Objective. To study the T-cellular immunity in patients with infectious mononucleosis (IM) in the acute period and during the recovery.

Materials and methods. Sixty five blood samples taken from patients with infectious mononucleosis treated at the Minsk Municipal Clinical Infectious Hospital in the acute period and during the recovery. The patients were tested immunologically twice: before the hospital admittance (Group P1) and in 2—3 months after their discharge (Group P2). Healthy volunteers’ tests served the control. The cell subpopulation was identified by the flow cytometry.

Results. During the acute period, the CD3+ cells absolute and relative levels were increased, the CD3+CD8 cells levels were elevated significantly. The ratio of the activated T-cells expressing the CD3+HLA-DR molecule was shown to be increased markedly (up to 75% of the lymphocyte total number). The T-regulatory cells absolute and relative amounts were found to reduced reliably, the TCM cells absolute and relative contents were elevated significantly (P£0.05) and the naive T-cells relative number was reduced (P£0.0001). The naive T-cells absolute amount and the TEMRA subpopulation did not differ from the healthy volunteers’ values (P£0,05). The absolute and relative levels of the exhausted T-cells with the CD3+PD-1+ and CD3+Lag-3+ (Р£0.005) phenotypes and the absolute amount of those with the CD3+Tim-3+ (Р=0.03) phenotype were revealed to be elevated in the peripheral blood assays evidencing about the exhausted T-cells role in the IM immune pathogenesis.

Conclusion. The study performed demonstrated a complex of various changes in the T-lymphocyte subpopulations amounts in the IM patients. On the one hand, the reduced number of the regulatory cells leads to the anti-infectious immunity improvement and, on the other hand, it does not allow control the CD3+CD8+ Т-cytotoxic lymphocytes excessive proliferation. The exhausted T-cells amount increase may be a compensatory mechanism making possible the immunity response balancing.