Question

why is self-reactivity of t cells bad? I need a detailed explanation please.

Answer 1

A healthy adaptive imune system respond to foreign antigen but remain tolarent to self. During lymphocyte development the autoreactive clones are eliminated. T cell development occurs in Thymus. During develoment process based on the T-cell reecptor, functional T-cell are selected ( positive selection) whereas T cell that are autoreactive is eliminated ( negative seleciton ). But thymic selection process is not completely perfect and as a result autoreactive/ self reactve T cells can release into periphery very frequently. Such autoreactive/ self reactive T cell are very dengarous to host body as they can initiate autoimmune response , it become active against body's own immune system. In this situation the immune system can not differentiate between foreign antigen and healthy cells or tissue of body and create autoantibodies to destroy own healthy tissue. This ultimately generates autoimmune diseases. Some examples of these celiac disease, diabetes mellitus type 1,Graves' disease, rheumatoid arthritis, multiple sclerosis