Role of immunobiotic lactic acid bacteria as vaccine adjuvants

Probiotic bacteria are the bacteria that impart health benefits to the host when consumed in adequate quantities. Among these, lactic acid bacteria (LAB) are the most well-recognized group of bacteria that have the required safety attributes and are widely used with numerous health benefits. However, one of the recognized characteristics of these beneficial bacteria is the ability to regulate the mucosal immune system by stimulating the antigen-presenting cells such as dendritic cells. These immune-modulating functions of probiotics are referred to as Immunobiotics and the bacteria possessing these abilities are termed as immunobiotic probiotics. The immunobiotic LAB is associated with the upregulation of both innate and adaptive immune responses and consequently provides health benefits to the host by boosting their immune response against a number of bacterial and viral infections. In the past decade, the enormous role of immunobiotic LAB in vaccine development has been well emphasized. The immunobiotic probiotic LAB and their produced metabolites are known to have functions similar to adjuvants. In vaccinology, the term adjuvant represents the substance that when added to a vaccine could boost the immune response to the antigens carried in that vaccine. To date, a number of adjuvants are being used in conventional vaccines that are being utilized throughout the world. Although these adjuvants have well-established safety records yet with the reports of some side effects arising due to these substances, the need for more efficacious and safe adjuvants has been heavily felt. In this review, we discuss some essential properties of immunobiotic probiotic LAB that has shown adjuvant potential especially in upregulating the mucosal immune response.