Lactococcus lactis, a lactic acid bacterium commonly used in dairy fermentation, has been investigated for its potential immunomodulatory effects, which may be beneficial for respiratory allergies such as allergic rhinitis or asthma. The rationale for its use is based on the concept that certain probiotic strains can help modulate the gut-associated lymphoid tissue (GALT) and, in turn, influence systemic immune responses, potentially reducing allergic inflammation.

Several preclinical studies (in vitro and animal models) have demonstrated that strains of L. lactis can alter cytokine production, promote regulatory T cell responses, and reduce markers of allergic inflammation. For example, some research in mouse models of allergic airway inflammation has shown that orally administered L. lactis can attenuate eosinophil infiltration and decrease Th2 cytokines (such as IL-4 and IL-5), which are key drivers of allergic responses.

Human clinical evidence, however, is limited. A few small pilot studies and clinical trials using L. lactis or products containing it (sometimes in combination with other probiotics) suggest potential benefits in reducing symptoms of allergic rhinitis or improving quality of life, but results are not always consistent and sample sizes are small. The exact mechanisms and strain-specific effects require further elucidation.

In conclusion, while there is emerging scientific evidence—mostly from animal studies and a few preliminary human trials—supporting the use of L. lactis for respiratory allergies, the overall evidence is still considered preliminary (rated 2/5), with a need for more robust, large-scale clinical research.