Inhibition of IL-1β and TNFα Gene Expression by IVIg or Anti-Red Blood Cell Antibodies in a Mouse Model of ITP.

Plasma-derived human IgG (IVIg) have been used for more than 2 decades for the treatment of several autoimmune diseases such as ITP, even if their mechanism of action is still not fully understood. Recently, several studies with IVIg-treated patients have shown that IVIg can modulate the serum level of both pro-inflammatory and anti-inflammatory cytokines. In ITP, it is known that the destruction of autoantibody-coated platelets occurs mainly in the spleen. We thus used a mouse model of ITP to evaluate the modulatory effects of IVIg on the expression of several cytokine genes in the spleen of the animals by quantitative RT-PCR. The results showed that the induction of platelet destruction following injection of monoclonal anti-platelet antibodies (MWReg30) in BALB/c mice did not change the expression level of IL-1ra and IL-10 (anti-inflammatory cytokines) and IL-6, IFNγ and MCP-1 (pro-inflammatory cytokines). In contrast, MWReg30-treated mice showed an increase in IL-1β and TNFα mRNA expression by up to 4.2 and 2.1 fold respectively compared to control mice. Treatment of thrombocytopenic mice with IVIg (2g/Kg) prevented the increase of IL-1β mRNA but not TNFα mRNA. In parallel, the effect of anti-red blood cell (anti-RBC) antibodies, used to mimic anti-D treatment of ITP patients, was analysed. The results were similar to those observed with IVIg for IL-1β mRNA, but in contrast to IVIg, anti-RBC treatment also prevented the increase in TNFα gene expression, suggesting that the mechanisms of action of IVIg and anti-D in ITP treatment are different, in agreement with previous studies. In summary, we showed that IVIg and anti-RBC treatments attenuate the expression of important pro-inflammatory cytokines. IL-1β and TNFα are known to increase the phagocytic activity of macrophages and also to enhance the production of antibodies by B cells. Therefore, IVIg and anti-D could contribute to the prevention of platelet destruction in ITP by limiting the activation of phagocytes and the production of autoantibodies. This study was assisted by a grant from the Bayer/CBS/HQ partnership Fund to RB and RL.