Mammary macrophages are highly plastic and developmentally heterogeneous innate immune cells that play pivotal roles in maintaining tissue homeostasis, regulating mammary development, and responding to pathological stimuli. While traditionally thought to originate primarily from postnatal bone marrow–derived monocytes, recent studies have revealed that embryonic macrophages derived from the yolk sac and fetal liver not only colonize the mammary gland before birth but also dominate the stromal compartment in adult mammary tissue, exhibiting unique tissue-resident properties and high phagocytic activity.
At the physiological level, these macrophages participate in the transport and secretion of trace nutrients such as iron into milk via a non-canonical leukocyte-assisted pathway, bypassing the classical transferrin receptor–mediated route. During mammary development, they are recruited and polarized by epithelial cell–derived signals (e.g., the Il4–Stat6 axis induced by Mcam deficiency), and in turn secrete non-canonical ligands such as Wnt5a to regulate epithelial cell proliferation, differentiation, and ductal morphogenesis. However, this remarkable plasticity also renders them susceptible to "hijacking" within the disease microenvironment — for instance, being reprogrammed into tumor-promoting phenotypes in breast cancer. Therefore, a deeper understanding of the heterogeneous origins, metabolic profiles, and bidirectional crosstalk between mammary macrophages and their microenvironment is not only essential for deciphering the complexity of mammary biology, but also provides critical targets for developing novel nanoparticle-based drug delivery strategies for mastitis treatment, nutritional fortification, and tumor immunotherapy.
Reference 1
Source: Mammary Leukocyte-Assisted Nanoparticle Transport Enhances Targeted Milk Trace Mineral Delivery (IF=14.1, Q1)
Macrophage Depletion Method:
Clodronate liposomes (0.15–0.2 mL/25 g) were administered via intravenous injection to lactating mice to deplete macrophages from both the circulation and the mammary gland. Control liposomes were used to evaluate and exclude any effects attributable to the liposome vehicle itself. At 24, 48, and 72 hours post-injection, flow cytometry was performed to quantify mammary-resident macrophages, and complete blood counts were conducted to monitor blood monocyte levels, thereby confirming the efficiency of macrophage depletion. Clodronate liposomes (Cat: 40337ES08) and control liposomes (Cat: 40338ES05) were purchased from Shanghai Yeasen Biotechnology Co., Ltd.
Results:
Within 72 hours of clodronate liposome treatment, macrophages in both the circulation and mammary glands of lactating mice were successfully depleted, with gradual recovery observed beyond the 72-hour mark (Fig. S6). This confirmed a clean 72-hour experimental window for all downstream assays (Fig. S6a, b).
Reference 2
Source:
Mcam inhibits macrophage-mediated development of mammary gland through non-canonical Wnt signaling (IF=15.7, Q1)
Macrophage Depletion Method:
Four-week-old Mcam cKO mice (body weight ~13–15 g) were treated with clodronate liposomes (CL; 130–150 μL) every other day for one week, after which mammary tissues were harvested.
Results:
To confirm the mediating role of macrophages in the aforementioned functions, a rescue experiment was performed using clodronate liposomes (CL) to specifically deplete macrophages in both WT and cKO mice. Following CL injection, the percentage of macrophages was effectively reduced in both WT and cKO mice, as demonstrated by FACS analysis (see figure).
Reference 3
Source:
Fetal-derived macrophages dominate in adult mammary glands (IF=15.7, Q1)
Macrophage Depletion Method:
To deplete postnatally derived tissue-resident macrophages, 2-week-old C57BL/6N mice received cyclical treatment with anti-CSF1 antibody and clodronate (Fig. 2b). Subsequently, three doses of clodronate liposomes or control liposomes were administered via intravenous injection (i.v.) on postnatal days 15, 19, and 23 (50 μL per dose). Mice were sacrificed 1 day or 11 days after the final clodronate treatment.
Results:
One day after the final treatment (day 24), the numbers of total F4/80^Int and F4/80^Hi macrophages in the mammary glands of mice in the clodronate + anti-CSF1 treatment group (Clod + aCSF1) were significantly reduced compared with the control group (CO).
Reference 4
Source:
Macrophages maintain mammary stem cell activity and mammary homeostasis via TNF-α–Cdk1/Cyclin B1 axis (IF=6.5, Q1)
Macrophage Depletion Method:
Adult wild-type female mice (8–10 weeks old) were used for clodronate liposome (CL) and infliximab administration experiments. For macrophage depletion, adult mice weighing 18–20 g received intraperitoneal injections of 180–200 μL macrophage depletion agent per mouse, administered every other day for a total of 3 injections, after which mammary tissues were harvested. Flow cytometry (FACS) was used to assess macrophage depletion efficiency.
Results:
Fig. 1a: Immunofluorescence staining (F4/80 for macrophages, K14 for basal cells, K8 for luminal cells) visually demonstrates a marked reduction in macrophages in the CL group. Fig. 1b: FACS quantification of macrophage depletion efficiency (control group: 3.9±0.8% → CL group: 0.4±0.1%, ~90% depletion efficiency).
Related Product
|
Name |
Cat. No. |
Size |
|
40339ES05/08/10 |
2 + 2 mL |
|
|
Clodronate Liposomes(From Vrije Universiteit Amsterdam) |
40337ES05/08/10 |
2 mL/5 mL/10 mL |
|
Control Liposomes( PBS ) |
40338ES05/08/10 |
2 mL/5 mL/10 mL |