Is the MHC a general self-recognition system playing a major unifying role in an organism?

From the review of several recent observations of cell-cell interactions, which occur preferentially in autologous or syngeneic situations such as rosettes, adhesion, homing, and contact inhibition, the existence of an active general process of cellular self-recognition, not limited to the immune system, is postulated. This process is MHC associated or dependent, and seems to require an identity of ubiquitous molecules of class I--or other linked gene products at the surface of interacting cells. In contrast, class II molecules are not apparently implicated in general self-recognition. The immune system is regarded as a late evolution from a self-recognition system. It retains the ability of self-evolution, but possesses the exclusive property of active discrimination against foreignness. The astonishing fact that identity of MHC products seems to be needed for recognition is discussed in the context of various possible mechanisms. From immunological and genetical consideration, it is proposed that the genuine biological role of the MHC would be that of a self-recognition and unifying system.