Effects of raloxifene, a selective estrogen receptor modulator, on thymus, T cell reactivity, and inflammation in mice.

Raloxifene is a selective estrogen receptor modulator approved for prevention of osteoporosis in postmenopausal women. It is selective by virtue of having estrogen agonistic effects in bone, vessels, and blood lipids, while it is antagonistic with mammary and uterine tissue. The aim of the study was to examine whether the raloxifene analogue LY117018 (LY) has estrogenic effects on the thymus, T cell responsiveness, and inflammation. Oophorectomized normal mice were treated with subcutaneous injections of equipotent antiosteoporotic doses of LY (3 mg/kg) and 17beta-estradiol (E2) (0.1 mg/kg) or vehicle as controls. Effects on thymus were studied by analyses of thymus weight, cellularity, and CD4 and CD8 phenotype expression and histology, while inflammation was determined as T-cell-mediated delayed-type hypersensitivity (DTH) and granulocyte-mediated footpad swelling. LY lacked the suppressive properties of E2 on DTH and granulocyte-mediated inflammation. Furthermore, LY induced only minor thymus atrophy compared with E2 and did not, in contrast to E2, alter the thymic CD4/CD8 phenotypes. These results clearly demonstrate that raloxifene principally lacks the modulatory effects of estrogen on T cell responsiveness and inflammation. Our data are discussed in the context of recent findings in estrogen receptor biology and also with respect to estrogen-mediated alteration of autoimmune rheumatic diseases. Copyright 2000 Academic Press.