Is Herpes Simplex Virus (HSV) infection a risk factor for nasopharyngeal carcinoma?

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Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), are two members of the herpesvirus family, that infect humans (Ryan and Ray, 2004).HSV-1 and HSV-2 have developed several mechanisms to escape host detection and immune responses and usually establish lifelong latency (Kenneth, et al. 2014) HSV-1 has been identified in benign and malignant thyroid tumours, whereas HSV-2 has been found to be associated with papillary thyroid cancer and the presence of lymph node metastases (Jensen, et al. 2010) Moreover, HSV-2 is associated with prostate cancer, melanoma incidence in both men and women (Thomas, et al. 2011), and cervical cancer (Haverkos, et al. 2000).
Although the probability of an association between HSV and cancer has been proposed [12,13], but so far it has not been likely to demonstrate that HSV can make primary transformation of normal cells in to malignant.Inoculation of HSV-1 and HSV2 into hamsters rarely leads to the induction of a tumor, and it has been difficult to demonstrate herpes viral antigens in a tumor cells (Duff and Rapp, 1971).However, there is a complete lack of literature regarding the relationship between NPC and HSV, therefore, the aim of this study was to screen for the presence of HSV amongst Sudanese patients with PC.

MATERIALS AND METHODS
In this study 150 formalin fixed paraffin wax processed tissue samples of nasopharyngeal carcinoma were obtained from earlier operated patients from different histopathology laboratories in Khartoum State, Sudan.All tissue samples were from those who had not yet given anti-cancer therapy.The study was approved by the Ethical Committee of the Research Board of Faculty of Medical Laboratory Science, Sudan University for Science and Technology, Khartoum, Sudan.
DNA Extraction: DNA was extracted from paraffin-embedded samples, by immersing tissue section in xylene to dissolve the paraffin from the tissue, and then rehydrated using a series of ethanol washes.Proteins and harmful enzymes such as nucleases were digested by proteinase K. Buffer containing denaturing agent (sodium dodecyl sulfate (SDS)), was added to facilitate digestion (Hilz, et al .1975).Nucleic acids were purified from the tissue lysate using buffer-saturated phenol and high speed centrifugation.Following phenol extractions, RNase A was added to eliminate contaminating RNA.Additional phenol extractions following incubation with RNase A were used to remove any remaining enzyme.Sodium acetate and isopropanol were added to precipitate DNA, and high speed centrifugation was used to pellet the DNA and facilitate isopropanol removal.Washing with 70% ethanol was performed to remove excess salts, followed by centrifugation to re-pellet the DNA (Joseph, 2001;Pikor, et al. 2011).DNA is resuspended in distilled water, quantified and stored at -20°C Purified DNA was subsequently used in downstream applications of PCR.

DISCUSSION
In the present study we attempted to investigate the relationship between HSV and NPC, though there is an extreme lack of literature in this context.Herpes simplex virus type 1 (HSV-1) is a widespread human pathogen infecting more than 80% of the population worldwide.Its replication involves an essential, poorly understood multistep process, referred to as uncoating (Liashkovich, et al. 2011).
However, HSV impair the immune system by disturbing T-cell receptor signalling.These viruses inhibit the T-cell receptor (TCR)-stimulated formation of a linker required for the activation of a T-cell signalling complex.As a consequence, TCRstimulated NF-κB activation and selective TCR-stimulated interleukin-10 synthesis are inhibited, which in turn favoured viral replication and blocked cellular immunity (Sloan, et al. 2007).HSV was found to inhibit the type I interferon response (Murphy, et al. 2003), and HSV-1 infected cells can resist T-cell induced apoptosis through expression of the Us5 gene product gJ (Jerome, et al. 2001).The relationship between HSV immune disturbance and cancer can be expressed by the hypothesis of tumour immunosurveillance.It was stated that the human body employs its natural defences and exhibits immunological resistance to the development of cancer.This immunological response happens during the early stages of cancer growth.The clinically noticeable signs of tumour disease can only be seen after the cancerous cells have already escaped the immune response (Peto, 2001).
However, although the percentage of infection with HSV is relatively low among NPC, but most of these cases have a coinfection with EBV prime suspect risk factor for NPC.In vitro and animal models suggest that the HSV-1 may play a role in the development of oropharyngeal squamous cell carcinoma (OSCC) (Jacqueline, et al. 2000).The persistence of the HSV in the oral cavity and its capability to stimulate host DNA synthesis and repair during reactivations proposes that it may contribute to OSCC development.In fact, in vitro studies have clarified specific mechanisms over which HSV1 may induce the transformation of human cells: HSV1 infection of human cell cultures has been revealed to be mutagenic (Das, et al. 1998), and inhibit apoptosis (Jerome, et al. 1998), which may contribute to carcinogenesis (Polverini and Nor, 1999).Some studies found that HSV1 was particularly associated with OSCC risk when other risk factors, such as cigarette smoking or a history of HPV infection, are present (Jacqueline, et al. 2000).Furthermore, the significant presence of co-infection between HSV and EBV, may have synergistic effects in the development of NPC.
Regarding age most of HSV infections were observed among elder patients.Also regarding residence, most infections were seen among those patients coming from South.
In conclusion: The present have shown some weak links between HSV and NPC.The great majority of samples harboring HSV were also found to harbor EBV, which suggests the potentiality of EBV over HSV.

Fig. 1 :
Fig. 1: Description of the study population by sex and HSV-2.

Fig. 2 :
Fig. 2: Description of the study subjects by age

Fig. 3 :
Fig. 3: Description of study population by residence and HSV-2 infection

Table 1 :
Distribution of the study population by residence and HSV-2 infection