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

Chapter 3. Immune Systems for Scheduling 90threshold value M T . (A similar phenomenon is observed in natural systems in whichan antibody does not bind to an antigen until the strength of the bond between the two— the antibody affinity — reaches a certain value). In this case, the match-thresholdis more specifically defined as the number of non wild-card places in which an antigenand antibody match.3.13.1 How many antigens are matched by at least one antibody ?The aim of these experiments is to investigate the amount of overlap occurring in theantibody population, and also to determine whether or not all antigens are at leastpartially recognised. Table 3.4 shows the average number of antigens (from a universecontaining 10 antigens) that were not matched by any antibody, for match-thresholdsM T ranging from 2 to 5. Experiments are performed over a range of values for σ andτ, the size of the antibody and antigen samples respectively.For certain combinations of values of m¤ σ¤ τ¥ , it can be seen that no antibodiesmatch some of the antigens. This is particularly noticeable as the size of τ increases.£This is explained with reference to the fitness function used; for high values of τ,antibodies that successfully match more than one antigen are rewarded most highly.However, in many antigen-universes, it may be impossible to detect common patternsbetween certain subsets of antigen, and hence the completely generalist antibody maynot exist. Examining the actual antigen universe for machine 1 indicates that for somesubsets of antigen, common schemas do exist. Similarly, low values of σ also encouragegeneralist antibodies to evolve, so we may expect poor performance if the value ofσ is too low for certain antigen universes.3.13.2 How many unique antibodies are evolved ?Recalling that the aim of SCHED2 IS is to acquire a collection of antibodies, eachof which represents some commonly occurring pattern in the antigen-universe, thenthe more unique patterns we are able to detect, the more useful the antibodies will beas building blocks for constructing new schedules. Therefore, the final population ofantibodies is examined to determine the exact number of unique antibodies that match