The Effects And Partial Mechanism Of Prednisone Inhibiting Plasma Cell Differentiation In MRL/MpSlac-lpr Mice

ObjectiveSystemic lupus erythematosus is characterized by large numbers of abnormal activationand proliferation of B cells and plasma cells, leading to the accumulation ofauto-antibodies. Glucocorticoid, as a classical and a basic therapeutic drug forautoimmune disease, has been applied for decades for its strong anti-inflammatory andimmunosuppressive effect. But whether it can regulate the differentiation of plasma celland the regulatory mechanism is rarely reported. In this study, MRL/MpSlac-lpr micewere used to explore the effects and mechanism of prednisone on the process of plasmacell differentiation.MethodsMRL/lpr mice were randomly divided into3groups, which include model group (n=10)and prednisone (2.5,5.0mg/kg) group (n=8). BALB/c mice were set as normal group.Prednisone was dissolved in normal saline (NC) and given intragastrically everyday for13weeks. In the meantime, the normal group and model group mice were treated withan equal volume of NC.The effects of prednisone on MRL/MpSlac-lpr (MRL/lpr) mouse were assessed byevaluating proteinuria levels, survival times, and indices of spleen and thymus. Serumlevels of anti-dsDNA antibody, anti-nuclear antibody and interleukin-21were also detected by enzyme linked immunosorbent assay. The subsets of splenic plasma cellswere quantified by flow cytometry. Splenic mRNA expression of B-lymphocyte inducedmaturation protein-1(Blimp-1) and B-cell lymphoma-6(Bcl-6) were detected byquantitative polymerase chain reaction. Blimp-1and Bcl-6protein of the spleen andkidney were analysed by western blot.Results1. Effects of prednisone on the survival rate in MRL/lpr miceThe model mice developed increased interstitial nephritis with the age. The first mousedied at the age of14thweek in model group while the one in prednisone (2.5mg/kg)treatment group occurred at the9thweek after treatment (the age of17thweek). At theage of21thweek, the survival rate dropped to50.0%in the model group. However, thetreatment groups (prednisone2.5,5.0mg/kg) were75.0%,87.5%, respectively. Therewas no significant difference between the groups.2. Effects of prednisone on the proteinuria in MRL/lpr miceThe level of proteinuria in MRL/lpr mice was higher than that in normal mice(BALB/c). During the treatment of10weeks till13weeks, the mean proteinuria scoresof prednisone (5.0mg/kg) group were significantly and consistently lower compared tothose in model mice.3. Effects of prednisone on indices of spleen and thymus in MRL/lpr miceThe indices of spleen and thymus in MRL/lpr mice rose strikingly compared withnormal ones. And after treatment with prednisone (5.0mg/kg), the two indices droppedobviously4. Effects of prednisone on serum anti-dsDNA antibody, ANA and IL-21inMRL/lpr miceMRL/lpr mice had a significantly higher level of auto-antibodies, including anti-dsDNAantibody and ANA than that in BALB/c mice. Treatment with prednisone (2.5mg/kg, 5.0mg/kg) could result in an obvious decrease in serum ANAs, but had little effect onanti-dsDNA antibodies. Most of all, prednisone could decrease the high-level IL-21inMRL/lpr mice.5. Effects of prednisone on the splenic plasma cells in MRL/lpr miceThe expression of CD19in the spleen lymphocytes of MRL/lpr mice was significantlyreduced compared to the normal group (mean5.67%vs44.10%). The percentages ofplasma cell precursors (CD19+CD27+CD38+) and plasma cells (CD19-CD138+) inmodel group were higher than that in the normal one.The prednisone treatment (2.5mg/kg and5.0mg/kg) could increase the expression of CD19on B cells. It could alsodecrease the high percentages of plasma cell precursors and plasma cells significantly6. Effects of prednisone on the expression of CD138in the spleen of MRL/lprmice.Compared with the normal mice, model mice have a higher expression of CD138. Afterprednisone treatment, the positive cells are decreased significantly.7. Effects of prednisone on the splenic Blimp-1and Bcl-6mRNA expression inMRL/lpr miceThe splenic Blimp-1mRNA and Bcl-6mRNA expressions in MRL/lpr mice were bothsignificantly increased compared to the normal Balb/c mice. After treatment withprednisone, the Blimp-1and Bcl-6mRNA decreased significantly8. Effects of prednisone on the Blimp-1and Bcl-6expression in the spleen andkidney of MRL/lpr miceBlimp-1protein in the spleen and kidney was expressed positively and more remarkablycompared to those of control mice. After treatment, the protein expression in the spleenwas reduced significantly. However, prednisone treatment could not reduce the Blimp-1protein significantly in the kidneyThe expression of Bcl-6was significantly increased in the spleen of MRL/lpr mice. Prednisone could reduce the expression significantly in the spleen. However, there areno significant changes in the Bcl-6expression in the kidneyConclusions1. Prednisone treatment could relieve symptom of SLE in MRL/lpr mice includingreducing the proteinuria level, antibody level, spleen index and thymus index.2. The therapeutic effect maybe associated with the inhibition on IL-21production,down-regulation of Blimp-1and Bcl-6expression, restriction of plasma celldifferentiation.