MAST CELLS AND APOPTOTIC BODIES IN SEBORRHEIC KERATOSIS: A COMPARATIVE STUDY BETWEEN UVB INDUCED SEBORRHEIC KERATOSIS IN MICE AND SPORADIC CASES IN HUMANS

Abstract

Background Exposure to ultraviolet type B (UVB) radiation induces a number of pathologic changes in skin, including erythema, edema, epidermal hyperplasia, sunburn cell formation, immune suppression and eventually leads to cancer development. Objective To elucidate the differences in histological appearances of mast cells and apoptotic bodies between the two species (mice and human) among hyperkeratotic and acanthotic types of seborrheic keratosis (SK). Materials and methods Thirty paraffin blocks were used in this study; fifteen histologically confirmed acanthotic and hyperkeratotic SK cases in human (9 acanthotic and 6 hyperkeratotic) and fifteen blocks from both types acanthotic and hyperkeratotic SK cases in mice induced by UVB light (9 acanthotic and 6 hyperkeratotic). Results Our results revealed that there was a significant correlation between mast cells and apoptotic bodies for both groups according to Pearson Correlation test. In human cases mast cells counting ranged between 2-10 with a mean number of 5.2/1HPF, while the total number of apoptotic bodies ranged from 1-4 with a mean number of 2.6/10HPF. When compared to mice cases, the number of mast cells were increased with a range of 12-23 and with a mean number of 19.067/1HPF, while apoptotic bodies were decreased with a range of 3-20/10HPF and with a mean number of 9.4/10HPF. Conclusion Dermal mast cells infiltration were remarkably increased in mice skin specimens which were exposed to UVB. The number of apoptotic bodies in UVB induced cases were more than in human sporadic cases. Keyword: UVB, seborrheic keratosis, apoptotic bodies, mast cells. * Department of Pathology and Forensic Pathology, School of Medicine, Sulaimani University. Correspondence : iraqnabil1954@gmail.com **Department of Histopathology, College of Veterinary Medicine, Sulaimani University. Salmo N A M et al. / JSMC, 2014 (Vol 4) No.2 116 jsmc INTRODUCTION The skin is the primary barrier against the external environment. The epidermal cells are the first cells to be exposed to physical and chemical genotoxic agents such as ultraviolet (UV) and ionizing radiations (IR) (1). UVB radiation induces a number of pathologic changes in skin, including erythema, edema, epidermal hyperplasia, sunburn cell formation, immune suppression and changes in expression of numerous genes associated with proliferation, differentiation and skin cancer (2-3). SK are the commonest benign epithelial tumors in older people; their prevalence increases with age (4). SK are detected in 80-100% of people over 50 years and are typically localized on the head, the trunk and the extremities with the exception of the palms and soles. SK develop from the proliferation of epidermal cells (5-6). The etiology of SK is still controversial, numerous studies regarded as of unknown etiology (7,8), not related to sun exposure (9-14), viral etiology (7, 15), or due to a mutation of a gene coding for a fibroblast growth factor receptor (FGFR3) (5,16). However two previous studies induced SK in mice by UVB exposure (2,17). One of the hallmark events of exposing skin to UVB radiation is the formation of sunburn cells (SC) (18), which are crucial protective mechanisms against the carcinogenic effects of UVB irradiation (19). The formation of sunburn cells in UV-exposed skin indicates the severity of DNA damage. The repair of DNA damage in UVB exposed skin cells can prevent further damage. If they are not repaired, they may continue to replicate and may lead to cutaneous malignancies (20). UV is also immunosuppressive and numerous studies have shown that UV-induced immune suppression is a major risk factor for skin cancer induction (21). The exact process by which mast cells contribute to immune suppression is not known. Mast cells have been found to play a critical role in the suppression of immune reactions and not only through production of inhibitory cytokine interleukin 10 (IL-10). Thus, mast cell infiltration into tumor may possibly remodel tumor microenvironment and profoundly influence tumor behavior by participating and regulating inflammatory and immune reactions (22). The present study was designed to elucidate the differences in histological appearance of mast cells and apoptotic bodies between the two species (mouse and human) among different types of SK. MATERIALS AND METHODS