Video Transcript
The binding of a T-helper cell to
an antigen on an antigen-presenting cell activates the T-helper cell to rapidly form
clones of itself by mitosis. Which of the following is not a
correct description of what these cloned T cells can do? (A) They can develop into memory
cells that remain in the bodily fluid for a long time after the first infection. (B) They can stimulate B cells to
divide and release their antibodies. (C) They can stimulate phagocytes
to carry out phagocytosis. (D) They can activate cytotoxic T
cells to kill body cells infected by pathogens. Or (E) they can differentiate into
histamine-producing cells and help regulate the inflammatory response.
Let’s remove the answer options for
now and remind ourselves of the different roles activated T-helper cells can
play.
Activated T-helper cells will have
different roles depending on where they are activated and what chemical signals they
receive. As their name suggests, the primary
role of activated T-helper cell clones is to help activate other cells of the immune
system. If the T cell receptor of a T cell
clone recognizes its complementary MHC–antigen complex on a B cell, it will provide
signals to activate the B cell. The activated B cell will then
differentiate into a plasma cell which will release antibodies to fight the
infection.
Through a similar interaction
between a T cell receptor and an MHC–antigen complex, T cell clones can also
activate phagocytes such as macrophages. Activated phagocytes will carry out
phagocytosis where they engulf and digest extracellular pathogens. In addition, an activated T-helper
cell clone can help to activate a cytotoxic T cell. It does this indirectly by
interacting with a specific type of antigen-presenting cell called a dendritic
cell. When the dendritic cell then
interacts with the cytotoxic T cell through its MHC–antigen complex, it releases
cytokines which fully activate the cytotoxic T cell.
Activated cytotoxic T cells will
target infected cells for destruction. Some of the activated T-helper cell
clones will differentiate into memory cells. Memory cells are long-lived cells
which remain in the body for many years after the infection has been cleared. This means that if we are infected
again in the future with the same pathogen, our memory cells can be activated to
mount a much quicker and more powerful immune response.
We can therefore deduce that (E) is
the correct answer to the question. Histamine is only produced by mast
cells and basophils as part of the nonspecific inflammatory response, and not by T
cells.