Video Transcript
What is the difference between
cell-mediated and humoral, antibody-mediated, immunity? (A) All the immune cells involved
in humoral immunity are B cells, while those in cell-mediated immunity are all T
cells. (B) Humoral immunity responds to
extracellular pathogens, while cell-mediated immunity responds to intracellular
pathogens. (C) Cell-mediated immunity is
rapid, while humoral immunity is a more delayed but sustained response. (D) Humoral immunity involves a
specific response to an antigen, but cell-mediated immunity does not. Or (E) clonal selection occurs in
humoral immunity but not in cell-mediated immunity.
Cell-mediated and humoral immune
responses are types of specific, or adaptive, immunity. Both of these responses target
specific pathogens. So answer choice (D) is
incorrect.
Cell-mediated responses involve
cytotoxic T cells with specific T cell receptors. And the humoral response involves B
cells with specific B cell receptors. Both of these receptors are
specific for the antigen on the pathogen. Other T or B cells that do not
carry a specific receptor for this antigen won’t bind. The process of selecting a T or B
cell that is specific to an antigen is called clonal selection. Both cell-mediated and humoral
responses use clonal selection, so option (E) is incorrect.
In both responses, T helper cells
that are also specific for this antigen are required to activate these cells. So both cell-mediated and humoral
responses require the use of T-helper cells. Therefore, option (A) is
incorrect.
Once activated, these cells can
finally go on to destroy the pathogen. Because of all these prior steps,
adaptive immunity is more delayed than innate immunity, which is more rapid. Since both cell-mediated and
humoral responses are delayed, answer (C) is incorrect.
The activated cytotoxic T cell can
then go on to kill cells that are infected with the pathogen. So they target intracellular
pathogens. And activated B cells can
differentiate into specialized cells called plasma cells that produce
antibodies. Antibodies target pathogens outside
of cells, or extracellular pathogens, by neutralizing them or leading to their
destruction.
So, the correct answer is (B). Humoral immunity responds to
extracellular pathogens, while cell-mediated immunity responds to intracellular
pathogens.
