Immunotherapy for Infectious Diseases

Humoral Immunity 13
Fig. 7. VDJ joining occurs through DNA recombination.
ANTIGEN-PRESENTING CELLS AND T-CELLS
MHC and Antigen Presentation
Class II major histocompatibility complex (MHC) is an antibody-like protein representing
an extension of the principles by which antibodies are made: MHCs in different
clones have different specificities (like antibodies) but otherwise different structures
and functions. MHCs have � and � chains with binding sites (rather than small and
large chains) and a constant region that anchors the molecule to the plasma membrane
(with a binding site outside the cell) (Fig. 8).
Cytokines
This is a generic term for messenger molecules (polypeptides) secreted by lymphoid
and nonlymphoid cells that form a mediator network regulating the growth, differentiation,
and function of cells involved in immunity, hematopoiesis, and inflammation.
Cytokines secreted by lymphocytes are also called lymphokines, and those secreted by
monocytes/macrophages are known as monokines. An interleukin (IL) is a cytokine
that carries a message between leukocytes. Cytokines involved in the regulation of
T-cells, B-cells, and macrophages were mentioned previously and are summarized in
Table 3. CD 4� helper T-cells are now divided into two subsets based on cytokine profile
and predominant function: