Question

How do T cells recognize and respond to foreign antigen? What types of cells are responsible for helping with this process?

Answer 1

In order to recognize a foreign antigen, T cells must bind their TCR receptor to a short sequence of amino acids called antigen. However, the pathogen must be phagocyted, processed and presented by the antigen presenting cells (APC). The main type of APC are the dendritic cells. They phagocyte the pathogen, degrade it into small fragments and one of those fragments is the antigen which will be presented by the major histocompatibility complex (MHC) of the APC on its surface.

Once the antigen is presented by the MHC, the T cell receptor (TCR) on the surface of the T cell will bind to the complex MHC-antigen. Depending on the nature of the antigen, the T cell will promote a determined immunological response.