What is costimulation and what is its function?

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What is costimulation and what is its function?

Costimulation is the extra signal T cells need beyond their TCR recognizing antigen presented by MHC. This second signal comes from interactions between costimulatory molecules on antigen-presenting cells (like B7/CD80-86) and receptors on T cells (like CD28). It serves to confirm that the antigen encounter happened in the right context and provides survival and growth signals (such as promoting IL-2 production and receptor expression) so the T cell can proliferate and differentiate into an effector cell. If a T cell receives only the TCR signal without this second signal, it becomes anergic or undergoes deletion, leading to tolerance and helping prevent autoimmunity. So the function of costimulation is to determine whether activation occurs and to support a productive immune response in the appropriate context. The idea that costimulation promotes tolerance without activating T cells reflects what happens in the absence of costimulation, not when costimulation is present.

Costimulation is the extra signal T cells need beyond their TCR recognizing antigen presented by MHC. This second signal comes from interactions between costimulatory molecules on antigen-presenting cells (like B7/CD80-86) and receptors on T cells (like CD28). It serves to confirm that the antigen encounter happened in the right context and provides survival and growth signals (such as promoting IL-2 production and receptor expression) so the T cell can proliferate and differentiate into an effector cell.

If a T cell receives only the TCR signal without this second signal, it becomes anergic or undergoes deletion, leading to tolerance and helping prevent autoimmunity. So the function of costimulation is to determine whether activation occurs and to support a productive immune response in the appropriate context. The idea that costimulation promotes tolerance without activating T cells reflects what happens in the absence of costimulation, not when costimulation is present.

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