AAMC 7, item 108 (Immune System)

[Dirtybird]

Hey,

So here's the question:

"Normally the immune system avoids attacking the tissues of its own body because:

A. a special intracellular process recognizes only foreign antigens
B. the body does not make any antigens that the immune system could recognize
C. it changes its antibodies to be specific ony to foreign antigens
D. it suppresses cells specific to the body's own antigens"

Correct answer is D. When doing this question, I thought all the statements were innacurate. I ended up choosing C because it seemed the least wrong at the time, but I totally know why its wrong. Why is D correct?

More specifically, what does it mean by suppressing cells? I thought the immune system suppressed itself with recognized antigens, but what does it mean by suppressing the cell expressing it? That made the answer seem like it was saying that the immune system would attack a cell containing antigens of the body.

I would appreciate if anybody could clarify this for me.

Thanks!

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[Arayh]

Humans are immunologically unresponsive to endogenous molecules because of self tolerance. Tolerance to self antigens is achieved by 3 processes: clonal deletion, clonal anergy and peripheral suppression. Clonal deletion refers to the selection pressures during B and T cell development where self-reactive/autoimmune B and T cells are destroyed after contact with self antigens. Clonal anergy refers to the loss of T and B cell functions after exposure to antigens in the absence of mandatory costimulatory signals. Peripheral suppression, occurs when cytotoxic T cells or macrophages secrete cytokines such as TGF Beta which downregulate the immune response.

All three processes can be considered suppressing self-responsive targeting/autoimmunity.

 

[sshah92]

Essentially the white blood cells (that are "matured" in the thymus) specific for antigens produced by our own body are destroyed. This basically happens through the processes mentioned above -- the maturation process in the thymus involves selecting for these antibodies specific to foreign antigens.

 

[Dirtybird]

Thanks guys, had no idea about that process