Theoretical Models of Immune Processes - Immunological Computation: Theory and Applications - page 29

Restriction of one pattern to one diff erentiated cell and retention of this pat-
tern by clonal descendants

Generation of new random genetic changes subsequently expressed as diverse
antibody patterns by a form of accelerated somatic mutation

Other researchers also investigated the clonal selection to understand how cer-
tain types of B and T lymphocytes are selected for destruction of specifi c antigens
invading our body.

2.2 Immune Network Theory
h e “immune network (IN) theory” was developed by Niels K. Jerne (Jerne, 1974) in
an attempt to explain how the immune memory gets formed. He hypothesized that
the immune system acts as a regulated network of antibodies and anti-antibodies,
called an “idiotypic network,” which recognizes one another (even in the absence
of antigens) rather than being a set of isolated clones (antibodies of the same speci-
fi city) that respond only when stimulated by antigens. According to Jerne, B and
T cells form a complex circuitry of interacting cells that functions either to stimulate
or to suppress the immune activation. Although there is evidence of the existence
of the idiotypic network, its physiological relevance has been much debated. More-
over, the complexity of idiotypic networks has made it di cult to predict whether
administration of anti-idiotype antibodies or T cells bearing anti-idiotype receptors
up- or down-regulate immune responsiveness (Kuby et al., 2000).
Mature B lymphocytes carry highly specifi c receptors (antibodies) on their sur-
face. h ese receptors are stimulated by complementary structures and such stimu-
lation causes proliferation of particular antibodies (Figure 2.2). h e portion on an
antigen's surface that an antibody is able to recognize is called an epitope, and the
corresponding part of an antibody used to recognize antigens is called a paratope;
an antibody's epitope is called an idiotype (see Figure 2.3).
According to Jerne's theory, a sequence of events forms an idiotypic network as fol-
lows. First, an antigen is recognized by B cells, which secrete antibodies Ab1. Ab1 anti-
bodies themselves are also recognized by “anti-idiotypic” B cells that secrete antibodies
Ab2. h us, further interactions can lead to Ab3 antibodies that recognize Ab2 and so
on. In an idiotypic network, there is no intrinsic diff erence between an antigen and
antibody; and any node of the network can bind to and be bound to by any other.
Several IN models have been proposed, which can be classifi ed into three genera-
tions, where each version of IN incorporates additional features of immune processes.

2.2.1 First-Generation Immune Networks

First generation IN (FGIN) model tries to predict the number of diff erent types of
antibodies (clone) present in the blood. h e increase or decrease of the number of