Figure 3.

TNFα is an essential down-stream signal of LPS/TLR4 signaling on mammary alveolar macrophages mediating neutrophil recruitment. Mammary glands of lactating C57BL/6 and TNFα −/− mice were infused with 10 μg LPS. H&E staining of formalin-fixed mammary tissues 24 h after LPS inoculation (A−C). Massive recruitment of neutrophils into the alveolar space is seen in C57BL/6 mice (A and Fig. 6C) while no signs of inflammation are observed in TNFα −/− mice (B and inset B). Intramammary transfer of C57BL/6 macrophages into TNF −/− mice restored LPS-induced mammary inflammation (Fig. 3C) identically to that in C57BL/6 mice. Neutrophil recruitment to the mammary gland was assessed by the MPO assay (D). A significant difference in relative (LPS to PBS-challenged gland) MPO activity was observed in mammary glands of TNFα −/− mice after macrophage transfer compared with C57BL/6 and TNFα −/− mice. Data are mean and S.E., n ≥ 6/group and p values represent a comparison between groups using the Student t-test. Scale bars 50 μm (A, C and inset B), 200 μm (B). (A color version of this figure is available at www.vetres.org.)