Soluble forms of p55-IL-2R alpha, CD8, and CD30 molecules as markers of lymphoid cell activation in infectious mononucleosis.

BACKGROUND: Epstein-Barr virus (EBV) infection in infectious mononucleosis (IM) is associated with lymphocyte activation leading to the expansion of cells expressing activation-associated antigens. Most of these antigens are released as soluble molecules in vitro and in vivo. METHODS: We investigated the serum levels of the soluble forms of the CD8 (sCD8), p55-IL-2R alpha (sIL-2R alpha), and CD30 (sCD30) molecules in 55 patients following primary EBV infection. These data were compared with the phenotypic pattern of circulating lymphoid subsets. RESULTS: In all cases at presentation, lymphocytosis, mainly characterized by the expansion of a CD8+, HLA-DR+, p75-IL-2R beta+, p55-IL-2R alpha- population, was associated with high levels of the investigated soluble molecules. Their mean values (+/- SD) were: 17,172 +/- 12,885 U/mL for sCD8 (vs 334 +/- 95 in controls), 2,922 +/- 2,813 U/mL for sIL-2R alpha (vs 331 +/- 115 in controls), and 477 +/- 451 U/mL for sCD30 (vs 4.9 +/- 6.4 in controls). Follow-up study (15 cases, up to 60 days) showed a progressive decline of all soluble molecules, associated with a reduction of activated CD8+/HLA-DR+/p75-IL-2R beta+ T-cells. By the 30th day, values of sIL-2R alpha and sCD30 (729 +/- 333 U/mL and 20 +/- 21 U/mL, respectively) were only slightly higher than in normal controls, whereas sCD8 levels remained consistently higher (1,777 +/- 1,385 U/mL, p < .001). CONCLUSIONS: sCD8, sIL-2Ra and sCD30 serum levels in IM reflect the total bulk and/or the activation-related events of infected and reactive cells. The variations in these soluble molecules during the follow-up provide useful information on the in vivo biological modifications occurring after EBV infection.