Costimulatory molecules are essential proteins found on the surface of antigen-presenting cells (APCs) that provide a second signal necessary for T cell activation and function. This second signal is critical in the immune response, ensuring that T cells are fully activated only when there is a legitimate threat, such as an infection. The interaction between costimulatory molecules on APCs and their receptors on T cells helps to amplify the immune response and maintain tolerance to self-antigens, connecting the innate and adaptive immune systems.
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