When T cells are stimulated by antigens, the cell-mediated reaction is initiated by
the binding of antigen with an antigen receptor on the surface of a sensitized T
lymphocyte. Binding of the T cell receptor may occur directly or may be mediated
by macrophage-bound antigen.
Helper cells (Th) proliferate and function to present antigen to antibody-forming B
cells in such a way to facilitate the interaction between antigen and the B cell. The
cells also aid in cell-mediated immune responses.
Suppressor cells (Ts) are defined as cells capable of aborting an otherwise
anticipated immune response and of terminating an ongoing immune response. It
has been shown that there exists Ts cells which are specific for the cell-mediated
immune response and other Ts cells specific for humoral immune responses.
The mechanism by which Tc cells kill target cells is not well understood. Direct
contact between killer and target cell membranes, via undefined receptors,
apparently leads to membrane changes that cause lysis. These Tc cells are
important in transplantation and tumor immunity.
Another mechanism by which T cells bring about cell-mediated immune reactions
is through proliferation of delayed hypersensitivity T cells (Tdh).
The final event is the generation of memory T cells which function in the
anamnestic response upon subsequent encounter with antigen.
End of Lesson 3