Main findings
The vast majority of women treated with Anti-D had unremarkable pregnancy and delivery. More than 70% of all pregnant women delivered healthy children. Interestingly, the efficacy of this treatment does not appear to be dependent on age, thrombophilia, and prior treatment. Nevertheless, by these data there could be a relation between those parameters and outcome of a pregnancy, but case numbers are too low for significant statistical analysis. Treatment with Anti-D was safe with no signs of significant hemolysis.
Worldwide, RPL represents a serious and unresolved problem.1,2,6 Immune pathways play a key role in the pathophysiology of RPL. Already at early stage, gestation induces a major immune response which presumably involves all immune cells, including lymphocytes, macrophages and decidual dendritic cells. Thus, the question whether immunotherapy may help in management of RPL is increasingly focused in new studies.18
Macrophages are presumably the main player in regulation of pregnancy, including implantation, placentation, fetal development, parturition, and most importantly vascular remodeling at the maternal-fetal interface. Thus, some modulation of macrophages may prevent miscarriages related to immune imbalance. On this, the question rised, whether a subtle attraction of these cells by coating of autologous red blood cells in such affected women may result in successful pregnancies. In fact, the results obtained during observation were encouraging. The vast majority of treated women had unremarkable pregnancy and delivery. Interestingly, the efficacy of this treatment does not appear to be dependent on age, thrombophilia, and prior treatment. Nevertheless, by these data there could be a relation between those parameters and outcome of a pregnancy, but case numbers are too low for significant statistical analysis. Since all treated women received simultaneously LMWH and/or aspirin, the question remains open whether the beneficial effect was solely related to Anti-D or to a combined effect of both drugs. This is supported by the finding that LWMH beyond its anti-coagulating effect may induce immunomodulation.19Until now, a monotherapy with Anti-D has not been undertaken. However, it has been shown that treatment with intravenous immunoglobulins (IvIg) that somewhat resembles Anti-D, may improve the outcome in pregnant women with miscarriages.
Similarly, there is evidence that polyclonal Anti-D has an immunomodulatory effect, which could not fully be explained yet.20,21 In our experience, this treatment is safe when it is given subcutaneously or at least slowly by intravenous route.22 In previous studies we have demonstrated that the administration of LMWH and/or aspirin results in live births in most women with RPL.7 In this retrospective study, we used low Anti-D doses (2 to 3 times 300 µg) for treatment of RPL in Rh(D) positive women who remained abortive despite treatment with LMWH and/or aspirin.
At first glance, the question may arise whether this treatment could be justified in Rhesus positive pregnant women. Based on the following facts, this treatment is, we think, rational as long as no alternative therapy is available for such affected patients. Anti-D is used in treatment of adults and children since four decades with little or no side effects, if the drug was carefully injected.22The injection of 300 µg is harmless compared to that dose given in ITP (50 - 75 µg/kg body weight), and to that amount reaching Rh(D) positive infants in Rh(D) negative pregnant women who receive at least two times 100 - 300 µg prophylaxis.
The positive influence of Anti-D on RPL is evident as reflected by the significantly increased rates of successful pregnancies in the majority of treated women in our practice. This effect does not appear to be dependent on age, inherited haemophilias or blood group. The question whether Anti-D per se or only in combination with LMWH is effective is a matter of speculation. Since the mechanisms by which LMWH influences the outcome in RPL is largely unknown, a synergic effect can not be excluded. Ultimately, LMWH has been shown to induce in vitro andin vivo a proinflammatory profile on RPL. It has been suggested that this effect could be valuable at the implantation stage.7 Thus, it remains unclear whether Anti-D alone could also be effective as well as the combination with LMWH.
The question why this treatment was ineffective in 26 % of the treated pregnant women remains to be answered. A possible explanation could be related to unknown predisposition factors that cannot be influenced by immunological modulations. Similarly, the phenomenon that the treatment may again result in miscarriage in some women who had been shown to be responsive remains also obscure. Whether this ineffectivity could be related to the giving dose or timing of Anti D admininistration remains to be answered.
Though, the most possible explanation for the successful pregnancy following treatment with Anti-D may be attributed to an immunomodulatory effect, some other questions remain open. For example, when and by which mechanisms Anti-D may induce the tolerance of the semiallogeneic fetus. There is no doubt that pregnancy is surroundingly controlled by immune reactions which simultaneously maintain immune response (defense) and tolerance (semi-allogeneicity), respectively. 10,11,23
Changes during pregnancy include an increase in phagocytic cells and their functional capacity to ingest IgG coated RBCs,24an increase of T and B regulatory cells, reduction of natural killer cells, and polarization of decidual macrophages.23,25-28 It has been demonstrated that RPL is associated with an imbalance of pregnancy related immune haemostasis,10,11,29 which could, at least in part, be normalized by immunomodulation.18,30
Anti-D administration into Rh(D) positive pregnant women results in coating of autologous RBCs with IgG antibodies. This happening represents a dangerous signal, and attracts macrophages to recognize IgG opsonized RBCs. Although the attracted macrophages do not appear to ingest a significant amount of the IgG coated RBCs, they could be influenced in the presence of IgG-coated RBCs.
In addition, polyclonal Anti-D may contain antibodies other than Anti-D which may have influence on macrophages, independent of phagocytosis, i.e. HLA and anti-idiotype antibodies. Thus, it would not be surprising that the reactions to Anti-D may lead to polarization of decidual macrophages. These cells exhibit wide plasticity and are sensitive to small microenvironmental changes, including nutrition, smoking, toxins, inflammation, and physiological stress.13-15
It seems that the M1 subtype predominates over the M2 subtype in RPL. Coating of autologous RBCs with antibodies represents unphysiological condition in vivo , which may lead to polarization of M1 to M2 phenotype. The latter cells seem to be responsible for immunotolerance, which is a prequisite for successful implantation a fetal development.
This hypothesis can only be proved by phenotyping of decidual macrophages prior to and following treatment. Alternatively, an extended investigation of cytokines and changes of peripheral immune cells may give an explanation of this phenomenon.8-11,26,28