How does the body recognize foreign antigens?

The body recognizes foreign antigens primarily through receptors on immune cells, such as T cells and B cells. These immune cells possess specific receptors that bind to distinct molecular structures present on antigens, which are often proteins or polysaccharides found on the surface of pathogens.

When B cells encounter an antigen, their unique membrane-bound antibodies can directly bind to it, which may lead to their activation and subsequent antibody production. T cells, particularly, have T-cell receptors (TCRs) that recognize processed antigens presented by Major Histocompatibility Complex (MHC) molecules on the surface of antigen-presenting cells. This receptor-mediated recognition is crucial for the immune system's ability to differentiate between self and non-self, thereby initiating an appropriate immune response.

While antibody production is a consequence of immune recognition, it is the receptors on T and B cells that facilitate the initial recognition of antigens. Memory cells do play a significant role in the immune response by providing long-lasting protection against previously encountered antigens, and phagocytizing pathogens is a mechanism of pathogen elimination rather than initial recognition. Nevertheless, the primary method of antigen recognition occurs through these specific receptors on immune cells.