What is the correct sequence of events for activation of a B cell by a T-dependent antigen? (1) The B cell binds to a cytokine a
nd then interacts with the TH cell. (2) This causes the B cell to bind the antigen, and then the B cell is activated. (1) Immunoglobulin receptors on the B cell recognize and bind the antigen. (2) An antigen fragment in complex with MHC class 2 is displayed on the B cell's surface. (3) The MHC-antigen complex binds a receptor on a TH cell. (4) The TH cell secretes cytokines that activate the B cell. (1) Identical repeating subunits on the antigen bind to many of the antibodies on the surface of the B cell. (2) This activates the B cell. (1) The T cells bind to an antibody on the B cell. (2) The T cell secretes cytokines. (3) The B cell binds the antigen. (4) The B cell is activated by binding to the antigen.
Antigens that activate B-cells with the help of T-cells are called as T-cells dependent antigens. They are called as such because they are not able to induce a humoral response in organisms that lack T-cells. B-cells response to these antigens take many days, thought antibodies generated are more versatile and have a higher affinity than those generated from T-cell independent activation.
So, the steps for activation of a B cell by a T-dependent antigen are:
(1) Immunoglobulin receptors on the B cell recognize and bind the antigen.
(2) An antigen fragment in complex with MHC class 2 is displayed on the B cell's surface.
(3) The MHC-antigen complex binds a receptor on a TH cell.
(4) The TH cell secretes cytokines that activate the B cell.
