T Cell Activation via Antigen Presentation

T cell activation via antigen presentation is a fundamental process in adaptive immunity, where T cells are primed to respond to pathogens or abnormal cells. This process requires the interaction between T cell receptors (TCRs) and antigens presented by major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells (APCs), along with additional costimulatory signals. Key components include APCs (dendritic cells, macrophages, B cells), MHC Class I and II molecules, TCR recognition, and costimulatory signals (CD28/B7, LFA-1/ICAM-1, CD40/CD40L). Activation involves antigen recognition (signal one), costimulation (signal two), immunological synapse formation, and intracellular signaling cascades. Outcomes include clonal expansion, cytokine secretion, and target cell killing. Failure in proper signaling can result in immune deficiency or autoimmunity; manipulation forms a basis for immunotherapies.

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