Antigen recognition and evolution in a bit-string population model

We present a simple model of selection and mutation of cell populations in the immune system. This is based on generic assumptions and in this respect it resembles a model for evolution in simple ecosystems. In this case the selection acts by means of the affinity function representing the ability of a certain class of lymphocytes to recognize a foreign antigen. Carrying out some analytical and numerical studies we determine the critical values for the parameters ruling the selection and mutation.