Question

Why does MBL not bind to our own cells (even though some of our cells will have mannose on the outside)?

a) Lack of thioester bonds
b) Presence of self-inhibitory factors
c) Immune tolerance mechanisms
d) Exclusively binds to mannose-deficient cells

Answer 1

MBL does not bind to our own cells due to the presence of self-inhibitory factors that prevent an autoimmune response. Self-cells express MHC I molecules that allow the immune system to recognize them and prevent autoimmunity, as seen in the interaction between CTLs and APCs.

Step-by-step explanation:

Mannose-binding lectin (MBL) is a component of the immune system that recognizes specific carbohydrate patterns found on the surface of many pathogens. MBL does not bind to our own cells despite the presence of mannose because of the presence of self-inhibitory factors. Our cells express these inhibitory substances, which prevent MBL from mistakenly targeting them as foreign. This is similar to how the body employs immune tolerance mechanisms to distinguish between self and non-self entities, preventing autoimmune responses.

Furthermore, all nucleated cells possess MHC I molecules which present self-antigens to the immune system, contributing to the ability of the immune cells to recognize self-cells and prevent autoimmunity. This recognition process is vital for the proper functioning of the immune response, such as when cytotoxic T lymphocytes (CTLs) use their CD8 coreceptors to bind MHC I molecules on antigen-presenting cells (APCs).