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==Mucosal tolerance==

==Mucosal tolerance==

Mucosal tolerance is the systemic unresponsiveness towards antigens administered across mucosal surfaces. The highest antigenic load of the body surfaces occurs in the GI tract, so mucosal tolerance is also sometimes referred to as oral tolerance. When oral tolerance towards food antigens breaks down, inflammatory responses are induced. [[Regional Lymphoid Tissue - Anatomy & Physiology|Gut associated lymphoid tissue]] is important in the development of oral tolerance: animals that lack Peyer’s patches and mesenteric lymph nodes do not develop oral tolerance. It is thought the liver and spleen may also play a role.

Mucosal tolerance is the systemic unresponsiveness towards antigens administered across mucosal surfaces. The highest antigenic load of the body surfaces occurs in the GI tract, so mucosal tolerance is also sometimes referred to as oral tolerance. When oral tolerance towards food antigens breaks down, inflammatory responses are induced. [[Regional Lymphoid Tissue - Anatomy & Physiology|Gut associated lymphoid tissue]] is important in the development of oral tolerance: animals that lack [[Peyer's Patches - Anatomy & Physiology|Peyer’s patches]] and mesenteric lymph nodes do not develop oral tolerance. It is thought the liver and spleen may also play a role.

In the GI tract, high doses of antigen can cause anergy or cell death. Low doses can induce a T cell response where the antigen is taken up and presented, inducing a Th2-like cell response which produces cytokines that suppress the Th1 inflammatory response, such as IL-10 and TGF-beta. Although the cellular response is antigen-specific, the cytokines released are not. TGF-beta is known to inhibit the proliferation and function of B-cells, cytotoxic T cells and NK cells. This means tolerance induction to one antigen suppresses an immune response to a second associated antigen - this mechanism has been used to suppress some autoimmune diseases by feeding with an antigen isolated from the affected tissue. This is known as '''bystander suppression'''.

In the GI tract, high doses of antigen can cause anergy or cell death. Low doses can induce a T cell response where the antigen is taken up and presented, inducing a Th2-like cell response which produces cytokines that suppress the Th1 inflammatory response, such as IL-10 and TGF-beta. Although the cellular response is antigen-specific, the cytokines released are not. TGF-beta is known to inhibit the proliferation and function of B-cells, cytotoxic T cells and NK cells. This means tolerance induction to one antigen suppresses an immune response to a second associated antigen - this mechanism has been used to suppress some autoimmune diseases by feeding with an antigen isolated from the affected tissue. This is known as '''bystander suppression'''.