Epidermal Growth Factor Receptor (EGFR) Signaling Is a Key Mediator of Hormone-Induced Leukocyte Infiltration in the Pubertal Female Mammary Gland

Abstract

It is well documented that macrophages and eosinophils play important roles in normal murine pubertal mammary gland development. Although it is accepted that estrogen (E) and progesterone (P) are key players in mammary gland development, the roles these hormones might play in regulating the actions of leukocytes in that process is an understudied area. We show here that P and E, respectively, induce unique, but overlapping, sets of proinflammatory and angiogenic cytokines and chemokines, in the pubertal female BALB/c mammary gland, as well as induce infiltration of macrophages and eosinophils to the mammary periepithelium. This extends earlier studies showing P induction of proinflammatory products in pubertal and adult mammary epithelial organoids and P-induced in vivo infiltration of leukocytes to the adult mammary periepithelium. Importantly, epidermal growth factor receptor-signaling, which is likely mediated by amphiregulin (Areg), a downstream mediator of E and P, is both necessary and sufficient for both E- and P-induced recruitment of macrophages and eosinophils to the pubertal mammary periepithelium. We further show that receptor activator of nuclear factor κB ligand (RANKL), although not sufficient of itself to cause macrophage and eosinophil recruitment, contributes to an optimal response to P. The potency of Areg is highlighted by the fact that it is sufficient to induce macrophage and eosinophil recruitment at levels equivalent to that induced by either E or P. Our finding of a dominant role for Areg in hormonally induced leukocyte recruitment to the pubertal mammary gland parallels its dominance in regulating ductal outgrowth and its role in P-induced proliferation in the pubertal gland.

Role of Prolactin in Promotion of Immune Cell Migration into the Mammary Gland

“…Until now, recruitment has been attributed to effects of estrogen on epidermal growth factor receptor expression and the production of eotaxin [56]. Demonstration that prolactin directly stimulates production of a chemoattractant for eosinophils suggests either an estrogen-independent mechanism or, since estrogen elevates prolactin [57] that the effects of estrogen on recruitment of eosinophils could be via prolactin.…”

Interleukin-33 in Tissue Homeostasis, Injury, and Inflammation

“…The cytokines IL-4, IL-5 and IL-13, the epithelial growth factor amphiregulin, and eosinophil and AAM infiltration are all necessary for normal ductal outgrowth (Aupperlee et al, 2014; Colbert et al, 2005; Khaled et al, 2007); all of these findings are consistent with a role for ILC2s, which promote adipose tissue eosinophils and AAM (Molofsky et al, 2013b), produce a majority of tissue IL-5 and IL-13 (Nussbaum et al, 2013), and are a source of amphiregulin (Monticelli et al, 2011). Definitive studies, including the potential role of mammary gland IL-33, ILC2s, and Tregs, are needed.…”

Functions of tissue-resident eosinophils

“…Branching of the maturing ductal tree is shaped by soluble mediators and cell–cell interactions provided by the surrounding stroma, which positively or negatively regulate the growth and shape of proliferating ducts. Alternatively activated M2 macrophages and eosinophils are prominent cellular constituents of the mammary gland stroma and are implicated in regulating elongation and branching, respectively, of the ductal tree 98,99 . The influx of eosinophils into the mammary gland depends on the local production of eotaxins 100,101 , and eotaxin 1-deficient mice (which have decreased numbers of mammary gland eosinophils) exhibit defective ductal branching 99 .…”