Tissue-specific expression of IgG receptors by human macrophages ex vivo

Abstract

Recently it was discovered that tissue-resident macrophages derive from embryonic precursors, not only from peripheral blood monocytes, and maintain themselves by self-renewal. Most in-vitro studies on macrophage biology make use of in-vitro cultured human monocyte-derived macrophages. Phagocytosis of IgG-opsonized particles by tissue-resident macrophages takes place via interaction with IgG receptors, the Fc-gamma receptors (FcγRs). We investigated the FcγR expression on macrophages both in-vivo and ex-vivo from different human tissues. Upon isolation of primary human macrophages from bone marrow, spleen, liver and lung, we observed that macrophages from all studied tissues expressed high levels of FcγRIII, which was in direct contrast with the low expression on blood monocyte-derived macrophages. Expression levels of FcγRI were highly variable, with bone marrow macrophages showing the lowest and alveolar macrophages the highest expression. Kupffer cells in the liver were the only tissue-resident macrophages that expressed the inhibitory IgG receptor, FcγRIIB. This inhibitory receptor was also found to be expressed by sinusoidal endothelial cells in the liver. In sum, our immunofluorescence data combined with ex-vivo stainings of isolated macrophages indicated that tissue-resident macrophages are remarkably unique and different from monocyte-derived macrophages in their phenotypic expression of IgG receptors. Tissue macrophages show distinct tissue-specific FcγR expression patterns.

Fig 1. Red pulp macrophages express FcγRIIA, and FcγRIII.

Immunofluorescence stainings of spleen sections with CD163 and (A) CD68 and CD19; (B) FcγRI and FcγRIIB/C; (C) FcγRII; (D) FcγRIIA and FcγRIIB/C (E) FcγRIII and CD19. Magnification 10x. Scale bars equal 100 μm. Figures are representative of n = 3 spleens from different donors. We have previously shown immunofluorescent stainings of human spleen tissue.¹⁸ Images in this figure are from sections from a different human spleen.

Fig 2. Kupffer cells express FcγRIIA, FcγRIIB and FcγRIII.

Immunofluorescence stainings of liver sections with CD163 and (A) CD68 and FcγRIIB/C; (B) VECadherin and FcγRIIB/C; (C) FcγRI; (D) FcγRII; (E) FcγRIIA and FcγRIIB/C; (F) FcγRIII. Magnification 20x. Scale bars equal 50 μm. Figures are representative of n = 2 livers from different donors.

Fig 3. Lung macrophages express FcγRI and FcγRII.

Immunofluorescence stainings of lung sections with CD163, Hoechst and (A) CD68; (B) VECadherin; (C) FcγRI; (D) FcγRII; (E) FcγRIIA; (F) FcγRIII. Magnification 20x. Scale bars equal 50 μm. Figures are representative of n = 3 lungs from different donors. In (A) alveolar spaces are indicated with grey dashed lines.

Fig 4. FcγR expression by macrophages from different tissues.

Expression of (A) FcγRI, (B) FcγRIIA (MoAb IV.3), (C) FcγRIIB/C (MoAb 2B6), individuals encoding FCGR2C-ORF are indicated in red, and (D) FcγRIII by monocyte-derived macrophages cultured in the presence of GM-CSF, n = 9–32, and M-CSF, n = 9–39, by bone marrow macrophages, n = 14, red pulp macrophages, n = 83, Kupffer cells, n = 5, and alveolar macrophages, n = 5, determined by flow cytometry. For the cultured macrophages, individuals encoding FCGR2C-ORF were excluded from analysis. Data shown are median fluorescence intensity, corrected for the proper isotype control. For FcγRIIB/C expression, the levels on BM macrophages versus Kupffer cells from liver were nearly significant, p = 0.058. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001, ns = not significant.