Infection and Immunity

What is a primary immune response?

The first time an antigen is encountered. After 7-10 days, there is an antibody response.

What is a secondary immune response?

An encounter with a previously encountered antigen. Memory lymphocytes allow for a faster and stronger response.

What is the structure of an antibody?

They have two light chains and two heavy chains which are held together by inter-chain disulphide bonds. There are two antigen binding sites (Fab) and one effector function controlling region (Fc).

What is the primary response in type one hypersensitivity?

An allergen enters the body and is taken up by a dendritic cell which then expresses a peptide on an MHC molecule. This migrates to the lymph nodes where T cells will activate and proliferate into Th2 cells through the release of IL-4. Th2 cells activate B cells, these leave the lymph nodes to travel toward the allergen entry point. The Th2 cell produces cytokines that instruct the B cell to make IgE.

What is the secondary response in type one hypersensitivity?

Allergen enters the body and is bound to mast cells with IgE, activating the mast cell. These mast cells release pre formed granules (histamine) and newly formed granules (cytokines) which contribute to the tissue specific response.

Immunological tolerance

Ensures that the immune system does not react against the body’s own tissues and cells (self antigens).

Clonal deletion - central tolerance

Prevents the body from generating lymphocytes that recognize self antigen. This occurs in the bone marrow (B cells) and the thymus (T cells).

Anergy - peripheral tolerance

Some self reactive lymphocytes will escape from central tolerance into the periphery. Dendritic cells presenting self peptide will bind to autoreactive T cells and inactivate them.

Suppression - peripheral tolerance

Some cells that do not die in central tolerance will develop into Treg cells. These can inhibit activation of autoreactive lymphocytes.

Ignorance - tolerance

Antigens contained in privileged regions (eyes) are released and activate autoreactive lymphocytes.

Positive selection of T cells during central tolerance

T cell receptors are judged on their affinity for self MHC molecules. If there is no affinity, they undergo death.

Negative selection of T cells in central tolerance

Tests the affinity of the T cell receptor for self antigen. If they react too strongly they undergo apoptosis.

How are B cells educated in central tolerance

Newly rearranged B cell receptors are tested against self antigen, if they react too strongly they undergo apoptosis.

What are the four requirements for autoimmune disease

1. Escape of autoreactive clones from central tolerance

2. Autoreactive clones encounter self antigens

3. Peripheral tolerance failure

4. Autoreactive tissue damage

What type of autoimmune disease results from type II and III HS

Type II HS results in organ specific autoimmune diseases.

Type III HS results in systemic autoimmune diseases.