The repertoire of lymphocyte receptors in the adaptive immune system protects organisms from a diverse set of pathogens. Cells of the immune system have to cover the space of all possible pathogens, but at the same time they cannot trigger an immune response when stimulated with the organisms self proteins. Can we identify signatures of this discrimination task in the cells? The immune system is also dynamic, constantly changing in response to stimulation. What is the optimal update to best anticipate the next viral strain?