Role of macrophage scavenger receptors in hepatic granuloma formation in mice

Abstract

In mice homozygous for the gene mutation for type I and type II macrophage scavenger receptors (MSR-A), MSR-A-/-, the formation of hepatic granulomas caused by a single intravenous injection of heat-killed Corynebacterium parvum was delayed significantly for 10 days after injection, compared with granuloma formation in wild-type (MSR-A+/+) mice. In the early stage of granuloma formation, numbers of macrophages and their precursor cells were significantly reduced in MSR-A-/- mice compared with MSR-A+/+ mice. In contrast to MSR-A+/+ mice, no expression of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and interferon-gamma mRNA was observed in MSR-A-/- mice by 3 days after injection. Also in MSR-A-/- mice, uptake of C. parvum by Kupffer cells and monocyte-derived macrophages in the early stage of granuloma formation was lower and elimination of C. parvum from the liver was slower than in MSR-A+/+ mice. In the livers of MSR-A+/+ mice, macrophages and sinusoidal endothelial cells possessed MSR-A, but this was not seen in the livers of MSR-A-/- mice. In both MSR-A-/- and MSR-A+/+ mice, expression of other scavenger receptors was demonstrated. These data suggest that MSR-A deficiency impairs the uptake and elimination of C. parvum by macrophages and delays hepatic granuloma formation, particularly in the early stage.

Figure 1.

Changes in liver weight of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice.

Figure 2.

Infiltration and granuloma formation of F4/80⁺ macrophages (C-F), ER-MP20⁺ monocytic cells (A, B, G, H), and ER-MP58⁺ myeloid macrophage precursor cells (I, J) in the livers of homozygous mutant (MSR-A^−/−) (B, D, F, H, J) and wild-type (MSR-A^+/+) (A, C, E, G, I) mice after injection of C. parvum. A and B: At 1 day after injection, infiltration of ER-MP20⁺ monocytic cells in the liver is more marked in an MSR-A^+/+ mouse (A) than in an MSR-A^−/− mouse (B). C and D: At 3 days after injection, focal collections of F4/80⁺ macrophages and granuloma formation are seen in the liver of an MSR-A^+/+ mouse (C) but not in MSR-A^−/− mouse (D). E and F: At 10 days, hepatic granulomas are much more developed and larger in an MSR-A^+/+ mouse (E) than in an MSR-A^−/− mouse (F). G and H: At 7 days, ER-MP20⁺ cells in the hepatic granulomas are more numerous in an MSR-A^+/+ mouse (G) than in an MSR-A^−/− mouse (H). I and J: At 10 days, infiltration of ER-MP58⁺ cells in the liver is more marked in an MSR-A^+/+ mouse (I) than in an MSR-A^−/− mouse (J). A-I: Indirect immunoperoxidase method with F4/80 C-F, ER-MP20 (A, B, G, and H), and ER-MP58 (I and J). Magnification, ×200

Figure 3.

Changes in the number (A) and mean diameters (B) of granulomas in livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice.

Figure 4.

Changes in the number of F4/80⁺ macrophages per granuloma (A) and per 1 mm within (B) and outside (C) granulomas in livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice.

Figure 5.

Changes in the number of ER-MP20⁺ monocytic cells (A-C) and ER-MP58-⁺ myeloid macrophage precursor cells (D-F) per granuloma (A and D) and per 1 mm within (B and E) and outside (C and F) granulomas in livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice.

Figure 6.

[³H]thymidine labeling of F4/80⁺ cells within (A) and outside (B) granulomas in livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of three mice.

Figure 7.

Percentages of apoptotic cells in hepatic granulomas of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of three mice.

Figure 8.

Changes in the number of Thy-1.2⁺ T cells per granuloma (A) and per 1 mm within (B) and outside (C) granulomas in livers of thomozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice.

Figure 9.

Expression of IL-1, TNF-α, IFN-γ, MCP-1, M-CSF, GM-CSF, MSR-A, MARCO, macrosialin, and CD36 mRNA in the livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. The result from one of two similar experiments is shown.

Figure 10.

Changes in the number of F4/80⁺ macrophages ingesting gram-positive C. parvum in livers of homozygous mutant (MSR-A^−/−) and wild-type (MSR-A^+/+) mice after injection of C. parvum. Data are mean ±SD of five mice

Figure 11.

Immunohistochemical expression of various types of scavenger receptors during hepatic granuloma formation in homozygous mutant (MSR-A^−/−) (B, D, F, and H) and wild-type (MSR-A^+/+) (A, C, E, and G) mice at 10 days after injection of C. parvum. A and B: Macrophages within and outside granulomas and sinusoidal endothelial cells express immunoreactivity for 2F8 in MSR-A^+/+ mice (A) but not in MSR-A^−/− mice (B). C-F: Macrophages within and outside hepatic granulomas of MSR-A^+/+ and MSR-A^−/− mice are positive for ED31 (C and D) and FA/11 (E and F). G and H: Macrophages within and outside granulomas and sinusoidal endothelial cells express Fcγ II receptor in livers of MSR-A^+/+ (G) and MSR-A^−/− (H) mice. A-H: Indirect immunoperoxidase method with 2F8 (A and B), ED31 (C and D), FA/11 (E and F), and 2.4G2 (G and H). Magnification, ×200

Figure 12.

Shows in vitro uptake of C. parvum by peritoneal macrophages via scavenger receptors in the early stage of phagocytosis. A: Compared with MSR-A-expressing macrophages, the uptake of C. parvum by MSR-A-deficient macrophage was significantly reduced. B: MSR-A-expressing and MSR-A-deficient macrophages show no difference in uptake of nonopsonized C. parvum. Compared with untreated macrophages, macrophages with Fcγ II receptor blocking show significant reductions in uptake of opsonized C. parvum in both MSR-A^+/+ and MSR-A^−/− mice. □, untreated; ▪, blocked with 2.4G2. Data are mean ±SD of three assays.