Immunology as a Metaphor for Computational ... - Napier University

Chapter 1. Introduction 2amount of research in this area, it thus seems pertinent to examine the immune systemmetaphor in relation to information processing in more detail, and to ask which arethe features of the natural immune system that really distinguish it from other biologicalmetaphors, and to attempt to categorise the types of problem area in which thisparticular metaphor might provide an advantage over others.1.1 ImmunologyThere are four main causes of death to the human being — injury, infection, degenerativedisease and cancer. Of these, only the former two regularly kill their victims beforethey reach child bearing age, and as such are a potential source of lost genes. The immunesystem is an example of a mechanism which may help to ensure the survival ofthose genes, and has evolved over time in order to protect us from infectious organismsexisting in the environment. Thanks to the immune system, infections in a normalindividual caused by microbes such as viruses, bacteria, fungi and parasites are generallyshort lived and leave little permanent damage. The immune response broadly fallsinto two categories — the innate or non-specific response, and the adaptive or specificresponse. The innate response is provided by a number of non-specific chemicals suchas lysozyme which destroys the outer surface of many bacteria, non-specific chemicaleffectors such as macrophages and simple barrier mechanism such as the skin. On theother hand, the adaptive response is highly specific for particular pathogens (antigens),and furthermore, it improves with each subsequent exposure to the pathogen. It cantherefore can be said to ’remember’ specific pathogens. It is with this adaptive aspectof the immune system that artificial models are generally concerned. The adaptive responseconsists of two major phases — a recognition phase followed by a reaction toeliminate the pathogens, and is achieved via a class of immune cells collectively knownas lymphocytes. Recognition is generally accepted to require the immune system to beable to distinguish between the body’s own cells (self) and foreign pathogens, (nonself),though recently some immunologists have controversially rejected this theoryand proposed that in fact the job of the immune system is only to distinguish dangerousnon-self from self ([Matzinger, 1994a, Matzinger, 1994b]. As far as computer