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Chapter 4
T Cell-Inspired
Algorithms
h is chapter presents change/anomaly detection techniques inspired by the T cell
censoring and maturation process in the biological immune system. First, the
main process of negative selection (NS) that results in self/nonself discrimination
is described. h en, the important features of artifi cial NS are presented. Finally,
diff erent variations of negative selection algorithm (NSA) have been considered.
h ere is a signifi cant amount of work on this topic area; therefore, for better read-
ability, this chapter has been divided into three parts.
4.1 Self/NonselfDiscrimination
An important mechanism of the adaptive immune system is the “self/nonself rec-
ognition” (Coutinho, 1980). h e immune system is able to recognize which cells
are its own (self ) and which are foreign (nonself ); thus, it is able to build its defense
against the attacker instead of self-destructing. As mentioned earlier (Chapter 1),
T cells of enormous diversity are fi rst assembled with a “pseudorandom genetic
rearrangement process” and those that recognize self-cells are eliminated before the
rest are deployed into the immune system to recognize and attack foreign patho-
gens. h erefore, T cells go through a process of selection that ensures that they are
able to recognize nonself peptides presented by major histocompatibility complex
(MHC). h is process has two main phases: positive selection (PS) and NS.
During the PS phase, T cells are tested for recognition of MHC molecules
expressed on the cortical epithelial cells. If a T cell fails to recognize any of the
MHC molecules, it is discarded; otherwise, it is kept.
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