In vitro polyclonal immunoglobulin (Ig) production and immunoregulation were studied in peripheral blood lymphocytes (PBL) from 17 acute (<2 weeks after onset of symptoms) and 14 convalescent (2 to 5 weeks after onset of symptoms) Epstein-Barr virus (EBV)-induced infectious mononucleosis (IM) patients. PBL from both groups developed fewer anti-sheep red blood cell (SRBC) plaque-forming cells (PFC) (p < 0.001) and fewer intracytoplasmic (ICP) Ig-positive cells (p < 0.01) than normal PBL after in vitro stimulation with pokeweed mitogen (PWM). However, there was a significant trend toward increased PWM-induced anti-SRBC PFC with increasing time after onset of IM symptoms (R = 0.389, p < 0.025). PBL from acute but not convalescent IM patients significantly suppressed the PWM-induced anti-SRBC PFC response (15 ± 8% of expected, p < 0.001) and the ICP Ig response (21 ± 8% of expected, p < 0.001) of normal PBL in allogeneic co-cultures. The suppressor cell activity in PBL of acute IM patients was removed by treatment with anti-T cell antiserum and complement as well as by the addition of 10-5 M hydrocortisone to the cell cultures.

In addition, acute IM cells in the presence of normal T cell help were able to respond normally in vitro to PWM to generate both anti-SRBC PFC and ICP Ig. Thus, PBL from both acute and convalescent IM patients manifest decreased Ig production after in vitro polyclonal stimulation. These decreased responses were associated with the emergence of corticosteroid sensitive suppressor T cells that were demonstrable in PBL of acute IM patients, and were no longer demonstrable in PBL of convalescent IM patients. The transient presence of peripheral blood suppressor T cells in these acute IM patients was associated with an uneventful clinical course and may represent in vivo immunoregulatory cell activation in response to EBV-induced polyclonal B cell activation.

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