We offer a new logic, a multimodal epistemic ?ukasiewicz logic, which is an extension of the infinitely valued ?ukasiewicz logic, the language of the logic is an extended by unary connectives that are interpreted as modal operators (knowledge operators). We propose the use such a logic in studying immune system. A relational system is developed as a semantic of this logic. The relational systems represent the immune system which in its turn is a part of relational biology.