Final answer:
Gut microbiota modulates the host immune system by promoting both pro-inflammatory and anti-inflammatory responses, contributing to immune defense, metabolic processes, and preventing harmful bacteria from establishing infections.
Step-by-step explanation:
The impact of gut microbiota on the host immune system is multifaceted. The correct answer to the question is D) Gut microbiota modulates the immune system, influencing both pro-inflammatory and anti-inflammatory responses. The gut microbiota plays a protective, immunomodulatory, metabolic, and trophic role in the host. For example, gut microbes produce anti-inflammatory factors and vitamins, while also deterring the attachment and growth of harmful bacteria. Additionally, the interaction between commensal bacteria and the host includes communication with the mucosal immune system which can activate immune responses and influence the development of allergies and other autoimmune diseases. The microbiota contributes to 'colonization resistance,' preventing pathogen invasion, and can influence the severity of infections. Antibiotics can disrupt the natural balance of the gut microbiome, underscoring the importance of these microbes in maintaining immune health.