Studies of lymphocytotoxins in infectious mononucleosis: reduced lymphocyte killing in the acute phase.

Fifty sera from twenty-five patients with uncomplicated infectious mononucleosis (IM) were tested for lymphocytotoxic activity (LCA) against pools of lymphocytes collected from (a) normal donors (b) ten patients during the acute phase of IM and (c) four of these patients during the convalescent phase. The LCA of twenty-four sera from patients with systemic lupus erythematosus (SLE) was also tested against the same panels of cells. The percentage of acute phase lymphocytes killed by sera from patients with IM or SLE was significantly less (P less than 0.001 and P less than 0.05 respectively) than the percentage of normal or convalescent cells killed by the same sera. This reduction could not be explained by lymphocyte donor variation as the same donors were used in the acute and convalescent phases of IM. It is suggested that changes in the surface characteristics of acute IM lymphocytes cause a temporary failure of interaction with circulating lymphocytotoxins. Such a phenomenon could have important influences on the self-limiting nature of the disease.