HMB45 protein expression and the immunohistochemical maturation in common blue nevi: a reappraisal

ommon blue nevi, first described by Jadassohn-Tièche n 1906, are melanocytic proliferations composed of igmented cells reminiscent of the embryonal neural cresterived dendritic melanocytic precursors. They commonly ccur on the dorsal aspects of extremities, scalp, and butocks of children and young adults. Histologically, blue nevi re composed of a symmetrical circumscribed dermal proiferation of pigmented dermal spindle-shaped dendritic elanocytes that have a propensity to extend about the cells (cytoplasmic staining) was evaluated in 100 cells in 4 high-power fields and reported as the percentage of positive cells following other groups.8 The data were analyzed using SPSS (version 17, IL, Chicago). The patients with blue nevi included 11 females and nine males. Their mean age was 53.3 ± 4.1 years (age range: 7--88 years). The locations with the highest frequencies of blue nevi were the head and neck (nose, forehead, and scalp: 9 cases), extremities (shoulder region and arm:7 cases), and back (2 cases) and chest (2 cases). Most of the cases were pigmented with a clinical appearance similar to seborrheic keratosis or atypical nevi. All common blue and intradermal benign nevi showed strong and diffuse S100 and Melan-A staining throughout the entire lesions. No appreciable KI67 staining was seen in blue or intradermal nevi (Ki67 labeling index was 0--1%). All cases of intradermal nevi lacked the expression of HMB45 protein. In contrast, all blue nevi expressed HMB45 protein. Three expression patterns were observed: diffuse, patchy, or occasional HMB45 positive cells (Figs. 1--2). The percentage of positive cells ranged from 5% to 85% (mean value: 49.2 ± 6.4). There was no correlation between the HMB45 expression values and clinical features (age and gender of the patient, or site, size of the lesions). Several studies indicated that HMB-45 staining could highlight the pattern of ‘‘immunohistochemical maturation’’ of the melanocytic lesions. The activated junctional or superficial, type A melanocytes (epithelioid cells) express HMB45, while the deeply located type C melanocytes (spindle cells) do not express this antibody.3,5 In agreement with the previous investigations,6 all common blue nevi in this study showed a variable expression of HMB45 proteins. Wood et al. immunohistochemically examined HMB45 protein expression in blue nevi. They found diffuse strong HMB45 reactivity in all cellular blue nevi and variable HMB45 protein expression in most of the common blue nevi. The authors suggested that blue nevi have an activated phenotype. Similarly, Sun et al reported the expression of HMB45 protein in 16 cases of blue nevi. The authors suggested that the nevic cells of blue nevi cells are derived from a precursor cell that has some common features of both melanocyte and Schwann cells.7 In this study, the preserved HMB45 protein expression in both superficial and deep portions of the lesions implies the lack of immunohistochemical maturation in blue nevi. This preserved HMB45 protein expression in these nevic cells is indicative of their activated phenotype with active melanosome formation. Although mechanisms underlying this activated phenotype in common blue nevi are unknown, it may be reasoned to the release of melanocytic growth factors such as hepatocyte growth factor, endothelin-1, and -melanocyte-stimulating hormone. These factors can alter the HMB45 protein glycosylation during various pathogenic states of melanocytes, help activate melanogenesis, and s r dnexal structures or neurovascular bundles. These denritic cells are admixed with variable numbers of oval elanocytes reminiscent of intermediate (type B) and pindly neurotized (type C) nevic cells. Common blue nevi rise following the proliferation of the residual dermal denritic melanocytic pool originating from the neural crest, ossibly initiated by dermal inflammation or other stimuli. hese nevi may arise from mutated precursor stem cells in he dermis, capable of differentiating into blue nevi.1,2 The human homolog of the mouse silver protein (gp100 or mel17) is a melanocytes specific type I membrane protein. t is important for the formation of melanosomal fibrils that elp the maturation of stage I pre-melanosomes to stage I. The HMB45 antibody was developed from an extract of lymph-node metastasis of melanoma. It specifically reacts ith the glycosylated form of gp100 restricted to the fibrillar atrix of stage II pre-melanosomes.3 The gene correspondng to the HMB45 defined protein has recently been cloned nd designated gp 100-cl. HMB-45 binds to stage 1 and 2 elanosomes and to the non-melanized portion of stage , whereas stage 4 melanosomes and melanosome comlexes found in macrophages and keratinocytes have been egative.3--5 HMB-45 immunoreactivity is frequently noted in etal and neonatal melanocytes (oncofetal protein) but not n adult resting melanocytes. HMB45 is re-expressed in most alignant melanomas, in the activated melanocytes such s some junctional nevic cells, atypical nevi, traumatized evus, and melanocytes of blue nevi.3,5 To date, knowledge about the expression patterns of MB45 protein in common blue nevi is limited.6,7 The purose of this study was to examine the maturation of the ermal melanocytes, using HMB45 protein expression, in series of common blue nevi. To accomplish this goal, he formalin-fixed, paraffin-embedded specimens of comon blue nevi (20 cases) and intradermal nevi (20 cases) ere retrieved from the archives of the Pathology Departent, and the consultation files of this author, at Assuit niversity Hospitals. The immunohistological sections were eviewed for the expression of the melanocytic (S100: clone C4.9, Melan A: clone: A103, HMB45: clone HMB45 monclonal antibodies) and proliferation markers (Ki67: clone 0-9 polyclonal antibody). The number of HMB45 positive


Dear Editor,
Common blue nevi, first described by Jadassohn-Tièche in 1906, are melanocytic proliferations composed of pigmented cells reminiscent of the embryonal neural crestderived dendritic melanocytic precursors. They commonly occur on the dorsal aspects of extremities, scalp, and buttocks of children and young adults. Histologically, blue nevi are composed of a symmetrical circumscribed dermal proliferation of pigmented dermal spindle-shaped dendritic melanocytes that have a propensity to extend about the adnexal structures or neurovascular bundles. These dendritic cells are admixed with variable numbers of oval melanocytes reminiscent of intermediate (type B) and spindly neurotized (type C) nevic cells. Common blue nevi arise following the proliferation of the residual dermal dendritic melanocytic pool originating from the neural crest, possibly initiated by dermal inflammation or other stimuli. These nevi may arise from mutated precursor stem cells in the dermis, capable of differentiating into blue nevi. 1,2 The human homolog of the mouse silver protein (gp100 or Pmel17) is a melanocytes specific type I membrane protein.
It is important for the formation of melanosomal fibrils that help the maturation of stage I pre-melanosomes to stage II. The HMB45 antibody was developed from an extract of a lymph-node metastasis of melanoma. It specifically reacts with the glycosylated form of gp100 restricted to the fibrillar matrix of stage II pre-melanosomes. 3 The gene corresponding to the HMB45 defined protein has recently been cloned and designated gp 100-cl. HMB-45 binds to stage 1 and 2 melanosomes and to the non-melanized portion of stage 3, whereas stage 4 melanosomes and melanosome complexes found in macrophages and keratinocytes have been negative. 3---5 HMB-45 immunoreactivity is frequently noted in fetal and neonatal melanocytes (oncofetal protein) but not in adult resting melanocytes. HMB45 is re-expressed in most malignant melanomas, in the activated melanocytes such as some junctional nevic cells, atypical nevi, traumatized nevus, and melanocytes of blue nevi. 3,5 To date, knowledge about the expression patterns of HMB45 protein in common blue nevi is limited. 6,7 The purpose of this study was to examine the maturation of the dermal melanocytes, using HMB45 protein expression, in a series of common blue nevi. To accomplish this goal, the formalin-fixed, paraffin-embedded specimens of common blue nevi (20 cases) and intradermal nevi (20 cases) were retrieved from the archives of the Pathology Department, and the consultation files of this author, at Assuit University Hospitals. The immunohistological sections were reviewed for the expression of the melanocytic (S100: clone 4C4.9, Melan A: clone: A103, HMB45: clone HMB45 monoclonal antibodies) and proliferation markers (Ki67: clone 30-9 polyclonal antibody). The number of HMB45 positive ଝ Study conducted at the Department of Pathology, Faculty of Medicine, Assiut University Hospitals, Egypt. cells (cytoplasmic staining) was evaluated in 100 cells in 4 high-power fields and reported as the percentage of positive cells following other groups. 8 The data were analyzed using SPSS (version 17, IL, Chicago).
The patients with blue nevi included 11 females and nine males. Their mean age was 53.3 ± 4.1 years (age range: 7---88 years). The locations with the highest frequencies of blue nevi were the head and neck (nose, forehead, and scalp: 9 cases), extremities (shoulder region and arm:7 cases), and back (2 cases) and chest (2 cases). Most of the cases were pigmented with a clinical appearance similar to seborrheic keratosis or atypical nevi. All common blue and intradermal benign nevi showed strong and diffuse S100 and Melan-A staining throughout the entire lesions. No appreciable KI67 staining was seen in blue or intradermal nevi (Ki67 labeling index was 0---1%). All cases of intradermal nevi lacked the expression of HMB45 protein. In contrast, all blue nevi expressed HMB45 protein. Three expression patterns were observed: diffuse, patchy, or occasional HMB45 positive cells (Figs. 1---2). The percentage of positive cells ranged from 5% to 85% (mean value: 49.2 ± 6.4). There was no correlation between the HMB45 expression values and clinical features (age and gender of the patient, or site, size of the lesions).
Several studies indicated that HMB-45 staining could highlight the pattern of ''immunohistochemical maturation'' of the melanocytic lesions. The activated junctional or superficial, type A melanocytes (epithelioid cells) express HMB45, while the deeply located type C melanocytes (spindle cells) do not express this antibody. 3,5 In agreement with the previous investigations, 6 all common blue nevi in this study showed a variable expression of HMB45 proteins. Wood et al. immunohistochemically examined HMB45 protein expression in blue nevi. They found diffuse strong HMB45 reactivity in all cellular blue nevi and variable HMB45 protein expression in most of the common blue nevi. The authors suggested that blue nevi have an activated phenotype. Similarly, Sun et al reported the expression of HMB45 protein in 16 cases of blue nevi. The authors suggested that the nevic cells of blue nevi cells are derived from a precursor cell that has some common features of both melanocyte and Schwann cells. 7 In this study, the preserved HMB45 protein expression in both superficial and deep portions of the lesions implies the lack of immunohistochemical maturation in blue nevi. This preserved HMB45 protein expression in these nevic cells is indicative of their activated phenotype with active melanosome formation. Although mechanisms underlying this activated phenotype in common blue nevi are unknown, it may be reasoned to the release of melanocytic growth factors such as hepatocyte growth factor, endothelin-1, and ␣-melanocyte-stimulating hormone. These factors can alter the HMB45 protein glycosylation during various pathogenic states of melanocytes, help activate melanogenesis, and stimulate the motility and proliferation of the normal resting residual cells at the dermal melanocyte pools. 9 It is possible that the cells of the common blue nevi directly arise from the activated extrafollicular dermal melanocyte stem cells. The latter persist after birth in the superficial nerve sheath of peripheral nerves. These cells can proliferate, giving rise to migratory melanocyte precursors with activated phenotype and HMB45 protein expression. 10 To conclude,

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Authors' contributions
Mahmoud Rezk Abbelwahed Hussein fully and solely contributed to the followings: Approval of the final version of the manuscript; critical literature review; data collection, analysis, and interpretation; effective participation in research orientation; intellectual participation in propaedeutic and/or therapeutic; management of studied cases; manuscript critical review; preparation and writing of the manuscript; statistical analysis; and study conception and planning.