Final answer:
The immune system distinguishes between self and non-self antigens using MHC molecules. Self antigens are presented by these complexes on one's own cell surfaces, while non-self antigens, which are foreign, trigger an immune response. MHC class I and II molecules are pivotal in the presentation of antigens to T cells for immune activation.
Step-by-step explanation:
The difference between self and non-self antigens lies in the immune system's recognition of molecular structures on cell surfaces. Self antigens are the individual's own molecules, typically presented by major histocompatibility complex (MHC) molecules on cell surfaces, allowing immune cells to recognize them as part of the body's normal constituents. Non-self antigens, however, are recognized as foreign, triggering an immune response. Major histocompatibility complexes, including MHC class I and class II molecules, play crucial roles in the immune system.
MHC class I molecules are found on virtually all nucleated cells and present normal self-antigens as well as abnormal or non-self pathogens to T cells, critical for cellular immunity. MHC class II molecules, on the other hand, are found only on specific immune cells like macrophages, dendritic cells, and B cells. They present non-self pathogen antigens to T cells, leading to the initial activation of the immune response. This system of antigen presentation is vital for the identification and destruction of pathogens, as well as for the prevention of autoimmune responses where the body might otherwise attack its own cells.