 In 1970, Unanue was given an appointment in the Department of Pathology at Harvard Medical School, where he quickly rose through the academic ranks to become the Mallinckrodt Professor of Immunopathology in 1974.While at Harvard University, he and his colleagues made observations in the areas of immunoglobulin capping on B cells and host defenses to bacteria such as Listeria monocytogenes.That work culminated in the conclusion that MHC molecules mediate the display of processed peptides to T cells.