Amelioration of Murine Passive Immune Thrombocytopenia by IVIg and a Therapeutic Monoclonal CD44 Antibody Does Not Require the Myd88 Signaling Pathway

Abstract

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by a low platelet count and the production of anti-platelet antibodies. The majority of ITP patients have antibodies to platelet integrin αIIbβ3 (GPIIbIIIa) which can direct platelet phagocytosis by macrophages. One effective treatment for patients with ITP is intravenous immunoglobulin (IVIg) which rapidly reverses thrombocytopenia. The exact mechanism of IVIg action in human patients is unclear, although in mouse models of passive ITP, IVIg can rapidly increase platelet counts in the absence of adaptive immunity. Another antibody therapeutic that can similarly increase platelet counts independent of adaptive immunity are CD44 antibodies. Toll-like receptors (TLRs) are pattern recognition receptors which play a central role in helping direct the innate immune system. Dendritic cells, which are notable for their expression of TLRs, have been directly implicated in IVIg function as an initiator cell, while CD44 can associate with TLR2 and TLR4. We therefore questioned whether IVIg, or the therapeutic CD44 antibody KM114, mediate their ameliorative effects in a manner dependent upon normal TLR function. Here, we demonstrate that the TLR4 agonist LPS does not inhibit IVIg or KM114 amelioration of antibody-induced thrombocytopenia, and that these therapeutics do not ameliorate LPS-induced thrombocytopenia. IVIg was able to significantly ameliorate murine ITP in C3H/HeJ mice which have defective TLR4. All known murine TLRs except TLR3 utilize the Myd88 adapter protein to drive TLR signaling. Employing Myd88 deficient mice, we found that both IVIg and KM114 ameliorate murine ITP in Myd88 deficient mice to the same extent as normal mice. Thus both IVIg and anti-CD44 antibody can mediate their ameliorative effects in murine passive ITP independent of the Myd88 signaling pathway. These data help shed light on the mechanism of action of IVIg and KM114 in the amelioration of murine ITP.

The Role of CD44 in Disease Pathophysiology and Targeted Treatment

“…The efficacy of anti-CD44 antibodies has been evaluated in murine models of autoimmune and inflammatory diseases including thrombocytopenia and arthritis. Immune thrombocytopenia is an autoimmune bleeding disorder characterized by a low platelet count and the production of anti-platelet antibodies ( 119 , 120 ). While the standard treatment for immune thrombocytopenia is passive infusion of immunoglobulins, several anti-CD44 antibodies have been shown to ameliorate immune thrombocytopenia.…”

Mesenchymal stem cells improve platelet counts in mice with immune thrombocytopenia

“…Some studies have demonstrated the effectiveness of IVIG in increasing the PLT count and the potential mechanism by using the passive model. 25,26 This ITP model can reflect the progression stage of ITP and has been extensively utilized to rapidly evaluate the efficacy of various therapeutic options. 27,28 In our study, we induced an improved passive ITP mouse model by dose-escalation injection of the anti-CD41 antibody MWReg30 daily and found that the PLT counts were significantly increased on the 2nd day and remained at relatively high levels to alleviate bleeding symptoms after MSC administration.…”

“…Meanwhile, the passive model can prevent the rebound of PLTs and monitor the efficacy of therapeutics more sensitively. Some studies have demonstrated the effectiveness of IVIG in increasing the PLT count and the potential mechanism by using the passive model . This ITP model can reflect the progression stage of ITP and has been extensively utilized to rapidly evaluate the efficacy of various therapeutic options .…”

CD44 antibody–mediated amelioration of murine immune thrombocytopenia (ITP): mouse background determines the effect of FcγRIIb genetic disruption

“…Antibodies to CD44 as well as intravenous immune globulin (IVIG) can both be used to treat murine passive immune thrombocytopenia (ITP), an acute model in which a PLT antibody is passively administered to induce thrombocytopenia in an FcγRIIIa‐dependent (Teeling et al . and Crow & Lazarus, unpublished, 2003), complement‐independent manner.…”