Antigen presentation is essential for the activation and clonal selection of what?

Antigen presentation is essential for the activation and clonal selection of T cells, particularly CD4+ helper T cells and CD8+ cytotoxic T cells. Antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells, process and present antigens on their surface using major histocompatibility complex (MHC) molecules. This interaction, along with co-stimulatory signals, initiates T cell activation, leading to proliferation and differentiation into effector cells. This process is crucial for the adaptive immune response against pathogens.