Enzyme-Activating Antibodies Revealed As Marker for Severe Rheumatoid Arthritis
News May 30, 2013
In a series of lab experiments designed to unravel the workings of a key enzyme widely considered a possible trigger of rheumatoid arthritis, researchers at Johns Hopkins have found that in the most severe cases of the disease, the immune system makes a unique subset of antibodies that have a disease-promoting role.
Reporting in the journal Science Translational Medicine online May 22, the Johns Hopkins team describes how it found the novel antibodies to peptidylarginine deiminase 4, or PAD4, in blood samples from people with aggressive inflammation and connective tissue damage.
Researchers say the presence of so-called PAD3/PAD4 cross-reactive autoantibodies could serve as the basis for the first antibody-specific diagnostic test to distinguish those with severe rheumatoid arthritis from those with less aggressive forms of the disease.
“Identifying early on a subset of patients with severe rheumatoid arthritis could benefit their health, as these patients could start aggressive drug therapy immediately and find the most effective treatment option,” says senior study investigator Antony Rosen, M.D. Rosen, director of rheumatology and the Mary Betty Stevens Professor at the Johns Hopkins University School of Medicine, says that a third, or 1 million of the more than 3 million Americans – mostly women – estimated to have rheumatoid arthritis have an aggressive form of the disease.
In the study, the antibodies were present – in 18 percent of 44 fluid samples from one research collection and in 12 percent of another collection of 194 – but only in people with severe cases of rheumatoid arthritis. Past research shows that those with the most aggressive disease are less likely to respond to anti-inflammatory treatments with steroids and other drugs.
An examination of patients’ medical records revealed that 80 percent of patients with the antibody saw their disease worsen over the previous year, while only 53 percent without the antibody showed disease progression. In comparing average scores of disease-damaged joints, researchers found that those with the antibody had an average deterioration in joints and bones by a score of 49. Those without the antibody had an average degradation in their score of 7.5, indicating much milder disease.
In a related finding, the Johns Hopkins team also uncovered how the PAD3/PAD4 cross-reactive auto-antibodies might contribute to more severe, erosive disease in rheumatoid arthritis. The team performed a series of experiments to gauge the antibodies’ effects on PAD4 in response to varying cell levels of calcium, on which PAD enzymes depend.
Lab experiments showed that the antibodies greatly increase PAD4 enzyme function at the low levels of calcium normally present in human cells. Results showed that PAD4 activity was 500 times greater in the presence of antibodies than when they were absent. Tests of the antibody and enzymes’ chemical structures later showed that the antibodies bind to PAD4 in the same region as calcium, suggesting to researchers that the antibodies might be substituting for calcium in activating the enzyme.
According to Rosen, the series of experiments, which took two years to complete, represents the first evidence of an antibody having a direct role in generating the targets of the immune response, or auto-antigens, in rheumatoid arthritis.
“Our results suggest that drugs inhibiting the PAD4 enzyme may have real benefit in patients with severe rheumatoid arthritis and represent an important field of study for investigating new and alternative treatments,” says lead study investigator and biologist Erika Darrah, Ph.D.
Darrah says the team next plans long-term monitoring of arthritis sufferers to find out when the antibody first appears in the blood, and when intervention may have maximum impact in preventing or stalling disease progression. The team also plans further experiments to see if the antibody is taking control of the chemical pathways normally used by other cell proteins to control PAD4 sensitivity to calcium.
Tiny “Tornado” Boosts Performance of Electrospray Ionization Mass SpectrometryNews
Known as Dry Ion Localization and Locomotion (DRILL), the new device creates a swirling flow that can separate electrospray droplets depending on their size.READ MORE
Large-Scale Production of Living Brain Cells Enables Entirely New ResearchNews
After performing a biopsy on the patient, the skin cells are transformed into brain cells that effectively imitate the disease and the age of the patient.READ MORE
Innate Reaction of Hematopoietic Stem Cells to Severe InfectionsNews
Researchers at the University of Zurich have shown for the first time that hematopoietic stem cells detect infectious agents themselves and begin to divide, without signals from growth factors.READ MORE
Comments | 0 ADD COMMENT
EMBO Workshop: Integrating Systems Biology: From Networks to Mechanisms to Models
Apr 15 - Apr 17, 2018
EMBL Course: Transgenic Animals - Micromanipulation Techniques
Apr 10 - Apr 11, 2018
EMBO Practical Course: Extracellular Vesicles: From Biology to Biomedical Applications
Apr 09 - Apr 13, 2018