Microbiology Practice Exam 2026 – Comprehensive All-in-One Guide for Exam Success!

The activation of the cell-mediated response of the immune system primarily involves antigen presenting cells (APCs). APCs, which include dendritic cells, macrophages, and B cells, play a crucial role in capturing, processing, and presenting antigens to T-cells. When these cells encounter an antigen, they engulf it, break it down, and then display peptide fragments of that antigen on their surface bound to major histocompatibility complex (MHC) molecules.

When a T-cell recognizes its specific antigen presented by an APC via the T-cell receptor (TCR), this interaction is critical for the activation of the T-cell. The activation of these T-cells leads to a cascade of immune responses, including the differentiation of T-cells into various subsets such as cytotoxic T-cells, which are essential for directly attacking infected cells and coordinating the overall immune response.

While T-cells are essential for carrying out the cell-mediated immune response, they cannot become activated without the prior action of APCs. Therefore, the correct choice highlights the pivotal role that antigen presenting cells have in initiating and regulating this critical component of the immune system.