Previous studies have shown that Huosui Formula has a synergistic effect on the immune and hematopoietic regulation of patients with myelodysplastic syndrome, but the specific mechanism is not yet clear.

To explore the effect and mechanism of Huosui Formula on bone marrow hematopoiesis in rats with myelodysplastic syndrome.

A total of 70 SD rats were randomly divided into a normal control group (n=10), a model group (n=15), a western medicine group (n=15), a low-dose Huosui Formula group (n=15), and a high-dose Huosui Formula group (n=15). Except for the normal control group, the other four groups were injected with dimethylbenzanthracene via the tail vein to induce the establishment of rat myelodysplastic syndrome models. After modeling, the normal control group and the model group were given normal saline; the western medicine group was given thalidomide capsules 10 mg/kg and retinoic acid tablets 4 mg/kg, and the low-dose Huosui Formula group and the high-dose Huosui Formula group were given 1.5 and 6 g/kg Huosui Formula, respectively, by intragastric administration once a day for 28 consecutive days. Peripheral blood and femoral bone marrow tissue were collected to detect peripheral blood routine and bone marrow biopsy hematopoietic proliferation. Flow cytometry was used to detect T lymphocyte subsets and the expression of CTLA-4 and PD-1 on T lymphocytes.

(1) Compared with the normal control group, peripheral blood leukocyte, neutrophil, hemoglobin, platelet, and CD4⁺, CD4⁺/CD8⁺ levels were decreased in the model group significantly (P < 0.05), while CD4⁺PD-1⁺, CD8⁺PD-1⁺, CD4⁺CTLA-4⁺, and CD8⁺CTLA-4⁺ expressions were significantly upregulated (P < 0.05). (2) In all dosage groups, myelopoietic proliferation was increased compared with the model group, with no significant difference between the groups (P > 0.05). (3) Compared with the model group, leukocytes, hemoglobin, platelets, and CD4⁺, CD4⁺/CD8⁺ were significantly elevated in the high-dose Huosui Formula group (P < 0.05), the expression of CD8⁺ was significantly lower (P < 0.05), and the levels of CD4⁺PD-1⁺, CD8⁺PD-1⁺, CD4⁺CTLA-4⁺, and CD8⁺CTLA-4⁺ were down-regulated but not statistically significant (P > 0.05). (4) The western medicine group and the high-dose Huosui Formula group showed similar efficacy. The improvement of each index in the high-dose Huosui Formula group was superior to that in the low-dose Huosui Formula group. These findings indicate that Huosui Formula can improve the bone marrow hematopoiesis in myelodysplastic syndrome model rats, increase the levels of CD4⁺, and CD4⁺/CD8⁺ while down-regulate the expression levels of CD4⁺PD-1⁺, CD8⁺PD-1⁺, CD4⁺CTLA-4⁺, and CD8⁺CTLA-4⁺. These observations suggest a link to the negative immunoregulation mechanism.