One year ago, S. Louis Bridges, M.D., Ph.D., and colleagues published an important finding from the blood of patients with rheumatoid arthritis. They found increased expression of two genes for receptors on the surfaces of immune cells in the blood, and those increases corresponded to either presence of the disease — compared with controls — or with the severity of this autoimmune disorder.
This discovery is the foundation of a $1.8 million Department of Defense grant just awarded to Bridges and Chander Raman, Ph.D. They plan to uncover details about these changes that will help explain how rheumatoid arthritis leads to joint damage and why some patients develop painful and debilitating bone erosions.
Bridges, a University of Alabama at Birmingham professor of medicine and director of the Division of Clinical Immunology and Rheumatology, and Raman, a professor of medicine in the same division, combine the independent strengths of a clinician/researcher and a basic scientist.
In last year’s report, the receptor gene changes were found in pooled blood mononuclear cells from each patient. The first challenge of the new grant is to pinpoint which specific subsets of immune cells in the blood have those changes. To do this, single subpopulations of cells — one by one — will be subsetted using differential expression for 15 different markers.
“For a biological researcher, one of the biggest challenges is to solve the puzzle of disease,” Raman said. “Before, we could not easily subset these cells to get a clearer understanding of the immunopathology. Now we can ask, very clearly, what subsets of cells are involved?”
Continued advances in RNA sequencing and fluorescence-activated cell sorting allow such single-cell analysis, and this level of detail is crucial because the immune system — called “one of nature’s most fascinating inventions” by nobelprize.org — is also one of the most complex systems in biology.
The immune system is constantly on the alert for invaders like viruses and bacteria, and its control comes through extremely complicated interactions among many different immune cell types. As the cells either turn on an immune response or dampen that response to allow healing of damaged tissue, subsets of immune cell types are ‘talking’ to each other as ‘sender’ cells release signaling proteins that bind to receptors on the surfaces of ‘receiving’ cells. Those receptors in turn tell the nucleus of the receiving cell to activate specific genes, and those genes may go on to send a signal to other cells.
In autoimmune disorders like rheumatoid arthritis, regulation of the immune system has gone awry, and the immune system now attacks its own body. This mostly means the joints in rheumatoid arthritis, but can also include the skin, lungs, kidneys, heart, blood vessels and other organs.
The discovery by Bridges and colleagues last year was notable because the two genes they found make receptor subunits for the signaling protein interferon-gamma (IFN-γ). Other research has shown a pathogenic link between IFN-γ and autoimmunity, as evidenced by high levels of IFN-γ and IFN-γ receptors in the joint fluid of patients with rheumatoid arthritis and the beneficial effect of targeting IFN-γ in a select subset of patients who have systemic lupus erythematosus, another autoimmune disease. IFN-γ is also involved in multiple sclerosis.
Bridges and colleagues found that gene expression of IFN-γ receptor 1 was strongly associated with disease, and gene expression of IFN-γ receptor 2 was strongly associated with radiographic severity. After the first step in the new grant of identifying the subset(s) of cells showing increased expression of those two genes, Raman and Bridges will probe details of the signaling activation in those cells. They also will look into altered regulation by the cytokine interleukin-2.
The study will enroll patients with rheumatoid arthritis, patients with multiple sclerosis and healthy controls. The multiple sclerosis patients are for comparison and may lead to new discoveries for the role of IFN-γ in that disease. Patients and controls will donate two small vials of blood for the experiments.
The Department of Defense funding comes through its Congressionally Directed Medical Research Programs. These are targeted research funds added to the Department of Defense budget by Congress. In fiscal 2015, for example, $1.38 billion was targeted for 28 different diseases, injuries or medical issues that affect armed forces service members.
At UAB, Bridges holds the Anna Lois Waters Endowed Chair in Rheumatology.