Discovery of novel autoantibody that is a major risk factor for recurrent pregnancy loss

A research group centered around Kobe University Graduate School of Medicine’s Professor YAMADA Hideto and Associate Professor TANIMURA Kenji (Department of Obstetrics and Gynecology), and Professor ARASE Hisashi et al. of Osaka University’s Research Institute for Microbial Diseases (RIMD) have revealed for the first time in the world the high frequency of a novel autoantibody in women suffering from recurrent pregnancy loss. Joint research by Kobe University and Osaka University in 2015 previously discovered that this autoantibody also causes diseases such as thrombosis.

It is expected that these results will contribute towards the illumination of the underlying mechanisms behind recurrent pregnancy loss, thrombosis and pregnancy complications such as hypertensive disorders; leading to the development of new treatment methods.

The findings were published online on June 25 in the American College of Rheumatology’s journal ‘Arthritis and Rheumatology’.

Main points

  • Those with recurrent pregnancy loss (RPL) experience repeated miscarriages and stillbirths, making them unable to give birth to a healthy baby.
  • In Japan, approximately 1,400,000 women are believed to suffer from RPL. In more than half of cases the cause cannot be determined, making it difficult to prescribe a treatment method. This is a big problem, especially in light of Japan’s low birthrate and aging population.
  • This study was based at Kobe University, which is putting a lot of effort into RPL research, and covered 227 patients in five university hospitals across the country. Approximately a quarter of these patients tested positive for the novel autoantibody (neo-self antibody). Furthermore, almost one fifth tested positive for the neo-self antibody among patients for whom common tests had been unable to determine the cause.
  • It is expected that these results can illuminate the underlying mechanisms behind RPL, thrombosis and hypertensive disorders of pregnancy, leading to the development of new treatment methods. Furthermore, it is hoped that these research results can be the key to solving the low birthrate and aging population issues.

Research Background

Recurrent pregnancy loss (RPL) is a disorder in which the sufferer is able to get pregnant yet experiences repeated miscarriages and stillbirths, making them unable to give birth to a healthy baby. There is believed to be an estimated 1,400,000 women with RPL in Japan. Given Japan’s low birthrate and aging population, this is an important issue to overcome. However, at present the cause remains unknown in over half of patients, making it difficult to know how to cure RPL in many cases.

However, joint research conducted by RIMD’s Professor Arase Hisashi and Kobe University’s Associate Professor Tanimura Kenji discovered a completely new autoantibody that causes antiphospholipid syndrome. This syndrome can lead to the occurrence of thrombosis (in which blood clots can block up blood vessels in vital organs, endangering life such as by causing a stroke), miscarriages, and hypertensive disorders of pregnancy, which can endanger the lives of pregnant women. These findings were published as a thesis in the American Society of Hematology’s journal ‘Blood’ in 2015.

RPL involving repeated miscarriages is also a clinical manifestation of antiphospholipid syndrome. As previously mentioned, the cause of RPL is unknown in over half of cases, however the association between this neo-self antibody and RPL had not been investigated. This research group hypothesized that the neo-self antibody could be connected to RPL in cases with unexplained causes.

With this in mind, blood samples were collected from RPL patients across five university hospitals (Kobe University, University of Toyama, Okayama University, The University of Tokyo, and Hyogo Medical University), and the samples were tested for neo-self antibodies at RIMD. For the first time in the world, the research group conducted this clinical study to illuminate the association between RPL and the neo-self antibody.

Research Findings

This study was led by Kobe University, which is putting a lot of effort into RPL research, and involved testing for neo-self antibodies with the consent of outpatient couples affected by RPL at five university hospitals nationwide. At the same time, a detailed examination into the cause of RPL in each case was carried out. This included testing for thyroid disorders, a chromosome analysis of each couple, and blood tests to investigate conditions that make blood clots form easily, such as the presence of antiphospholipid antibodies. Also, tests were carried out on the couples for genetic complexes that are associated with susceptibility to various diseases, such as Human Leukocyte Antigen (HLA) Class II. (For example, it is known that those with HLA-DR4 are prone to RPL).

The neo-self antibody testing method used in the study is a patented technology developed by this research group. This method involves producing cells where the complexes produced by β2-glycoprotein I (a protein that is believed to be targeted by the antibody that causes antiphospholipid syndrome) and HLA Class II (the HLA type that increases susceptibility to antiphospholipid syndrome) are present on the cell surface. A reaction is then conducted between the complexes and the patient’s blood to detect antibodies (neo-self antibodies), which bind to the complexes on the cell surface.

First of all, 208 women who did not have RPL and had previously given birth to healthy babies were tested for neo-self antibodies to establish normal levels. Subsequently, it was found that 52 (23%) out of 227 patients with RPL tested positive for the neo-self antibody.

The results of the tests carried out to determine the causes of RPL were evaluated. The neo-self antibody was the factor with the highest frequency compared to all other factors that were tested, including uterine issues (such as malformation and myomas), thyroid dysfunction, and chromosomal abnormalities in each partner. This indicts the possibility that this neo-self antibody is a major cause of RPL. Even after testing for common RPL causes, the cause could not be determined in around half of the patients (121 women). However, 24 (20%) of the 121 women with unexplained RPL were found to test positive for only the neo-self antibody (Figure 1). In particular, many who tested negative for antiphospholipid antibody criteria tested positive for the neo-self antibody (Figure 2).

When neo-self antibody positive women with RPL were compared with those RPL patients who tested negative, it was found that the frequency of those who had the HLA-DR4 gene, which predisposes the patient to RPL, was higher in neo-self antibody positive women than in negative women. Currently, it is unclear as to why those with HLA-DR4 are prone to RPL. It is hoped that this study’s discoveries can serve as a key to understanding the reason.

By investigating the neo-self antibody, the researchers were able to illuminate the onset mechanism of RPL, in particular the onset mechanism of the disorder in some unexplained cases. This could lead to a solution for Japan’s low birthrate and aging population issues.

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