What Is a Superantigen?

Super antigen (SAg) is a kind of substance that can activate a large number of T cell clones with extremely low concentration (10-9M) and produce a strong immune response. Compared with common antigens, superantigens do not require conventional intracellular antigen presentation and are not MHC-restricted. One end of the superantigen binds to the non-polymorphic region outside the MHC- molecular antigen binding groove on the surface of the APC, and one end binds to the V outer region of TCR. By these two types of binding, T cells are activated.

Basic Information

Chinese name

Superantigen

Foreign name

superantigen, SAg

Classification

Exogenous superantigen

Advantages

Involved in certain pathological processes

Superantigen classification

SAg is a class of polyclonal activators. At present, superantigens can be divided into T-cell superantigens and B-cell superantigens according to the activated cells, and T and B-cell superantigens are divided into endogenous super (viral) antigens and exogenous according to their sources. (Bacterial type) superantigen. Such as S. aureus enterotoxin and group A streptococcus M protein can activate T cells belonging to the exogenous T cell superantigen. Viral DNA is integrated into host cell DNA to produce endogenous superantigens. For example, after the mouse breast tumor virus invades lymphocytes, the expressed viral protein products and human immunodeficiency virus expression products in the body can become endogenous. T cell superantigen. Staphylococcus aureus A protein is an exogenous B-cell superantigen, and the human immunodeficiency virus gpl20 can also bind certain subtypes of B cells and is an endogenous B-cell superantigen.

Superantigen mechanism

1. Immune activation Superantigens can activate T cells and antigen presenting cells. Activated cells produce a large number of cytokines, causing sequential activation of macrophages and other immune cells to show immune effects. Superantigen has potential application value for the research of anti-tumor drugs. In addition, the production of a large number of cytokines can cause fever, weight loss, osmotic pressure imbalance, etc., and participate in a variety of bacterial food poisoning, certain types of shock, AIDS And other diseases.

2. Immunosuppressive effect Under the stimulation of superantigen, T cells are over-activated and depleted, resulting in an imbalance in the function and number of T cells and a secondary immunosuppressive state.

3. Induced immune tolerance. Some endogenous superantigens may act on thymus cells, and the superantigen-responsive cells are cleared by clonal selection to establish an immune tolerance state.

Clinical significance of superantigen

1. Superantigen-induced immune suppression and immune tolerance

Superantigen over-activates a large number of T cells, and clones are cleared by activating cell apoptosis. Restimulation of the same antigen does not cause proliferation, which results in immune tolerance.

2. Anti-tumor prospects of superantigens

Superantigens release a large number of cytokines by activating polyclonal T cells, which has a significant killing effect on tumor cells. Therefore, superantigen has the potential to become a new generation of antitumor agents.

3. Superantigen and disease

Superantigens are related to the occurrence of toxic shock syndrome, Kawasaki disease (also known as cutaneous mucosal lymph node syndrome), various bacterial food poisonings, and psoriasis.