Sex Hormone Receptors

Androgen and estrogen receptors are expressed in almost all the cells, including cells from the immune system, heart, and liver (Chaudry et al., 2003; Orshal and Khalil, 2004). Two major subtypes of estrogen receptors (ERs) (i.e., ER-a and ER-ß) have been identified. Furthermore, several subtypes of ER-a, such as ER-aA, ER-aC, ER-aE, and ER-aF, and of ER-ß, such as ER-ß1, ER-ß2, ER-ß4, and ER-ß5, have been described (Kos et al., 2002; Orshal and Khalil, 2004). Although some studies suggest that ERa promotes the protective effects of estrogen, others have shown that ER-ß is more critical for the beneficial effect of estrogen (Case and Davison, 1999; Kos et al., 2002; Pare et al., 2002; Scobie et al., 2002; Orshal and Khalil, 2004). A recent study showed that ER-a is essential for thymic and splenic development in males, whereas expression of ER-ß is required for estrogen-mediated thymic cortex atrophy and thymocyte phenotypic shift in females (Erlandsson et al., 2001). Previous studies have demonstrated that B-cell lymphopoiesis is normal in female ER-a-disrupted mice (Smithson et al., 1998), suggesting that ER-ß might be responsible for regulating B-cell formation in bone marrow (Kincade et al., 2000). The overall distribution of AR and ER expression was not different in T cells of male and female animals with and without trauma. Recent findings suggested that the T-cell expression of ER-a and ER-ß in response to trauma-hemorrhage is different (Samy et al., 2000; Samy et al., 2001; Samy et al., 2003). These findings have shown that while ER-a expression did not change after trauma-hemorrhage, the expression of ER-ß was significantly decreased in the proestrus females after trauma-hemorrhage. Such alterations in ER-ß expression may contribute to the observed changes in T-cell functions.

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