High levels of female hormones like estrogen have traditionally been thought harmful to women with lupus, based in part on the long-time belief by many that pregnancy is deleterious for women with lupus. Though hormones play a role in the immune response, researchers are exploring other possibilities to explain the female predominance of autoimmune diseases. These factors make it much more difficult to track inheritance of specific genes involved in an autoimmune disease than in other diseases that result from one gene acting with little or no environmental influence. One lead came out of the observation that during pregnancy a mother's immune system normally programmed to reject any foreign tissue tolerates the presence of a fetus, half of whose genetic make-up is from the father. These are the antigens on cell surfaces that enable the immune system to distinguish between the body's own cells and those that are foreign.
Scientists study why more women are affected than men.
Dr. Nelson found that certain HLA gene markers were more frequently dissimilar between mother and child in pregnancies in which the mother's RA improved. Without proposing a single specific mechanism, Nelson hypothesizes that the mother's immune response to the fetus may play a role in the improvement in RA during pregnancy. Recent research supported by the National Institute of Child Health and Human Development found that fetal cells could persist in the bloodstream of the mother for as long as 27 years after birth. The peak incidence of scleroderma in women is between the ages of 35 to 54, just after the childbearing years. Dr. Nelson's group is looking to see whether scleroderma which shares some features with graft vs. host disease, an immune reaction of a donor's transplanted cells to the tissues of the recipient of a bone marrow transplant is more frequent in women whose HLA types are more similar to that of their offspring.