Blood platelets in chronic graft-versus-host disease: association with Th1/Th2 ratio

As found in clinical and laboratory studies, platelets not only play a key role in the processes of coagulation and thrombosis, but are also able to actively participate in other pathophysiological processes, including the development of immune reactions. It has been shown that changes in the immune system leading to systemic lupus erythematosus (SLE) are often accompanied by changes in the number of platelets and their activity in the peripheral blood of SLE patients, which correlate with the severity of the clinical manifestations of the disease. Earlier we have studied the standard experimental model of SLE in detail, based on the induction of chronic graft-versus-host disease (cGVHD) in the semi-allogeneic system DBA/2 → (C57Bl/6 x DBA/2)F1. However, the participation of platelets in this immunopathological process has not been studied. There are no data in the literature on the behavior of platelets in cGVHD or on their relationship with the state of Th1/Th2 balance. It can been expected that the platelet count changes according to the development of cGVHD in the used experimental model by analogy with the development of SLE in humans.In the experiments, we used female mice of the DBA/2 strain and (C57Bl/6 × DBA/2)F1 hybrids. Chronic GVHD in a semi-allogeneic system was induced by injecting DBA/2 mouse splenocytes into B6D2F1 hybrid mice: 60-70 × 106 cells intravenously twice with an interval of 6 days. The studied parameters were evaluated three months after the start of the experiment and the formation of lupus-like glomerulonephritis in animals with Th2-dependent cGVHD variant.A decrease in the number of erythrocytes and hemoglobin, a decrease in hematocrit and a parallel increase in the number of reticulocytes in the blood of mice with cGVHD are in good agreement with our earlier conclusion that these animals have autoimmune hemolytic anemia. It was found that, platelets increase significantly with the development of cGVHD unlike other blood cells. Secondary thrombocytosis is observed in the case of the Th2-dependent variant of сGVHD in this model of SLE, while in the group with the Th1-dependent variant of сGVHD, the average number of platelets in the blood does not differ from the control group.