Role of MP-4 myelopeptide in regulation of antibody production and functional activity of macrophages under stress conditions

Myelopeptides are endogenous low-molecular weight peptides with immunoregulatory activity. Each of these myelopeptides has an individual sequence and plays a role in correction of immune system disorders. In our earlier studies, we have shown immunomodulatory effect of MP-3, MP-5, MP-6 myelopeptides upon functioning of peritoneal macrophages under the conditions of immobilization and cold stresses. The aim of this work was to investigate the effect of MP-4 myelopeptide upon antibody formation, production of reactive oxygen species, and absorptive activity of peritoneal macrophages in mice under the immobilization stress. Materials and methods. The in vivo experiments were carried out in 24 male Swiss mice weighing 17-22 g. Two-or six-hour immobilization stress was produced in the animals. MP-4 was injected intraperitoneally 30 min before the onset of stress, at a dose of 40 μg/kg. The animals were divided into 4 groups: 1, control; 2, stress; 3, stress + MP-4; 4, MP-4 injection. On day +5, cellularity and the number of antibody-forming cells (AOC) in spleen were assessed by the method of local hemolysis in an agarose gel according to Jerne. Production of reactive oxygen species by peritoneal cells was assessed using the luminol-dependent chemiluminescence (LZHL) reaction. The absorption capacity of peritoneal macrophages was assessed using a standard method using a BDFACSCalibur laser flow cytometer. Labeled St. aureus at a final concentration of 10⁸ cells/ml were used as phagocytosis targets. Statistical analysis was performed using the unpaired Student's t-test. Results. It was found that two-hour immobilization stress did not affect the absorption activity of peritoneal leukocytes, whereas six-hour stress suppressed phagocytosis. Injection of MP-4 in stress-exposed animals did not lead to changes in phagocytic activity of peritoneal macrophages. MP-4 did not correct the stress-induced decrease in the number of antibody-forming cells from the spleen during six hours of immobilization, nor stress-induced increase in absolute amounts of AOC under the two-hour immobilization stress. In the group of animals receiving MP-4 and immobilized for two-hours, an increase in the number of nucleated cells was increased, as compared with the control group. Thus, in contrast to the previously studied myelopeptides, MP-4 did not show pronounced immunomodulatory effects upon these parameters.