Question

Many cells in the human body have proteins on the surface that are able to interact with the receptors of helper T cells. Explain the mechanisms and why it is that such an interaction or signal does not usually result in an autoimmune reaction?  

Answer 1

The T-cell receptor molecule is embedded in the membrane of the cell, and a portion of the molecule extends away from the cell surface into the area surrounding the cell. The chains each contain two folded domains, one constant and one variable, an arrangement similar to that of the chains of antibody molecules. And, as is true of antibody structure, the variable domains of the chains form an antigen-binding site. However, the T-cell receptor has only one antigen-binding site, unlike the basic antibody molecule, which has two.

Many similarities exist between the structures of antibodies and those of T-cell receptors. Therefore, it is not surprising that the organization of genes that encode the T-cell receptor chains is similar to that of immunoglobulin genes. Similarities also exist between the mechanisms B cells use to generate antibody diversity and those used by T cells to create T-cell diversity. These commonalities suggest that both systems evolved from a more primitive and simpler recognition system.

They not only help activate B cells to secrete antibodies and macrophages to ... we discuss the multiple signals that help activate a T cell and how a helper T cell, ... are recognized by the co-receptor protein CD28 on the surface of the T cell. ... This is one mechanism by which a T cell can become tolerant to self antigens.