We report here a simple simulation of the immune system in which we analysed the behaviour of responder cells in the presence of target cells. Variable parameters determined the behaviour of the cells within the simulation, and many simulations using the same parameters ensured that statistical variability was achieved. The model demonstrated that high mobility of the target or responder cells produced a more robust response, and that clearance by the immune system was favoured when effector cells moved rapidly compared with the target cells. Therefore, the high motility coefficients exhibited by T cells studied in vivo may play a role in optimizing the effector response to pathogens. Surprisingly, when the number density of responding cells was increased, target cell numbers were limited more effectively, but there was an increased likelihood of a prolonged response.