The intestinal mucosa represents a critical interface between the host immune system and intestinal commensals, harboring over 70% of peripheral lymphocytes. Here, we discuss the complex interactions between gut microbiota, intestinal barriers, and immune system dynamics, We explore how early-life microbial colonization shapes immune tolerance and how genetic and environmental factors modulate microbiota composition. Evidence from the literature reveals that specific bacterial species drive T cell differentiation, influencing immune responses through mechanisms including molecular mimicry and metabolite production. Gut microbiota not only regulates local intestinal immunity but also significantly impacts extraintestinal immune responses, potentially contributing to autoimmune diseases. By understanding the intricate relationship between commensal microorganisms and host immunity, we can understand the fundamental processes governing immune system development and potential pathogenic mechanisms