The humoral response is the part of the specific immune response that involves B cells and the antibodies they produce. 'Humoral' refers to body fluids: antibodies circulate in blood plasma, lymph and tissue fluid, so this response works against pathogens and toxins outside cells.The response happens in a sequence:
1. Antigen presentation: a macrophage engulfs a pathogen by phagocytosis and displays its antigens on MHC proteins, becoming an antigen-presenting cell (APC).
2. T helper cell activation: a T helper cell with a complementary receptor binds to the presented antigen. It is activated and divides to form a clone of T helper cells.
3. B cell sensitisation: a B cell with complementary antibody receptors binds the same antigen, takes it in by endocytosis and presents it on its own MHC proteins.
4. B cell activation: an activated T helper cell binds to the antigen presented by the B cell and releases cytokines, which activate the B cell.
5. Clonal expansion: the activated B cell divides by mitosis to form a clone.
6. Differentiation: the clone produces plasma cells, which secrete antibodies (the effector stage), and B memory cells.The first time an antigen is met, this takes several days, because only a few B cells and T helper cells match the antigen and time is needed to activate them and produce enough plasma cells. During this delay the pathogen multiplies and the person develops symptoms.
The humoral response is closely linked to the cell-mediated response, because the same T helper cells activate both B cells and T killer cells.
1. Antigen presentation: a macrophage engulfs a pathogen by phagocytosis and displays its antigens on MHC proteins, becoming an antigen-presenting cell (APC).
2. T helper cell activation: a T helper cell with a complementary receptor binds to the presented antigen. It is activated and divides to form a clone of T helper cells.
3. B cell sensitisation: a B cell with complementary antibody receptors binds the same antigen, takes it in by endocytosis and presents it on its own MHC proteins.
4. B cell activation: an activated T helper cell binds to the antigen presented by the B cell and releases cytokines, which activate the B cell.
5. Clonal expansion: the activated B cell divides by mitosis to form a clone.
6. Differentiation: the clone produces plasma cells, which secrete antibodies (the effector stage), and B memory cells.The first time an antigen is met, this takes several days, because only a few B cells and T helper cells match the antigen and time is needed to activate them and produce enough plasma cells. During this delay the pathogen multiplies and the person develops symptoms.
The humoral response is closely linked to the cell-mediated response, because the same T helper cells activate both B cells and T killer cells.