Lactobacillus helveticus LH76 safely increases IgM and C3, enriches Blautia and Bifidobacterium in healthy adults

Probiotics are increasingly recognized for their potential to modulate host immunity via the gut microbiota. However, the immunomodulatory effects are strain-specific, not a universal class property, necessitating comprehensive characterization of individual strains. Lactobacillus helveticus LH76 is a promising candidate, but its safety profile and specific functional effects on human immunity and gut microbiota have not been fully established, representing a critical gap for its therapeutic application. This study aimed to systematically evaluate LH76's safety and its impact on immune biomarkers and gut microbiota composition.

Researchers conducted a multi-faceted study, beginning with a preclinical safety assessment of Lactobacillus helveticus LH76. This included whole-genome sequencing for antibiotic resistance and virulence genes, in vitro assays for hemolysis, biogenic amine production, and cytotoxicity in Caco-2 cells. An acute oral toxicity study in mice was also performed. Subsequently, an 8-week randomized, double-blind, placebo-controlled trial was conducted in healthy adults. Participants received LH76 3 × 10¹⁰ CFU/day or placebo. Primary endpoints included safety (hematological, biochemical, metabolic parameters) and immune-related biomarkers (IgA, IgM, IgG, C3, C4, LL-37, calprotectin), alongside gut microbiota composition via 16S rRNA sequencing.

Preclinical safety assessments demonstrated a favorable profile for LH76. Genomic analysis revealed no detectable antibiotic resistance or classical virulence genes. In vitro, LH76 exhibited no hemolytic activity, negligible biogenic amine production, and no cytotoxicity in Caco-2 cells. In vivo, the acute oral toxicity study in mice showed no adverse effects or pathological abnormalities, with an LD50 exceeding 2 × 10¹⁰ CFU/kg. In the clinical trial, LH76 was well tolerated, with no adverse changes in hematological, biochemical, or metabolic parameters compared to placebo. > LH76 supplementation significantly increased serum IgM and C3 levels, while decreasing C4 and LL-37 levels, indicating specific immunomodulatory effects. Furthermore, the intervention group showed increased microbial richness and relative enrichment of beneficial genera, including Blautia and Bifidobacterium. PICRUSt2-based analysis also suggested shifts in predicted microbial metabolic pathways, though these findings were noted as inferential.