How does the immune system distinguish between self and non-self particles?

The immune system distinguishes between self and non-self particles primarily through the action of major histocompatibility complex (MHC) molecules. These molecules are essential for the recognition of antigens by T cells, which are key players in the adaptive immune response. MHC molecules present peptide fragments derived from proteins within cells, highlighting either self-proteins or foreign antigens.

When MHC molecules display self-peptides, T cells that recognize these complexes typically receive signals to remain tolerant and are not activated, preventing an autoimmune response. Conversely, when MHC molecules present non-self peptides—such as those from pathogens—T cells can recognize these as foreign, prompting an immune response to eliminate the invaders. This system is critical for maintaining immunity while preventing the immune system from attacking the body’s own tissues.

Antibodies do play a role in identifying and neutralizing pathogens, but they are not responsible for the initial distinction between self and non-self. Cytokines are signaling molecules that mediate and regulate immune responses but do not inherently provide the self/non-self discrimination. Memory cells are important for the rapid response upon re-exposure to previously encountered pathogens, but they do not function in the initial recognition of self versus non-self; rather, they come into