A Possible Basis for Immunological Tolerance

Abstract

THE following hypothesis is based on the possibility that, although the mechanism for the entrance of macromolecules into the cell may be the relatively non-specific phenomenon of pinocytosis, the mechanisms for secreting materials out of the cell may be specific. These unknown (probably active) transport mechanisms will, for ease in referring to them, be called ‘secretases’, by analogy to the bacterial permeases, which are concerned with entry rather than exit mechanisms¹. Simple diffusion would account for only a small part of the macromolecular traffic in either direction across the membrane, since most of the ‘pores’ or holes in the cell membrane would be too small to allow passage of the large protein molecules.