Which type of cell helps to activate T cells during an immune response?

Antigen-presenting cells (APCs) play a critical role in activating T cells during an immune response. These specialized cells, which include dendritic cells, macrophages, and B cells, capture and process antigens from pathogens. Once they have processed an antigen, APCs present the antigenic fragments on their surface in conjunction with major histocompatibility complex (MHC) molecules. This presentation is essential for the recognition of the antigen by T cells.

When a T cell encounters an APC displaying the appropriate antigen-MHC complex, it becomes activated and can proliferate and differentiate into effector T cells. The direct interaction between the APC and T cell, along with co-stimulatory signals provided by the APC, is crucial for a robust immune response. This activation process allows T cells to effectively respond to infections and coordinate the overall immune response against pathogens.

In contrast, Memory B cells provide long-term immunity by retaining information about past infections, Plasma cells are involved in producing antibodies, and Cytotoxic T cells are responsible for killing infected cells directly. While these cells have important functions in the immune response, it is specifically the antigen-presenting cells that are pivotal in activating T cells.