Serum migration inhibitory activity and monoclonal antibody-defined T-cell phenotypes in patients with acute infectious mononucleosis.

Previous experiments in our laboratory have demonstrated that circulating endogenous leucocyte (migration) inhibitory factor (serum LIF), or a lymphokine with LIF-like activity, may be involved in the impaired cellular immune response observed during the acute phase of the Epstein-Barr virus (EBV) induced infectious mononucleosis (IM). To determine whether serum LIF activity is associated with immunoregulatory IM T-cell subset abnormalities, we analyzed the peripheral blood T-cell populations in a series of acute serum LIF-positive and LIF-negative IM patients by means of T-lymphocyte-specific monoclonal antibodies. Although there was both activation and increase of suppressor/cytotoxic T cells in all IM patients sampled in the acute stage, the relative and absolute numbers of suppressor lymphocytes were found to be significantly higher in those who had LIF activity in their serum. It is postulated that EBV infection can preferentially activate a specific T-cell subpopulation which, in its turn, inhibits the overall host immune response, possibly by a LIF-induced feedback suppression mechanism.