A large fraction of T lymphocytes respond to allogeneic cells. Products of the major
histocompatibility (H) complex influence the antigenicity of other cell surface components.
We propose that lymphocytes responding to cells that differ genetically only at the major H
locus recognize not only the major H difference, but also a multitude of other surface
components in combination with the major H antigens. The large frequency of lymphocytes
responding to allogeneic cells, then, becomes a function of the number of complex antigens …