Final answer:
Thymus (T Cell) dependent antigens are molecules that require T cell help to induce B cells to produce an antibody response, often involving protein antigens and the assistance of Th2 cell-secreted cytokines.
Step-by-step explanation:
Thymus (T Cell) dependent antigens are complex molecules, usually proteins, that require the assistance of T cells to induce an antibody response in B cells. When a B cell receptor recognizes a T cell-dependent antigen, it internalizes and processes the antigen, presenting peptides on its surface bound to MHC class II molecules. At this point, Th2 cells, which are a type of helper T cell, interact with the presented antigen.
These Th2 cells then secrete cytokines that are essential for the activation of the B cell into an antibody-secreting plasma cell. In contrast, T cell-independent antigens do not require T cell help for activation of B cells. These antigens often have repeating units, such as carbohydrates on bacterial cell walls, that can crosslink B cell receptors directly, leading to B cell activation without T cell intervention.