Streptococcus Thermophilus for Immune Function

Research suggests that the evidence linking Streptococcus thermophilus specifically to immune function benefits in humans is limited and mixed. The most directly relevant human trial — a randomized crossover study from 1997 — found no significant improvements in immune markers when adults with allergic histories consumed yogurt containing S. thermophilus and Lactobacillus bulgaricus compared to plain milk. More supportive signals come from a large randomized trial (the ProPrems trial) examining a three-strain probiotic combination that included S. thermophilus in very preterm infants, though that publication described methodology rather than outcomes, and any observed effects cannot be attributed to S. thermophilus alone. Laboratory and non-human research offers some additional context — one study found that S. thermophilus, among other probiotic strains, could stimulate lactoferrin production in bovine mammary cells, and a separate study found that a multi-strain probiotic combination shifted immune signaling markers toward a Th2 profile — but these findings involve mixed probiotic consortia, non-human models, and vary considerably in design and relevance, making it difficult to draw firm conclusions about S. thermophilus as an isolated immune-supporting agent in humans.