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Antibodies against macrophages that overlap in specificity with fibroblasts
Kidney International, Vol. 68 (2005), pp. 2400–2404
LETTERS TO THE EDITOR
Antibodies against macrophages that overlap in specificity with fibroblasts
REFERENCES 1. INOUE T, PLIETH D, VENKOV CD, et al: Antibodies against macrophages that overlap in specificity with fibroblasts. Kidney Int 67:2488–2493, 2005 2. MAZZUCCHELLI L: Protein S100A4: Too long overlooked by pathologists? Am J Pathol 160:7–13, 2002 3. ITO K, CHEN J, EL CHAAR M, et al: Renal damage progresses despite improvement of renal function after relief of unilateral ureteral obstruction in adult rats. Am J Physiol Renal Physiol 287:F1283–1293, 2004 4. LE HIR M, HEGYI I, CUENI-LOFFING D, et al: Characterization of renal interstitial fibroblast-specific protein 1/S100A4-positive cells in healthy and inflamed rodent kidneys. Histochem Cell Biol 123:335– 346, 2005 5. MARTINEZ DEL HOYO G, MARTIN P, ARIAS CF, et al: CD8alpha+ dendritic cells originate from the CD8alpha-dendritic cell subset by a maturation process involving CD8alpha, DEC-205, and CD24 upregulation. Blood 99:999–1004, 2002 6. KRUGER T, BENKE D, EITNER F, et al: Identification and functional characterization of dendritic cells in the healthy murine kidney and in experimental glomerulonephritis. J Am Soc Nephrol 15:613–621, 2004
To the Editor: In the June issue of Kidney International, a Technical Note is devoted to the discrimination between fibroblasts and macrophages in inflamed renal tissue [1]. The authors examined the expression of macrophage antigens in putative fibroblasts identified by expression of FSP1. FSP1+ cells expressed macrophage antigens CD45, Mac-1, Mac-2, Mac-3, CD68, and MHC class II, but not F4/80. They conclude that among the markers tested F4/80 is the only one specific for macrophages in the inflamed mouse kidney since the others are also expressed in FSP1+ fibroblasts. We would like to question two assumptions of the authors. First, a survey of the literature casts serious doubts on the specificity of FSP1 (also known as S100A4) for fibroblasts. FSP1/S100A4 has been found in various cell types [2]. Specifically in the kidney, after ureter obstruction, a fraction of FSP1/S100A4+ cells were identified as inflammatory cells [3]. In inflamed kidneys we observed colocalization of FSP1/S100A4 with leukocyte markers in cells that clearly displayed the morphology of mononuclear cells [4]. Second, a subpopulation of dendritic cells expresses F4/80 [5]. Expression of F4/80 has been demonstrated in renal dendritic cells [6]. With these facts in mind we propose an interpretation of the data of Inoue et al [1], which diverge from that of the authors: At least a fraction of FSP1+ cells in the fibrotic kidney are infiltrating leukocytes expressing CD45, Mac-1, Mac-2, Mac-3, CD68, and MHC class II. Therefore, the suitability of FSP1 and of F4/80 as markers for fibroblasts and for macrophages, respectively, must be questioned. MICHEL LE HIR and BRIGITTE KAISSLING
Zurich, Switzerland Correspondence to Michel Le Hir, Department of Anatomy, University of Zurich, Zurich, Switzerland. E-mail: [email protected]
C
2005 by the International Society of Nephrology
Reply from the Authors We thought our paper in a recent issue of Kidney International might stimulate comment on the identification of macrophages and fibroblasts [1]. Our correspondents raise two concerns. It is easier to address the second complaint first: our failure to distinguish dendritic cells from macrophages. This distinction was not our immediate point. We acknowledge dendritic cells, like macrophages, have antigen-presenting properties and may be identified by F4/80 antibodies. FSP1, or S100A4, is specific for fibroblasts in normal mice by genetic and protein criteria ([1–3]; reference [7] in [1]). Our experience in rats is limited, but we have no reason to feel its specificity is different than mice. Two experiments being readied for publication in human tissue also support FSP1 specificity in fibroblasts. Nevertheless, our correspondents’ second criticism cites several publications that question this specificity. In one reference, they argue FSP1 is expressed in inflammatory cells [3]. Although S100A4 antibody was used in rat renal tissue, the methods defined stained fibroblasts as “spindle-shaped” cells and stained leukocytes as “rounded” cells. There was no double-staining to support this assumption. Some fibroblasts may look ‘round’ depending on their orientation in tissue sections, making a ‘shape’ criterion unreliable. Our correspondents also assert in their own paper that FSP1 is expressed by rat leukocytes [4]. Although doublestaining techniques were employed, these authors also
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LETTERS TO THE EDITOR
Antibodies against macrophages that overlap in specificity with fibroblasts
REFERENCES 1. INOUE T, PLIETH D, VENKOV CD, et al: Antibodies against macrophages that overlap in specificity with fibroblasts. Kidney Int 67:2488–2493, 2005 2. MAZZUCCHELLI L: Protein S100A4: Too long overlooked by pathologists? Am J Pathol 160:7–13, 2002 3. ITO K, CHEN J, EL CHAAR M, et al: Renal damage progresses despite improvement of renal function after relief of unilateral ureteral obstruction in adult rats. Am J Physiol Renal Physiol 287:F1283–1293, 2004 4. LE HIR M, HEGYI I, CUENI-LOFFING D, et al: Characterization of renal interstitial fibroblast-specific protein 1/S100A4-positive cells in healthy and inflamed rodent kidneys. Histochem Cell Biol 123:335– 346, 2005 5. MARTINEZ DEL HOYO G, MARTIN P, ARIAS CF, et al: CD8alpha+ dendritic cells originate from the CD8alpha-dendritic cell subset by a maturation process involving CD8alpha, DEC-205, and CD24 upregulation. Blood 99:999–1004, 2002 6. KRUGER T, BENKE D, EITNER F, et al: Identification and functional characterization of dendritic cells in the healthy murine kidney and in experimental glomerulonephritis. J Am Soc Nephrol 15:613–621, 2004
To the Editor: In the June issue of Kidney International, a Technical Note is devoted to the discrimination between fibroblasts and macrophages in inflamed renal tissue [1]. The authors examined the expression of macrophage antigens in putative fibroblasts identified by expression of FSP1. FSP1+ cells expressed macrophage antigens CD45, Mac-1, Mac-2, Mac-3, CD68, and MHC class II, but not F4/80. They conclude that among the markers tested F4/80 is the only one specific for macrophages in the inflamed mouse kidney since the others are also expressed in FSP1+ fibroblasts. We would like to question two assumptions of the authors. First, a survey of the literature casts serious doubts on the specificity of FSP1 (also known as S100A4) for fibroblasts. FSP1/S100A4 has been found in various cell types [2]. Specifically in the kidney, after ureter obstruction, a fraction of FSP1/S100A4+ cells were identified as inflammatory cells [3]. In inflamed kidneys we observed colocalization of FSP1/S100A4 with leukocyte markers in cells that clearly displayed the morphology of mononuclear cells [4]. Second, a subpopulation of dendritic cells expresses F4/80 [5]. Expression of F4/80 has been demonstrated in renal dendritic cells [6]. With these facts in mind we propose an interpretation of the data of Inoue et al [1], which diverge from that of the authors: At least a fraction of FSP1+ cells in the fibrotic kidney are infiltrating leukocytes expressing CD45, Mac-1, Mac-2, Mac-3, CD68, and MHC class II. Therefore, the suitability of FSP1 and of F4/80 as markers for fibroblasts and for macrophages, respectively, must be questioned. MICHEL LE HIR and BRIGITTE KAISSLING
Zurich, Switzerland Correspondence to Michel Le Hir, Department of Anatomy, University of Zurich, Zurich, Switzerland. E-mail: [email protected]
C
2005 by the International Society of Nephrology
Reply from the Authors We thought our paper in a recent issue of Kidney International might stimulate comment on the identification of macrophages and fibroblasts [1]. Our correspondents raise two concerns. It is easier to address the second complaint first: our failure to distinguish dendritic cells from macrophages. This distinction was not our immediate point. We acknowledge dendritic cells, like macrophages, have antigen-presenting properties and may be identified by F4/80 antibodies. FSP1, or S100A4, is specific for fibroblasts in normal mice by genetic and protein criteria ([1–3]; reference [7] in [1]). Our experience in rats is limited, but we have no reason to feel its specificity is different than mice. Two experiments being readied for publication in human tissue also support FSP1 specificity in fibroblasts. Nevertheless, our correspondents’ second criticism cites several publications that question this specificity. In one reference, they argue FSP1 is expressed in inflammatory cells [3]. Although S100A4 antibody was used in rat renal tissue, the methods defined stained fibroblasts as “spindle-shaped” cells and stained leukocytes as “rounded” cells. There was no double-staining to support this assumption. Some fibroblasts may look ‘round’ depending on their orientation in tissue sections, making a ‘shape’ criterion unreliable. Our correspondents also assert in their own paper that FSP1 is expressed by rat leukocytes [4]. Although doublestaining techniques were employed, these authors also
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