Question

Is it correct that the immune system does not necessarily eliminate bacteria in the gut, even though they have PAMPS on their surface?

a. The immune system eliminates all bacteria with PAMPS in the gut.
b. Gut bacteria, despite having PAMPS, are not necessarily harmful and are tolerated.
c. The immune system selectively targets harmful bacteria in the gut.
d. PAMPS trigger an innate immune response against all bacteria.

Is there information on oral tolerance, especially regarding how it avoids triggering the innate immune system despite PAMPS?
a. Oral tolerance mechanisms are well understood, including avoidance of innate immune activation.
b. Textbooks or references discussing oral tolerance and its relationship with PAMPS are limited.
c. Innate immune activation is an integral part of oral tolerance.
d. The avoidance of innate immune activation in oral tolerance is not fully explained.

Answer 1

The gut microbiome possesses PAMPs yet is tolerated by the immune system due to immune tolerance mechanisms involving regulatory T cells and specialized APCs that maintain mucosal homeostasis and prevent unwarranted immune responses.

Step-by-step explanation:

It is not correct to say that the immune system eliminates all bacteria with PAMPs in the gut. Instead, the gut harbors a complex microbiome composed of many bacterial species that, despite having Pathogen-Associated Molecular Patterns (PAMPs), are not harmful and are thus tolerated by the immune system. These bacteria play a crucial role in health, including aiding digestion and vitamin synthesis. The gut's mucosal immune system involves Mucosal Associated Lymphoid Tissue (MALT), such as Peyer's patches, that communicate with commensal bacteria to moderate immune responses and maintain homeostasis.

Immune tolerance is a key strategy utilized by the body to prevent unwanted immune responses to these harmless antigens. This is regulated in part by regulatory T (Treg) cells, which limit inflammation and prevent unnecessary immune activation. Tolerogenic dendritic cells are specialized antigen-presenting cells (APCs) that help in establishing oral tolerance, making it less likely for the immune system to attack harmless substances, including beneficial gut bacteria with PAMPs, thus preventing inappropriate inflammatory responses.