Video Transcript
Most of our own body cells have
antigens on their surface. Why does the humoral immune
response usually not end up attacking our own body cells? (A) Our immune system can
distinguish between self- and non-self-antigens. (B) Harmful body cells are removed
by the nonspecific immune system, for instance, through sneezing or coughing. (C) Our body cells do not contain
the genes that can produce the MHC molecules which present the antigens on the cell
surface. Or (D) this is incorrect; in the
vast majority of cases, our immune system does attack our own body cells.
Let’s remove the answer options for
now and remind ourselves of how the immune system deals with the antigens that are
present on the surface of our own body cells. All body cells that have a nucleus
contain genes in their DNA which code for major histocompatibility complex
molecules, or MHCs for short. Even when the body is not infected
with a pathogen, body cells are presenting antigens via these MHC molecules on their
cell surface. But rather than the antigens being
derived from a pathogen, they are derived from harmless intracellular host
proteins. This type of antigen is called a
self-antigen.
By contrast, if a body cell is
infected, for example, with a virus, and is presenting a viral antigen on its MHC
molecules, this is known as a non-self-antigen. During the humoral immune response,
B cells are activated and release antibodies, which target non-self-antigens,
leading to the destruction of infected cells.
So why is it that B cells do not
target self-antigens too? The answer is that they undergo a
process called B cell tolerance, primarily while they are maturing in the bone
marrow. During B cell tolerance, B cells
are exposed to self-antigens. If any B cells possess B cell
receptors which recognize and bind to a self-antigen, they are destroyed. This ensures that only B cells
which recognize non-self-, foreign antigens will reach full maturation and migrate
to the periphery.
It is important to note that B cell
tolerance is not perfect, and sometimes B cells which recognize self-antigens will
survive. If this happens, it can lead to
autoimmune disorders, such as lupus. We now have enough information to
answer the question. The correct answer is (A). The humoral immune response does
not usually attack our own body cells because our immune system can distinguish
between self- and non-self-antigens.
