Effects of ITGAM Genetic Variation on Mac-1-Mediated Functions of B Cells
Abstract
Lupus is a chronic, life-changing disease that can affect the whole body. It is hard to diagnose, but overall more women than men get lupus and African-Americans, Asians, and Hispanics are more likely to get lupus than Caucasians. The course of lupus is hard to predict, but the most obvious problem that develops is an overactive immune system. This causes certain blood cells called B cells to make antibodies that attack the body instead of infections, the kidneys being the most often affected. Steroids and drugs used to treat cancer are the main therapies for lupus, but there is still no cure for the disease and more effective drugs are badly needed. Why some people get lupus and others do not is not known, but studies of families with lupus indicate the disease is inherited. Larger studies comparing thousands of healthy people to thousands of lupus patients have linked lupus to changes in DNA that codes for proteins needed for correct immunity. Unfortunately, whether these changes in DNA actually affect the functions of the DNA or the proteins it makes, and if and how these changes in DNA make it more likely that a person gets lupus, is not known. Until these two questions are answered lupus will remain hard to diagnose and hard to treat, and we will remain far from a cure. To answer these questions we will study the impact of two small changes in DNA that are known to be found more often in lupus patients than in healthy people. Both of these DNA changes happen within a gene, called ITGAM, that makes a protein called CD11b. CD11b pairs up with another protein made by another gene and together the two proteins form a receptor, called Mac-1, that is expressed on the surface of blood cells. Presumably, if a person inherits DNA with a change in the ITGAM gene then the CD11b protein it makes might be abnormal. The abnormal CD11b then might not pair up properly with its partner and be unable to make a correct Mac-1 receptor, or it could make a Mac-1 receptor that does not work correctly. Both situations could affect blood cells that express Mac-1 in a way that causes lupus. That is the scenario we are testing in our experiments. What does Mac-1 usually do? When Mac-1 on the surface of a blood cell binds to certain molecules outside the cell, it sends a message from outside to inside the cell instructing it to react. If Mac-1 binds to bacteria, this reaction can be the production and release of molecules that cause inflammation and fight off the infection, or if Mac-1 binds to the lining of a blood vessel, this reaction can cause a change in the shape of the cell, increase its stickiness, and help it crawl along the blood vessel. In both cases part of the cell s reaction to Mac-1 binding molecules outside the cell is to move more Mac-1 receptors to the place where the molecules were initially bound -- a process called clustering. Interestingly, when other kinds of receptors on blood cells bind to other kinds of molecules, this can cause changes inside the cell that activate Mac-1. This is appropriately called inside-out signaling. Inside-out and outside-in signaling allows Mac-1 to control blood cell functions that keep us healthy. We predict that changes in ITGAM DNA change CD11b and thus the signaling ability and movement of Mac-1, leading to abnormal cell responses that cause lupus. We predict that this problem is especially evident for B cells since Mac-1 on B cells helps them stick to the blood vessel walls, helps them move, turns down the strength of their signaling, and helps them make antibodies. In lupus patients B cells that express Mac-1 are known to be present in abnormally high numbers, but the function of Mac-1 on these cells and the impact of ITGAM DNA changes on these cells are not known. Two changes in ITGAM DNA known to be linked to lupus, one that changes the outside of CD11b and one that changes the inside of CD11b, have been shown to change the reactions and functions of some blood cells. We want to under
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1810631
Entities
People
- Alexander J. Szalai
Organizations
- United States Army
- University of Alabama at Birmingham