A Review of Immunomodulatory Properties of Paraprobiotics and Their Mechanisms

Abstract:: Paraprobiotics, non-viable microbial cells or their components, are attracting interest as a safer alternative to live probiotics for immune support. This narrative review synthesizes evidence on (i) preparation methods of paraprobiotics (thermal, high-pressure, irradiation/UV, ohmic heating), (ii) mechanistic links between microbe-associated molecular patterns and host pattern-recognition receptors, and (iii) functional outcomes across in vitro, animal, and early human studies. Preparation methods influence biological activity: conditions that preserve or expose key surface structures (S-layer proteins, lipoteichoic acids, peptidoglycans, β-glucans) modulate molecular and immune signaling and cytokine profiles. Paraprobiotics frequently increased macrophage phagocytosis and nitric oxide production, altered pro- and anti-inflammatory cytokines, improved epithelial barrier markers, and enhanced resistance to pathogens. Several research gaps remain, including limited mechanistic studies, inconsistent reporting of processing kinetics and cell integrity, nonstandard dose units, and variability in immune responses. The literature indicates that pattern recognition receptor- mediated immunomodulation by paraprobiotics requires further rigorous investigation. Overall, this review underscores paraprobiotics as a safe and promising adjunct for modulating immune function, particularly for immunocompromised individuals and for use in food-based applications.