake enhanced the expression of CD86 and HLA-DR (a marker of the pDC activity) on pDCs in participants who showed low salivary sIgA secretion rates (a potential sign of weakened-immunity)
The authors conclude that these findings indicate that LG2055 contributed to the maintenance of the physical condition by activating pDCs and improving the host’s immune system.
They however note: “Differences in the host’s gut microbiota have been supposed to cause differences in stimuli at a steady state and may affect the expression of the effects of LG2055.
“With further exploration and research, the relationship between the specific differences in the host’s gut microbiota and pDC activation is expected to be better understood.”
Lactobacillus paragasseri SBT2055 Activates Plasmacytoid Dendritic Cells and Improves Subjective Symptoms of Common Cold in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Parallel-Group Comparative Trial