Macrophages polarize into functionally divergent phenotypes - M1 and M2 - which express distinct receptors. These cells are known to express complement receptors, including CR1, CR3, and CR4. However, whether these complement receptors are differentially expressed on M1 and M2 macrophages is not yet known. Herein, we have examined the expression of CR1 to CR4 on murine bone marrow-derived M1 (stimulated with IFN-γ or LPS) and M2 (stimulated with IL-4 or IL-4 + IL-13) macrophages. We show that M1 cells exhibit increased expression of CR1/2, whereas M2 cells display the higher expression of CR4; CR3 is equally expressed on both the phenotypes. Thus, M1 cells are CR1/2⁺CR4⁺, and M2 are CR1/2⁻CR4⁺. Functional probing of these cells for their phagocytic ability indicates that M1 cells, which express higher CR1/2, internalize a significantly greater number of C3b-opsonized erythrocytes. Both M1 and M2 cells, on the other hand, internalize iC3b-opsonized erythrocytes to a similar extent. Interestingly, the phagocytic receptor involved in phagocytosis of iC3b-opsonized erythrocytes is only CR3 with no contribution of CR4. We, thus, propose that complement receptor expression can be used in combination with the expression of other known polarization markers to better locate a macrophage along its phenotypic spectrum.

巨噬细胞分化为功能不同的表型——M1 和 M2——它们表达不同的受体。已知这些细胞表达补体受体，包括 CR1、CR3 和 CR4。然而，这些补体受体是否在 M1 和 M2 巨噬细胞上差异表达尚不清楚。在此，我们检查了 CR1 到 CR4 在鼠骨髓来源的 M1（用 IFN-γ 或 LPS 刺激）和 M2（用 IL-4 或 IL-4 + IL-13 刺激）巨噬细胞上的表达。我们发现 M1 细胞表现出增加的 CR1/2 表达，而 M2 细胞表现出更高的 CR4 表达；CR3 在两种表型上的表达相同。因此，M1 细胞是 CR1/2 ⁺ CR4 ⁺，而 M2 是 CR1/2 ⁻ CR4 ⁺. 对这些细胞吞噬能力的功能性探测表明，表达更高 CR1/2 的 M1 细胞内化了显着更多的 C3b 调理红细胞。另一方面，M1 和 M2 细胞以相似的程度内化 iC3b 调理的红细胞。有趣的是，参与 iC3b 调理红细胞吞噬作用的吞噬受体仅为 CR3，没有 CR4 的贡献。因此，我们建议补体受体表达可以与其他已知极化标记的表达结合使用，以更好地沿其表型谱定位巨噬细胞。