Immunology CH 10: The Mucosal Immune System

What is mucus composed of?

Mucins

What are mucins?

Glycosylated polypeptides that are crosslinked to form large, extended molecules

What type of cells produce mucus?

Goblet cells

Where is mucus produced?

in the mucosal epithelium

What is the first way mucus protects mucosal surfaces?

mucus physically impedes microorganisms

What is the second way mucus protects mucosal surfaces?

Mucus retains antibody and antimicrobial molecules W

What is the third way mucus protects mucosal surfaces?

mucus turns over every couple of days

Where are mucosal surfaces located?

mucosal surfaces line the body’s glands and internal tubes

Ex: the respiratory tract, gastrointestinal tract, and urogential tract

What secondary lymphoid tissues serve the small intestine?

The gut associated lymphoid tissues (GALT) and mesenteric lymphnodes

What does the GALT consist of?

Peyer’s patches and lymphoid follicles

Where are microfold cells (M cells) located?

In the epithelium directly underlying the Peyer’s patches and lymphoid follicles

What is the function of Microfold cells?

They transport microbial antigens from gut lumen to underlying lymphoid tissue to proactively activate immune responses

What type of immune responses do non mucosal tissues generate?

Reactive immune responses

Why do non mucosal tissues generate reactive immune responses?

They only have occasional contact with microbes so an immune response is generated only in the presence of an infection

Do non mucosal tissues reactive immune responses cause inflammation?

Yes because the tissue macrophages produce an inflammatory response that causes damage to host tissues.

What type of immune response do mucosal tissues generate?

A proactive immune response

Why do mucosal tissues generate a proactive immune response?

They have continuous contact with microbes so they have to be prepared for the barrier breach because it is much more likely to happen and happen fast.

What are plamsa cells and effector T cells doing in the gut lumen to prepare for a barrier breach of mucosal tissues?

Plasma cells are proactively producing antibodies against gut microbes

Effector T cells are ready and waiting for a breach to attack

Do mucosal tissues proactive immune response cause inflammation?

No because proactive immune responses are non inflammatory in nature

What are systemic tissue/non mucosal macrophages like?

They are phagocytic and they secrete inflammatory cytokines in response to PAMPs to generate an inflammatory response

What are mucosal tissue macrophages like?

They are phagocytic, but do not secrete inflammatory cytokines

Describe what dendrtic cells do in response to harmless food antigens in the gut:

In the gut, dendritic cells promote tolerance to food antigens by helping the immune system recognize harmless dietary proteins as non threatening rather than triggering an immune response

Describe how dendritic cells help the immune system recognize harmless dietary proteins as non threatening:

the dendritic cells capture the food antigens and travel to mesenteric lymph nodes where they then present the antigen and secrete anti inflammatory cytokines to activate anti inflammatory Tregs

What is oral tolerance?

when the immune system learns to ignore harmless proteins from food, preventing an unnecessary immune response.

Both the mucosal and systemic immune systems become unresponsive to these harmless microbes taken in by the mouth

What type of immune response is produced to microbes that have NOT breached the epithelial barrier and what type of cell promotes this response?

An anti inflammatory adaptive immune response is produced by mucosal dendrtic cells in the secondary lymphoid tissue.

Describe what is going on during an immune response to microbes that have not breached the epithelial barrier:

Dendritic cells are sampling commensal antigens from the gut lumen. The dendritic cells are staying in a tolerogenic state due to the guts anti inflammatory environment. Dendritic cells also activate T regs so they can suppress any inflammation. Effector T cells prepare for the chance of a breach. Plasma cells secrete IgA when neutralizes microbes and limit their contact with the gut lining.

What type of immune response is produced to a breach in the epithelial barrier?

An inflammatory response

Describe what happens if there is a breach in the epithelial barrier by a pathogen or opportunistic commensal microorganism:

In the case of a breach, epithelial cells will secrete inflammatory cytokines. This signals Tregs that it needs to allow the other effector T cells and other immune cells to let loose so they can clear the infection.

There is probably already a proactive adaptive immune response waiting to deal with the infection

Describe the roll that epithelial cells have in immune responses generated against microbial antigens:

In the presence of infection, epithelial cells secrete inflammatory cytokines which promote the proactive immune response to be generated

In the absence of infection, epithelial cells secrete anti inflammatory cytokines

What is celiac disease?

Pro inflammatory response to gluten is produced

(In someone who does not have celiac disease, Tregs and oral tolerance are produced in response to gluten)

What is chron’s disease?

Pro inflammatory response to commensal bacteria

(in someone without chron’s, the response to commensal bacteria is typically pro ANTI inflammatory)