Objective: To evaluate the impact of luteinizing hormone-releasing hormone (LHRH) on the protection of thymic function after allogenic hematopoietic stem cell transplantation (allo-HSCT).
Methods: Murine model of MHC mismatched allogeneic HSCT (C57BL/6-->BALB/c) was established. The severity of acute graft-versus-host-disease (GVHD) was assessed according to a clinical scoring system. The intra-cellular levels of IFN gamma, TNFalpha and IL-1 beta in thymocyte were analyzed by protein array and thymic function by quantification of signal-joint TCR rearrangement excision circles (sjTRECs).
Results: All recipients in group A (allogeneic mice), B (allogeneic LHRH castrated-mice) and C (syngenic mice) achieved hematopoietic reconstitution. White blood cell (WBC) over 1.0 x 10(9)/L in groups A, B and C were on day (11.2 +/- 1.4), day (9.8 +/- 0.6) and day (9.7 +/- 0.7), respectively (P = 0.003, 0.002). The onset of acute GVHD in group B was (14.1 +/- 0.7) d and in group A was (11.4 +/- 1.2) d (P = 0.000). All mice in groups A and B developed acute GVHD. No mice occurred aGVHD in group C. The average scores of acute GVHD in groups A and B were (9.1 +/- 0.7) and (5.1 +/- 1.0), respectively (P = 0.000). The levels of IFN gamma, TNFalpha and IL-1 beta in control group were (2.3 +/- 2.5) ng/ml, (1.7 +/- 1.1) pg/ml and (1.8 +/- 1.2) pg/ml, respectively. The IFN gamma levels in groups A, B and C were (10.5 +/- 2.1) ng/ml, (6.7 +/- 2.1) ng/ml and (5.2 +/- 3.3) ng/ml, TNFalpha levels were (7.0 +/- 2.6) pg/ml, (4.3 +/- 0.8) pg/ml and (3.0 +/- 1.8) pg/ml, and IL-1 beta levels were (24.9 +/- 9.0) pg/ml, (17.4 +/- 3.9) pg/ml and (10.8 +/- 3.1) pg/ml, respectively. There were significant differences in the levels of cytokines between group A and the control group (P = 0.000, 0.000, 0.000). The levels of cytokines in group B were significantly higher than those in control group (P = 0.000, 0.003, 0.000). The levels of IFN gamma and IL-beta in group C were significantly higher than those of in control group (P = 0.015, 0.013), and so did in group A than in group B (P = 0.002, 0.002, 0.004), and in group A than in group C (P = 0.000, 0.000, 0.000). The analysis of linear regression showed that the average levels of IFN gamma and TNFalpha paralleled with aGVHD scores (r(2) = 0.359, P = 0.045; r(2) = 0.228, P = 0.019). The average sjTRECs copies/1000 PBMNCs were (39.4 +/- 44.7) in the control group and (12.3 +/- 13.0), (58.0 +/- 71.8) and (19.6 +/- 14.6) in groups A, B and C, respectively. There was no significant difference in the multiple comparisons of peripheral blood levels of sjTRECs among these four groups (P = 0.468).
Conclusion: IFN gamma, TNFalpha and IL-1 beta might be involved in the damage to the thymus by acute GVHD. Sex steroid inhibitor can not only reduce the severity of thymic damage after allo-HSCT, but also reduce the severity of aGVHD and the mechanism might be associated with the reduction of intra-cellular levels of IFN gamma in thymocyte.