PD-1 AND Tim-3 Expression on different subpopulations of monocytes in chronic often recurrent herpesvirus infection

More than half of the world’s population is infected with the herpes simplex virus. In most cases, infection is not accompanied by symptoms, but in some people the disease occurs as a chronic infection with frequent and severe relapses. One of the most likely reasons for this may be a dysregulation of the immune system. In recent years, the role of checkpoint molecules, in particular PD-1 and Tim-3, in the regulation of the immune response and the functions of immunocompetent cells has been actively studied. Activation of PD-1 and Tim-3 on T cells has previously been shown to suppress the immune response. PD-1 and Tim-3 are also expressed on other immune cells, in particular monocytes. However, the expression of these molecules on monocytes during chronic viral infections has not been previously studied. The study was aimed at assessing the level of PD-1 and Tim-3 expression on various populations of monocytes in patients with chronic often recurrent herpesvirus infection. Twenty-six patients were recruited into the study. All patients received antiviral and immunomodulatory therapy in the immunological department. The number of classical, intermediate, and non-classical monocytes and the expression of PD-1 and Tim-3 on monocytes, were assessed by flow cytometry before and after the therapy. Monocytes were isolated from peripheral blood, and subpopulations were divided according to the level of expression of CD14 and CD16. In patients with herpes, a reduced number of monocytes was observed in comparison with healthy donors. The relative number of PD-1-positive monocytes, the mean fluorescence intensity of PD-1 and Tim-3, and the number of double-positive cells were reduced in herpes patients in all three monocyte subpopulations examined. Three months after therapy, the response to the therapy was assessed; patients who did not have a single recurrence of herpes within 3 months were considered to respond. Responding patients had a lower initial content of double-positive cells among intermediate and non-classical monocytes. The decrease in the level of PD-1 and Tim-3 positive monocytes during herpesvirus infection revealed in the present study may indicate the involvement of monocytes deficient in the expression of checkpoint molecules in the pathogenesis of the disease.