Immunology Basics - Immunological Computation: Theory and Applications - page 6

Antigen

Antigen-binding
site

Antigen-binding
site

Epitope
(antigenic
determinant)

SS

SS

c c

CC

(a) (b)

Figure 1.4 Details of an antibody molecule—surface Ig contains four polypep-
tide chains: two identical light chains and two identical heavy chains. Each chain
comprises a variable region ( V ) and a constant region ( C ). Both V regions
combine to form two antigen-binding sites. (a) Antibody molecule, (b) enlarged
antigen-binding site.

Cytokines are mainly secreted by lymphocytes; however, they can also be pro-
duced by other immune and nonimmune cells, for example, those cells that secrete
cytokines when they get damaged (Abbas and Lichtman, 2004; Baumann and
Gauldie, 1994). Cytokines secreted by lymphocytes are called lymphokines and they
have a strong infl uence over immune processes. Lymphokines produced by a lym-
phocyte to communicate with other lymphocytes are called interleukins.

1.1.2.4 Peptides, Major Histocompatibility Complex,

and Antigen Presenting Cells

h e term peptide refers to a short chain of amino acids, usually obtained by the
fragmentation of an antigen, and presented to other cells of the immune system by
antigen presenting cells (APC).
Antigen presentation refers to processing a suspicious foreign particle. Such a
particle is broken up into peptides, and then such peptides are held on the surface
of APC, where T cells can recognize them. Several types of cells may serve as APC,
including macrophages, dendritic cells, and B cells. For instance, macrophages act
as phagocytes which engulf foreign antigens, and then antigens become interna-
lized, processed, and expressed on the macrophages' surface.
In contrast, major histocompatibility complex (MHC) proteins act as “sign posts”
that display peptides on the surface of a host cell. All MHC molecules receive