Objective: To explore the possible role of CD28/CTLA-4 co-stimulators in immune pathophysiology of acquired aplastic anemia(AA).
Methods: By FACS, the percentages of CD28, CTLA-4 expressing CD3+ CD4+ T cells and the level of Th1, Th2 in bone marrow were detected in 23 AA patients at active phase, 10 at recovery phase and 15 normal controls. The relationship between the co-stimulators, Th1, Th2, and absolute neutrophil counts (ANC) was evaluated.
Results: (1) The percentage of CD28 and CTLA-4 expressing CD3+ CD4+ T cells in bone marrow, and CD28+/CTLA-4+ ratios were (31.40 +/- 10.83)%, (2.45 +/- 1.30)% , and 17.02 +/- 13.44 in normal controls respectively, (39.84 +/- 10.89)%, (1.43 +/- 0.67)%, and 43.04 +/- 37.61 in AA at active phase, respectively, (22 +/- 9.08)%, (3.46 +/- 2.26)%, and 10.49 +/- 7.8 in AA at recovery phase, respectively. The percentage of CD28 and CD28+/CTLA-4+ ratio were significantly higher, while CTLA-4 were lower in active phase AA patients than in normal controls (P < 0.05). These values in recovery phase AA were comparable to those in normal controls. (The Th1, Th2, and Th1/Th2 in bone marrow were (4.21 +/- 2.11)%, (1.99 +/- 1.27)%, and 2.46 +/- 1.28 in normal controls respectively, (11.13 +/- 4. 96)%, (2.46 +/- 1.65)%, and 5.20 +/- 1.98 in active phase AA and (5.39 +/- 4.2)9%, (2.53 +/- 2.41)%, and 2.87 +/- 1.43 in recovery phase AA, respectively. The percentage of Th1 and Th1/Th2 ratio were significantly higher in AA patients at active phase than in normal controls (P < 0.05). (3) The CD28+/CTLA-4+ ratio was positively related to the Th1+ /Th2+ ratio (P < 0.05). ANC was negatively related to CD3+ CD4+ CD28+ T cells (P < 0.01), and positively to CD3 + CD4 ' CTLA-4' T cells (P < 0.01) respectively.
Conclusion: (1) The expression of CD28 was increased while CTLA-4 decreased on the membranes of CD3+ CD4+ T cells in bone marrow of AA patients. (2) The abnormal expression of CD28 costimulator promoted the shift of immune balance to Thl type. (3) The unbalance of CD28+ / CTLA-4+ is important for the immune pathophysiology of AA.