Autoimmune disorders result from T cells that: A) fail to recognize MHC proteins on cell membranes. B) produce alternate T cell receptors (TCRs) while circulating in the bloodstream. C) are activated by major histocompatibility complex (MHC) molecules displaying self antigens. D) fail to produce TCRs.
C) Autoimmune disorders occur when self-reactive T cells become activated by MHC molecules presenting self antigens, leading to an immune attack on the body’s own tissues. Normally, central and peripheral tolerance mechanisms prevent these T cells from activating.
What this question is really testing
You are being asked what goes wrong in immune tolerance. Autoimmunity happens when T cells that should be eliminated or silenced instead respond to the body’s own (self) antigens.
Why choice C matches autoimmunity
T cells recognize antigen only when it is presented on an MHC molecule. If a T cell with a self-reactive TCR is activated by an MHC molecule displaying a self peptide, it can trigger inflammation and tissue damage, which is the basis of autoimmune disease.
Why the other choices are wrong
- A) If T cells fail to recognize MHC, they generally cannot be properly activated, which would cause immunodeficiency, not autoimmunity.
- B) TCR gene rearrangement happens during T cell development in the thymus, not “while circulating” in the blood.
- D) If T cells fail to produce TCRs, they cannot recognize antigen at all, which again points to immunodeficiency rather than autoimmunity.
Quick memory cue
Autoimmunity = failure of tolerance to self antigen presented on MHC.
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