What is the first step in the cell-mediated immune response?

The first step in the cell-mediated immune response involves naive T cells encountering antigens that are presented by antigen-presenting cells (APCs). This interaction is crucial because naive T cells must recognize specific antigens to become activated. APCs, such as dendritic cells, macrophages, and B cells, play an essential role by processing antigens and presenting them on their surface in conjunction with major histocompatibility complex (MHC) molecules.

When naive T cells bind to these antigen-MHC complexes, they receive necessary signals for activation, including co-stimulatory signals from the APCs. This process leads to the proliferation and differentiation of T cells into effector T cells, including cytotoxic T cells, which are specifically designed to target and destroy infected or cancerous cells.

This initial encounter is critical for ensuring that the immune response is tailored to the specific pathogen involved. The subsequent steps rely on this activation to mobilize the immune system effectively against the foreign invaders.