Estrogen decreases expression of chemokine receptors, and suppresses chemokine bioactivity in murine monocytes

Problem: We propose that the ability of estrogen exposure to increase the probability of a woman developing breast cancer may be related to decreased chemokine activity and suppression of immune surveillance in mammary tissue. The present study was conducted to determine whether estrogen could decrease monocyte bioactivity through alteration of chemokine receptor expression. Method of study: We examined the effect of estrogen and tamoxifen on the expression of the chemokine receptors CCR2 and CXCR3 on murine monocytes treated in culture and in vivo. Effects of estrogen on chemokine activation of monocytes were also evaluated. Results: Estrogen and tamoxifen significantly decreased expression of CCR2 and, to a lesser extent, CXCR3 on murine monocytes. Estrogen decreased chemotaxis of monocytes towards MCP-1/JE. The chemokines MCP-1/JE and MIP-1α were unable to evoke increases in intracellular calcium in murine monocytes treated with estrogen, alone or in combination with tamoxifen. Conclusions: Our results show that estrogen suppresses the ability of monocytes to respond to certain chemokines, suggesting that estrogen exposure might decrease immune surveillance in tissues where the action of specific chemokines is involved.