Control mechanisms in infectious mononucleosis.

The blood mononuclear cells from forty-six patients with infectious mononucleosis were separated into populations of normal and atypical cells by velocity sedimentation. Both populations were characterized in terms of surface markers and response to standard mitogens. The atypical cells were of both T- and B-lymphocyte origin. Some reactivity of the normal against the freshly isolated atypical cells was detected by mixed lymphocyte reactions and 51Cr release, but this was less marked than that obtained against autochthonous lymphoblastoid cell lines. Both normal and atypical lymphocytes were stimulated by and were cytotoxic for lymphoblastoid cell-line cells. It is concluded that the atypical cells consist of two populations, a major one which is part of the host reaction to EB virus-infected cells, and a minor one which is the target for immunological responses and may represent cells transformed by virus.