what is antigen presentation?Watch
Antigen presentation is a process in the body's immune system by which macrophages, dendritic cells and other cell types capture antigens, then enable their recognition by T-cells. The basis of adaptive immunity lies in the capacity of immune cells to distinguish between the body's own cells and infectious pathogens. The host's cells express "self" antigens that identify them as such. These antigens are different from those in bacteria ("non-self" antigens) or in virally-infected host cells ("missing-self"). The ability of the adaptive immune system to survey for infection requires specialized pathways of enabling recognition of pathogen-derived antigens by T cells.
Source: Boundless. “Antigen-Presenting Cells.” Boundless Anatomy and Physiology. Boundless, 27 Jun. 2014. Retrieved 18 Feb. 2015 from https://www.boundless.com/physiology...ells-979-8495/
In order for our immune system to protect us, it needs to recognise foreign matter. T cells particularly depend on this but they are at the end of antigen presentation and the stage after (presentation is the recognition stage, once recognised as foreign we need to get rid of it). Antigen presentation itself is a cell recognising a foreign protein, breaking it down to its constituent parts (peptides) [a protein is lots of amino acids in a chain, a peptide is a small chain of amino acids] and presenting these foreign parts on its surface bound to MHC receptors so T cells can recognise these invaders and deal with them.