Video Transcript
Which of the following correctly
compares the primary response and secondary response to a pathogen? (A) The primary response to a
pathogen is typically slower and produces a smaller volume of antibodies than the
secondary immune response. (B) The primary response to a
pathogen is typically faster and produces a larger volume of antibodies than the
secondary immune response. (C) The primary and secondary
immune responses produce the same volume of antibodies in the same amount of
time.
This question asks us to compare
the primary and secondary responses of the acquired immune system. Lymphocytes, like T cells and B
cells, are part of the adaptive immune system. These cells recognize antigens on
the surface of pathogens and mount an immune response to clear the infection. B cells can become activated in
response to recognizing of antigen and divide and differentiate into plasma
cells. Plasma cells can secrete antibodies
to combat the pathogen.
Here’s a graph that shows the
amount of antibody produced over time after being exposed to a pathogen. Let’s first discuss this primary
immune response and then see what happens during a repeat exposure of the pathogen
in a secondary immune response. The primary immune response occurs
when an antigen is recognized for the very first time. This is usually a slow recognition
process because the adaptive immune system doesn’t immediately recognize the
antigen.
Once a B cell develops that can
recognize this particular antigen, the B cell can become activated. Activated B cells can divide and
differentiate into memory B cells and plasma cells. Plasma cells can secrete antibodies
that are specific for the pathogen. This is what causes the amount of
antibody to increase during the primary immune response.
Once the infection is cleared,
these plasma cells are deactivated and die, and antibody levels begin to fall. What’s left are the memory B
cells. These cells are long-lasting and
specific for the antigen that triggered their development. So if the pathogen reinfects the
host, then these memory B cells can immediately recognize it. This memory cell can then divide
and form plasma cells that can secrete high levels of antibody against this pathogen
quickly. So when we look at the secondary
immune response, we see that antibody levels rise very quickly and there’s much more
of them compared to the primary immune response.
Therefore, the correct answer is
(A). The primary response to a pathogen
is typically slower and produces a smaller volume of antibodies than the secondary
immune response.
