Cell communication in tissue P systems: universality results

We introduce an evolution-communication model for tissue P systems where communication rules are inspired by the general mechanism of cell communication based on signals and receptors: a multiset can enter a cell only in the presence of another multiset. Some basic variants of this model are also considered where communication is restricted either to be unidirectional or to use special multisets of objects called receptors. The universality for all these variants of tissue P systems is then proved by using two cells (three cells in the case of unidirectional communication) and rules of a minimal size.