The Thymus in Hemochromatosis Vincent J. Vigorita, MD, and Grover M. Hutchins, MD
Although iron in cases of hemochromatosis has been described in virtually everv organ, its presence in the thymus has only been rarely observed. While investigating all cases of hemochromatosis autopsied at The Johns Hopkins Hospital over the past decade, 4 adult cases in which the thymus was available for histologic study were examined in light of recent documentation of this organ's role in lymphopoiesis and secretory activity. Iron-containing moieties were found within both lymphocvtes and epithelial cells of these involuted thymic glands. The thvmic iron suggests either an uptake of iron moieties from the vascular pool or their synthesis within the cell itself. While the former mechanism provides evidence against the existence of an impermeable bloodthymus barrier, the latter supports the existence of a metabolicallv active gland with complex function. (Am J Pathol 93:661-666, 1978)
HEMOCHROMATOSIS is a disease of multiple causes in which iron deposition takes place in parenchymal cells throughout the body, which is usually associated with changes such as fibrosis in the liver.' Although its mechanism is not understood, the predilection of iron distribution for organs with exocrine and endocrine function is well known.2'3 The deposition of stainable iron in the anterior lobe of the pituitary, the zona glomerulosa of the adrenals, and the sweat glands of the skin suggests that even within certain organs and tissues there appears to be a preferential pattern. Herein we report 4 cases of iron involvement of ageinvoluted thymic glands in cases of secondary or exogenous hemochromatosis and suggest that the extent of iron observed indicates a predilection for the thymus similar to glandular components elsewhere in the body, perhaps a further indication of the complex secretory nature of the thymus. Materials and Methods All hemochromatosis cases in which autopsies w%-ere performed at The Johns Hopkins Hospital over the past decade were clinically and pathologically reviewed. (Hemochromatosis is defined as the parenchymal distribution of iron with associated tissue changes such as fibrosis or cirrhosis in the liver.') Four cases revealed identifiable, although age-involuted, thymic tissue. All histologic material was reviewed by light microscopy and sections stained by the Gomori iron reaction. Fragments of tissue which had been embedded in paraffin were reprocessed for electron microscopy. The severitx of iron in the From the Department of Pathology of The Johns Hopkins Medical Institutions. Baltimore. Marv and. Supported by Grant HL-14153 from the National Institutes of Health. Accepted for publication Julv 24, 1978. Address reprint requests to Dr. Grover M. Hutchins. Department of Pathology. The Johns Hopkins Hospital, Baltimore, MD 21205. 0002-9440/78/121 1 -0661S01 .00 661 0 1978 American Association of Pathologists
662
American Journal of Pathology
VIGORITA AND HUTCHINS
thymus as well as other tissues was graded on a scale of 0 to 4+, representing no involvement to severe involvement, respectively. Particular attention was given to the thymus to determine what cellular components were involved.
Results
The clinical information is reviewed in Table 1. In all cases there was a history of exogenous hemochromatosis with an underlying chronic anemia requiring multiple blood transfusions which reached massive proportions in 2 cases. Cirrhosis of the liver was present in all cases. The parenchymal distribution of iron was moderate to severe throughout, as tabulated. Although in all cases the thymus was age-involuted precluding a clear demarcation between medullary and cortical regions, iron was found throughout the remaining tissue but was restricted to intracytoplasmic localization (Figures 1 and 2). Whereas epithelial cells and macrophages were involved in all cases, endothelial cells and lymphocytes revealed iron by light microscopy in only Case 1, the most severely affected case (Table 2). Hassall's corpuscles showed positive staining in all but Case 1, in which no corpuscles were seen. Electron microscopy confirmed the intracellular, intracytoplasmic localization of iron. In all cases, iron deposition in epithelial cells and macrophages was more severe than in the other cellular components of the gland. Table 1-Patients Studied Age (yr) Race
1 72 Black
Sex Major clinical diagnosis
Male Refractory anemia
Cause of death Transfusions/years Cirrhosis Tissue iron Liver Pancreas
Case
Spleen Endocrine Thyroid Adrenals Parathyroid
Pituitary Stomach Kidneys Lungs CHF
=
4 70 Black Female
CHF 250 units/3 Severe
2 3 54 49 Black White Male Female Ethanolism Sideroblastic Folate-deficanemia ient megaloblastic anemia CHF Meningitis Few/3 Many/1 0 Early Severe
4+ 4+ 2+
2-3+ 2+ 3-4+
3-4+ 3+ 0-1+
3+ 3+ 3+
4+
2+ 0-1 + 2+ 2-3+ 2+ 1+ 2+
4+ 3+ NE 2-3+ 3+ 2-3+ 1+
2+ 4+ 2-3+ 2-3+ 4+
3+ 4+ 3+ 3+ 1+
3+
congestive heart failure, NE
= not
examined.
DiGuglielmo's syndrome
Sepsis >100/3
Early
2-3+ 1-2+
THE THYMUS IN HEMOCHROMATOSIS
Vol. 93, No. 3 December 1978
663
Table 2-Thymic Iron Deposition
Case Overall Endothelial cells Lymphocytes Epithelial cells
Msacrophages Hassall's corpuscles
1
2
3
4
4+
2+ 0 0 2+ 3+ Positive
2+ 0 0 2+ 3+ Positive
3+ 0 0 3+ 3+ Positive
1+
2+ 4+ 4+ None seen
D*ue
The ability of thymic epithelial cells to produce humoral substances has been well established in recent years by the isolation of several components, including thymopoietin and thymosin.4" However, the complex role of the thymus remains a subject of intense investigation, especially with respect to the human organ." The morphologic identification of iron in thymic epithelial cells in our 4 cases of hemochromatosis is of interest in several regards since its presence in the gland warrants explanation. Richter 1 points out that the iron moieties in hemochromatosis, seen microscopically as blue granules in the Gomori's reaction, represent trivalent iron in the form of ferritin or hemosiderin. Intracellular iron moieties arise by pinocytosis by cells as seen in vascular endothelial cells or by synthesis as seen in hepatocytes, proximal renal tubule cells, and cardiac muscle cells. Their presence in thymic lymphoid and epithelial and macrophage cells, however, would dispute the existence of an impenetrable blood-thymus barrier which had been postulated to explain the peculiar anatomic structure of the gland with its epithelial sheathed vasculature and its failure to produce antibodies against circulating antigen.7'8 Since our age-involuted thymic glands represent a predominantly medullary component and showed no demarcation between cortex and medulla, the existence of iron in our cases may be interpreted to support the limited blood-thymus barrier proposed by Raviola and Karnovsky,' in which only the cortex was found to be protected from tracer components. On the other hand, preferential deposition in thymic macrophages, epithelial cells, and Hassall's corpuscles (thought to be epithelial) suggests a more specific metabolic role for these cells. Since the organelles required for ferritin and hemosiderin processing exist in thymic epithelial cells,1F'2 intracellular synthesis of ferritin and hemosiderin may be the main source of iron deposition in this gland. Investigating humoral substances such as thymosin and thymopoietin, previous workers established the presence of rough endoplasmic reticulum, Golgi apparatus, related vacuoles, and lysosomes in thymic epithelial cells: the very organelles required for iron
664
VIGORITA AND HUTCHINS
American Journal of Pathology
processing. The high content of iron in macrophages in our cases presumably reflects their phagocytic activity. In conclusion, the presence of iron moieties in age-involuted thymus glands in cases of secondary or exogenous hemochromatosis recalls the poorly understood preferential deposition of iron elsewhere in the body. It disputes the existence of an impenetrable blood-thymus bamer and further suggests an endocrine or secretory nature of this gland. Referencs 1. Richter GW: The iron-loaded cell-The cytopathology of iron storage. Am J Pathol 91:363-396, 1978 2. Sheldon JH: Haemochromatosis. NMilford, Oxford Medical Publications, London, 1935
3. MacDonald RA: Hemochromatosis and hemosiderosis. Springfield, Ill., Charles C. Thomas, Publisher, 1964 4. Goldstein G: Isolation of bovine thN-min: A polypeptide hormone of the thymus. Nature 247: 11-14, 1974 5. Goldstein AL, Slater FD, White A: Preparation, assay, and partial purification of a thymic lymphocytopoietic factor (thymosin). Proc Natl Acad Sci USA 56:1010-1017. 1966
6. White A: Nature and biological activities of thymus hormones: Prospects for the future. Ann NY Acad Sci 249:23-530, 1973 7. Marshall AHE, White RG: The immunological reactivity of the thymus. Br J Exp Pathol 42:379-385, 1961 8. Clark SL Jr: The thymus in mice of strain 129, J, studied with the electron microscope. Am J Anat 112:1-33, 1963 9. Raviola E, Karnovsky MJ: Evidence for a blood-thymus barrier using electronopaque tracers. J Exp Med 136:466-498, 1972 10. Clark SL Jr: Incorporation of sulfate by the mouse thymus: Its relation to secretion by medullary epithelial cells and to thymic lmphopoiesis. J Exp Med 128:927-958, 1968 11. Abraham R, Morris M, Hendy R: Lysosomal changes in epithelial cells of the mouse thymus after hydrocortisone treatment. Histochemie 17:295-311, 1969 12. Vetters JM, Macadam RF: Fine structural evidence for hormone secretion by the human thymus. J Clin Pathol 26:194-197, 1973
-* PI
*
r
A.,
-Lil
I I
1
2
Fe 1-Overview of a portion of a thymic lobule from Case 1. There is extensive fine particulate iron in the cytoplasm of epithelial cells. No iron can be discerned in lymphoInset-Cytoplasmic granules of iron in epithelial cells. cytes or endothelial cells. Figr 2-Small particles of iron-positive material are (H&E, X400; inset, X1200) found in lymphocytes and endothelial cells in addition to the severe deposition in thymic epithelial cells. A macrophage (arrow) contains a large mass of hemosiderin. (Gomori iron reaction, x 800)
Although iron in cases of hemochromatosis has been described in virtually everv organ, its presence in the thymus has only been rarely observed. While investigating all cases of hemochromatosis autopsied at The Johns Hopkins Hospital over the past decade, 4 adult cases in which the thymus was available for histologic study were examined in light of recent documentation of this organ's role in lymphopoiesis and secretory activity. Iron-containing moieties were found within both lymphocvtes and epithelial cells of these involuted thymic glands. The thvmic iron suggests either an uptake of iron moieties from the vascular pool or their synthesis within the cell itself. While the former mechanism provides evidence against the existence of an impermeable bloodthymus barrier, the latter supports the existence of a metabolicallv active gland with complex function. (Am J Pathol 93:661-666, 1978)
HEMOCHROMATOSIS is a disease of multiple causes in which iron deposition takes place in parenchymal cells throughout the body, which is usually associated with changes such as fibrosis in the liver.' Although its mechanism is not understood, the predilection of iron distribution for organs with exocrine and endocrine function is well known.2'3 The deposition of stainable iron in the anterior lobe of the pituitary, the zona glomerulosa of the adrenals, and the sweat glands of the skin suggests that even within certain organs and tissues there appears to be a preferential pattern. Herein we report 4 cases of iron involvement of ageinvoluted thymic glands in cases of secondary or exogenous hemochromatosis and suggest that the extent of iron observed indicates a predilection for the thymus similar to glandular components elsewhere in the body, perhaps a further indication of the complex secretory nature of the thymus. Materials and Methods All hemochromatosis cases in which autopsies w%-ere performed at The Johns Hopkins Hospital over the past decade were clinically and pathologically reviewed. (Hemochromatosis is defined as the parenchymal distribution of iron with associated tissue changes such as fibrosis or cirrhosis in the liver.') Four cases revealed identifiable, although age-involuted, thymic tissue. All histologic material was reviewed by light microscopy and sections stained by the Gomori iron reaction. Fragments of tissue which had been embedded in paraffin were reprocessed for electron microscopy. The severitx of iron in the From the Department of Pathology of The Johns Hopkins Medical Institutions. Baltimore. Marv and. Supported by Grant HL-14153 from the National Institutes of Health. Accepted for publication Julv 24, 1978. Address reprint requests to Dr. Grover M. Hutchins. Department of Pathology. The Johns Hopkins Hospital, Baltimore, MD 21205. 0002-9440/78/121 1 -0661S01 .00 661 0 1978 American Association of Pathologists
662
American Journal of Pathology
VIGORITA AND HUTCHINS
thymus as well as other tissues was graded on a scale of 0 to 4+, representing no involvement to severe involvement, respectively. Particular attention was given to the thymus to determine what cellular components were involved.
Results
The clinical information is reviewed in Table 1. In all cases there was a history of exogenous hemochromatosis with an underlying chronic anemia requiring multiple blood transfusions which reached massive proportions in 2 cases. Cirrhosis of the liver was present in all cases. The parenchymal distribution of iron was moderate to severe throughout, as tabulated. Although in all cases the thymus was age-involuted precluding a clear demarcation between medullary and cortical regions, iron was found throughout the remaining tissue but was restricted to intracytoplasmic localization (Figures 1 and 2). Whereas epithelial cells and macrophages were involved in all cases, endothelial cells and lymphocytes revealed iron by light microscopy in only Case 1, the most severely affected case (Table 2). Hassall's corpuscles showed positive staining in all but Case 1, in which no corpuscles were seen. Electron microscopy confirmed the intracellular, intracytoplasmic localization of iron. In all cases, iron deposition in epithelial cells and macrophages was more severe than in the other cellular components of the gland. Table 1-Patients Studied Age (yr) Race
1 72 Black
Sex Major clinical diagnosis
Male Refractory anemia
Cause of death Transfusions/years Cirrhosis Tissue iron Liver Pancreas
Case
Spleen Endocrine Thyroid Adrenals Parathyroid
Pituitary Stomach Kidneys Lungs CHF
=
4 70 Black Female
CHF 250 units/3 Severe
2 3 54 49 Black White Male Female Ethanolism Sideroblastic Folate-deficanemia ient megaloblastic anemia CHF Meningitis Few/3 Many/1 0 Early Severe
4+ 4+ 2+
2-3+ 2+ 3-4+
3-4+ 3+ 0-1+
3+ 3+ 3+
4+
2+ 0-1 + 2+ 2-3+ 2+ 1+ 2+
4+ 3+ NE 2-3+ 3+ 2-3+ 1+
2+ 4+ 2-3+ 2-3+ 4+
3+ 4+ 3+ 3+ 1+
3+
congestive heart failure, NE
= not
examined.
DiGuglielmo's syndrome
Sepsis >100/3
Early
2-3+ 1-2+
THE THYMUS IN HEMOCHROMATOSIS
Vol. 93, No. 3 December 1978
663
Table 2-Thymic Iron Deposition
Case Overall Endothelial cells Lymphocytes Epithelial cells
Msacrophages Hassall's corpuscles
1
2
3
4
4+
2+ 0 0 2+ 3+ Positive
2+ 0 0 2+ 3+ Positive
3+ 0 0 3+ 3+ Positive
1+
2+ 4+ 4+ None seen
D*ue
The ability of thymic epithelial cells to produce humoral substances has been well established in recent years by the isolation of several components, including thymopoietin and thymosin.4" However, the complex role of the thymus remains a subject of intense investigation, especially with respect to the human organ." The morphologic identification of iron in thymic epithelial cells in our 4 cases of hemochromatosis is of interest in several regards since its presence in the gland warrants explanation. Richter 1 points out that the iron moieties in hemochromatosis, seen microscopically as blue granules in the Gomori's reaction, represent trivalent iron in the form of ferritin or hemosiderin. Intracellular iron moieties arise by pinocytosis by cells as seen in vascular endothelial cells or by synthesis as seen in hepatocytes, proximal renal tubule cells, and cardiac muscle cells. Their presence in thymic lymphoid and epithelial and macrophage cells, however, would dispute the existence of an impenetrable blood-thymus barrier which had been postulated to explain the peculiar anatomic structure of the gland with its epithelial sheathed vasculature and its failure to produce antibodies against circulating antigen.7'8 Since our age-involuted thymic glands represent a predominantly medullary component and showed no demarcation between cortex and medulla, the existence of iron in our cases may be interpreted to support the limited blood-thymus barrier proposed by Raviola and Karnovsky,' in which only the cortex was found to be protected from tracer components. On the other hand, preferential deposition in thymic macrophages, epithelial cells, and Hassall's corpuscles (thought to be epithelial) suggests a more specific metabolic role for these cells. Since the organelles required for ferritin and hemosiderin processing exist in thymic epithelial cells,1F'2 intracellular synthesis of ferritin and hemosiderin may be the main source of iron deposition in this gland. Investigating humoral substances such as thymosin and thymopoietin, previous workers established the presence of rough endoplasmic reticulum, Golgi apparatus, related vacuoles, and lysosomes in thymic epithelial cells: the very organelles required for iron
664
VIGORITA AND HUTCHINS
American Journal of Pathology
processing. The high content of iron in macrophages in our cases presumably reflects their phagocytic activity. In conclusion, the presence of iron moieties in age-involuted thymus glands in cases of secondary or exogenous hemochromatosis recalls the poorly understood preferential deposition of iron elsewhere in the body. It disputes the existence of an impenetrable blood-thymus bamer and further suggests an endocrine or secretory nature of this gland. Referencs 1. Richter GW: The iron-loaded cell-The cytopathology of iron storage. Am J Pathol 91:363-396, 1978 2. Sheldon JH: Haemochromatosis. NMilford, Oxford Medical Publications, London, 1935
3. MacDonald RA: Hemochromatosis and hemosiderosis. Springfield, Ill., Charles C. Thomas, Publisher, 1964 4. Goldstein G: Isolation of bovine thN-min: A polypeptide hormone of the thymus. Nature 247: 11-14, 1974 5. Goldstein AL, Slater FD, White A: Preparation, assay, and partial purification of a thymic lymphocytopoietic factor (thymosin). Proc Natl Acad Sci USA 56:1010-1017. 1966
6. White A: Nature and biological activities of thymus hormones: Prospects for the future. Ann NY Acad Sci 249:23-530, 1973 7. Marshall AHE, White RG: The immunological reactivity of the thymus. Br J Exp Pathol 42:379-385, 1961 8. Clark SL Jr: The thymus in mice of strain 129, J, studied with the electron microscope. Am J Anat 112:1-33, 1963 9. Raviola E, Karnovsky MJ: Evidence for a blood-thymus barrier using electronopaque tracers. J Exp Med 136:466-498, 1972 10. Clark SL Jr: Incorporation of sulfate by the mouse thymus: Its relation to secretion by medullary epithelial cells and to thymic lmphopoiesis. J Exp Med 128:927-958, 1968 11. Abraham R, Morris M, Hendy R: Lysosomal changes in epithelial cells of the mouse thymus after hydrocortisone treatment. Histochemie 17:295-311, 1969 12. Vetters JM, Macadam RF: Fine structural evidence for hormone secretion by the human thymus. J Clin Pathol 26:194-197, 1973
-* PI
*
r
A.,
-Lil
I I
1
2
Fe 1-Overview of a portion of a thymic lobule from Case 1. There is extensive fine particulate iron in the cytoplasm of epithelial cells. No iron can be discerned in lymphoInset-Cytoplasmic granules of iron in epithelial cells. cytes or endothelial cells. Figr 2-Small particles of iron-positive material are (H&E, X400; inset, X1200) found in lymphocytes and endothelial cells in addition to the severe deposition in thymic epithelial cells. A macrophage (arrow) contains a large mass of hemosiderin. (Gomori iron reaction, x 800)
