Immunophenotype and TCR-Vβ repertoire of peripheral blood T-cells in acute infectious mononucleosis

Although a number of studies on the phenotypic changes that occur after T-cell activation have already been published, the specific immunophenotypic features of T-lymphocytes and the frequency at which TCR-variable region (TCR-V) restricted T-cell expansions occur “in vivo” during acute viral infection still remains to be established. We report on the immunophenotype and TCR-V repertoire of peripheral blood T-cells from 28 patients with acute infectious mononucleosis. Immunophenotypic studies were performed by flow cytometry using direct immunofluorescence techniques and stain-and-then-lyse sample preparation protocols with three- and four-colour combinations of monoclonal antibodies directed against a large panel of T- and NK-cell associated markers, activation- and adhesion-related molecules and TCR-Vβ, -Vγ and -Vδ families. Nearly all patients (27/28) showed a massive expansion of CD8+/TCRαβ+ T cells, the majority (>90%) of which displayed an immunophenotype compatible with T-cell activation: CD2+high, CD7+low, CD11a+high, CD38+high, HLA-DR+high, CD28+/−low, CD45RO+high, CD45RA−/+low, CD11b−/+low, CD11c+/−low, CD16−, CD56−, CD57−, CD62L−, CD94−, CD158a−, CD161−, NKB1−. Additionally, the levels of both CD3 and CD5 were slightly decreased compared to those found in normal individuals. Late-activation antigens, such as CD57, were found in small proportions of CD8+/TCRαβ+ T-cells. Increased numbers of CD4+/TCRαβ+ T-cells, TCRγδ+ T-cells and NK-cells were also noticed in 17, 16 and 13 of the 28 cases studied, respectively. Evidence for activation of CD4+/TCRαβ+ and TCRγδ+ T-cells relied on changes similar to those described for CD8+/TCRαβ+ although less pronounced, except for higher levels of both CD5 and CD28 in the absence of reactivity for CD11c on CD4+/TCRαβ+ T-cells and higher levels of CD161 and CD94 on TCRγδ+ T-cells. Small expansions of one or more TCR-Vβ families accounting for 12 ± 7% of either the CD8+/TCRαβ+ or the CD4+/TCRαβ+ T-cell compartment were found in 12 of 14 patients studied, whereas the distribution of the TCR-Vγ and -Vδ repertoires tested in 2 of the individuals with expanded TCRγδ+ T-cells was similar to that observed in control individuals. The results presented here provide evidence for an extensive T-cell activation during acute viral infection and establish the immunophenotype patterns associated with this condition.