Currently, pharmacological preparations based on endogenous regulatory peptides are being actively studied as the most promising class of drugs that are practically devoid of side effects. This class of drugs includes a synthetic analogue of tuftsin Selank. Selank, on the one hand, has an anxiolytic and nootropic effect, and on the other hand, it has pronounced antiviral properties. During the study of the immunomodulatory effect of Selank, we proved that both the whole peptide and its individual fragments can cause significant changes in the expression of genes of chemokines, cytokines, and their receptors in the mouse spleen 6 and 24 hours after a single injection. We also showed that a change in the mRNA level of most of the considered genes is observed after the introduction of Gly-Pro, previously proposed as a minimal fragment of Selank with antiviral activity pharmacophore.