title: Oral intake of heat-killed Lactobacillus plantarum L-137 decreases the incidence of upper respiratory tract infection in healthy subjects with high levels of psychological stress.
abstract: The immunomodulatory effects of live or non-viable lactic acid bacteria have been extensively investigated. We reported that oral intake of heat-killed Lactobacillus plantarum L-137 (HK L-137) augmented innate and acquired immunity in mice and human subjects. To examine the effects of HK L-137 intake on upper respiratory tract infection (URTI) symptoms and immune functions in human subjects, a randomised, double-blind, placebo-controlled, parallel study was conducted in subjects with high psychological stress levels. A total of seventy-eight healthy subjects (thirty-three men and forty-five women; mean age 50·6 years) with scores of >41 on eighteen-item subscales of psychological distress in the Brief Job Stress Questionnaire were randomly assigned to receive a tablet containing HK L-137 (10 mg) or a placebo tablet daily for 12 weeks. The URTI symptoms were rated once daily on the validated twenty-one-item Wisconsin Upper Respiratory Symptom Survey-21. Immune functions, such as concanavalin A-induced proliferation and percentages of interferon (IFN)-γ- and IL-4-producing CD4 T cells of peripheral blood mononuclear cells (PBMC), and serum IFN-β concentrations were measured every 4 weeks. URTI incidence was significantly lower in the HK L-137 group than in the control group. URTI incidence, duration and severity, and duration of medication showed significant negative correlations with duration of HK L-137 intake. The percentage change from baseline of concanavalin A-induced proliferation of PBMC was significantly greater in the HK L-137 group than in the control group. These findings suggest that daily HK L-137 intake can decrease URTI incidence in healthy subjects, possibly through augmentation of immune functions.
authors.affiliation: Research and Development Institute, House Wellness Foods Corp. , Itami , Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Hirose
authors.affiliation: Research and Development Institute, House Wellness Foods Corp. , Itami , Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yamamoto
authors.affiliation: Research Center for Infectious Diseases , Medical Institute of Bioregulation, Kyushu University , Kyushu , Japan.
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Yoshikai
authors.affiliation: Research and Development Institute, House Wellness Foods Corp. , Itami , Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Murosaki
keywords: Con A, concanavalin A; HK L-137, heat-killed Lactobacillus plantarum L-137; IFN, interferon; Immune function; Lactobacillus plantarum; PBMC, peripheral blood mononuclear cells; Stress; Th, T helper; URTI, upper respiratory tract infection; Upper respiratory tract infections; WURSS, Wisconsin Upper Respiratory Symptom Survey; WURSS-21, short-form Wisconsin Upper Respiratory Symptom Survey; WURSS-44, long-form Wisconsin Upper Respiratory Symptom Survey; Wisconsin Upper Respiratory Symptom Survey