Video Transcript
Complete the sentence. Blank cells are involved in both
cell-mediated and humoral, antibody, responses.
The human immune system has two
complementary components: innate, also called nonspecific immunity, which fights
every pathogen in the same way, and specific, also called acquired or adaptive
immunity, which customizes a response based on the pathogen that needs to be
fought.
Cell-mediated responses and
humoral, also called antibody, responses are part of the specific immunity. The humoral immune response is
sometimes called B cell immunity or antibody immunity because it relies on the
action of B cells that make antibodies specific to the invading pathogen. These antibodies are released into
bodily fluids like the bloodstream and the lymph fluid. Humoral immunity is therefore
effective against extracellular pathogens, for example, viruses in the blood,
bacteria, or toxins produced by bacteria.
The cell-mediated immune response
is sometimes called T cell immunity because it relies on the action of cytotoxic T
cells. Cytotoxic T cells can find and
destroy abnormal and infected cells of the body. Cell-mediated immune responses are
therefore effective against intracellular pathogens, for example, host cells
infected by a virus. Note that although they are often
described separately, cell-mediated and humoral immune responses occur
simultaneously and interact closely with each other to fight infections.
So let’s have a look at what
happens after a pathogen has infected our body to find the name of the cells which
are involved in both specific immune responses. When a pathogen enters the body, it
is usually found in the bloodstream or lymph fluid. And it either infects a cell or is
engulfed by a specialized immune cell like a macrophage. Pathogens contain molecules or
proteins that are foreign from the molecules and proteins found within our body. These molecules and proteins are
generally called antigens. When a pathogen infects a cell or
is engulfed by an immune cell, its antigens are processed and a major
histocompatibility–antigen complex, in short MHC–antigen complex, is formed and
transported to the cells surface.
Antigens can be recognized by
receptors on the cell surface of different immune cells and cause an immune
reaction. It is generally considered that B
cells bind to antigens on the surface of a pathogen, cytotoxic T cells bind antigens
which are presented by the MHC–antigen complex of an infected or abnormal body
cell. And T helper cells bind to antigens
which are presented by the MHC–antigen complex on antigen presenting cells.
However, other ways of immune cells
binding to antigens can not be excluded. When a T helper cell with T cell
receptor, or in short TCR, that is complementary to a specific antigen approaches an
antigen presenting cell, its CD4 cell surface protein helps the T helper cell to
bind its TCR with the complementary MHC–antigen complex. This binding activates the T helper
cell, which will proliferate and release cytokines.
Cytotoxic T cells and B cells
usually need to bind to an antigen and come into contact with cytokines to be fully
activated. Once activated, the cytotoxic T
cell will proliferate and carry out the cell-mediated immune response and the B cell
will proliferate, differentiate, and carry out the humoral immune response.
Let’s return to the question, which
asks for the name of the cells that are involved in both cell-mediated and humoral
immune responses. We can now complete the
sentence. T helper cells are involved in both
cell-mediated and humoral, antibody, responses.
