The cellular Notch1 protein promotes KSHV reactivation in an Rta-dependent manner.

The cellular Notch signal transduction pathway is intimately associated with infections by Kaposi's sarcoma-associated herpesvirus (KSHV) and other gamma-herpesviruses. RBP-Jk, the cellular DNA binding component of the canonical Notch pathway, is the key Notch downstream effector protein in virus-infected and uninfected animal cells. Reactivation of KSHV from latency requires the viral lytic switch protein, Rta, to form complexes with RBP-Jk on numerous sites within the viral DNA. Constitutive Notch activity is essential for KSHV pathophysiology in models of Kaposi's sarcoma (KS) and Primary Effusion Lymphoma (PEL), and we demonstrate that Notch1 is also constitutively active in infected Vero cells. Although the KSHV genome contains >100 RBP-Jk DNA motifs, we show that none of the four isoforms of activated Notch can productively reactivate the virus from latency in a highly quantitative trans-complementing reporter virus system. Nevertheless, Notch contributed positively to reactivation because broad inhibition of Notch1-4 with gamma-secretase inhibitor (GSI) or expression of dominant negative mastermind-like1 (dnMAML1) coactivators severely reduced production of infectious KSHV from Vero cells. Reduction of KSHV production is associated with gene-specific reduction of viral transcription in both Vero and PEL cells. Specific inhibition of Notch1 by siRNA partially reduces the production of infectious KSHV, and NICD1 forms promoter-specific complexes with viral DNA during reactivation. We conclude that constitutive Notch activity is required for the robust production of infectious KSHV, and our results implicate activated Notch1 as a pro-viral member of a MAML1/RBP-Jk/DNA complex during viral reactivation. IMPORTANCE: Kaposi's sarcoma-associated herpesvirus (KSHV) manipulates the host cell oncogenic Notch signaling pathway for viral reactivation from latency and cell pathogenesis. KSHV reactivation requires that the viral protein Rta functionally interacts with RBP-Jk, the DNA-binding component of the Notch pathway, and with promoter DNA to drive transcription of productive cycle genes. We show that the Notch pathway is constitutively active during KSHV reactivation and is essential for robust production of infectious virus progeny. Inhibiting Notch during reactivation reduces the expression of specific viral genes yet does not affect the growth of the host cells. Although Notch cannot reactivate KSHV alone, the requisite expression of Rta reveals a previously unappreciated role for Notch in reactivation. We propose that activated Notch cooperates with Rta in a promoter-specific manner that is partially programmed by Rta's ability to redistribute RBP-Jk DNA binding to the virus during reactivation.

Primary Classic Penile Kaposi's Sarcoma in a Middle Age Circumcised HIV-Negative Patient: Presentation of an Unusual Case.

Kaposi's sarcoma should be considered in the differential diagnosis in young patients with penile lesions and no risk factors. A 37-year-old heterosexual man with no other medical history applied presented with a non-itchy and painless penile lesion, for three months. The HIV 1-2 serology was negative via ELISA test. Histopathological analysis of the lesion revealed a tumor composed of atypical spindle cells, below a partially ulcerated surface. There was also an abundance of plasma cells admixed within the neoplastic cells. The patient was diagnosed as HIV-negative, HHV-8 positive Kaposi sarcoma. Although penile Kaposi sarcoma is extremely rare, classical Kaposi sarcoma should be considered in the differential diagnosis of penile lesions.

Molecular detection and genotyping of human herpes virus 8 in blood donors in Congo.

OBJECTIVES: Human herpesvirus 8 (HHV8) is rarely studied in Congo, despite its prevalence in Africa. Among healthy individuals, HHV-8 does not always lead to a life-threatening infection; however, in immunocompromised individuals, it could lead to more severe disease. The distribution of HHV-8 genotypes varies depending on ethnicity and geographic region. METHOD: A prospective cross-sectional study included 265 samples from healthy blood donors from the National Blood Transfusion Center in Brazzaville, with an average age of 35 years, with extremes ranging from 18 to 60 years. After DNA extraction, a nested PCR was carried out for molecular detection, followed by genotyping by amplification of specific primers. RESULT: In this study, 4.9% were positive for molecular detection of HHV-8 DNA. All HHV-8 positive DNA samples that were subjected to genotyping by amplification with specific primers allowing discrimination of two major genotypes (A and B). Genotype A was identified in 5 (1.9%) samples and genotype B in 2 (0.7%) samples, indicating that both genotypes were predominant. The remaining viral DNA samples not identified as the major genotypes were classified as «indeterminate¼ and consisted of 6 (2.3%) samples. CONCLUSION: The results of the study suggest that Congo is an area where HHV-8 infection is endemic.

HHV-8 Linked to Kaposi's Sarcoma and Castleman's Disease in HIV-1-infected patient: Case Report and Review of the Literature.

Kaposi's sarcoma (KS) and multicentric Castleman's disease (MCD) are both linked to human herpesvirus-8 (HHV-8) infection which most commonly affects people living with human immunodeficiency virus (HIV).  Herein, we describe the case of a 57-year-old patient who has been admitted for fever, night sweats, weight loss, and diffuse lymphadenopathy with abdominal pain. HIV status was confirmed by a positive Western blot test. His initial CD4 cell count was equal to 270 cells/µL. A histological study of a peripheral lymph node concluded that KS is associated with MCD. These two conditions found in the same patient highlight the malignant potential of HHV-8, particularly in the case of HIV-induced immunodeficiency.

Extracavitary primary effusion lymphoma presenting as a solitary brain mass.

Primary effusion lymphoma (PEL) is an uncommon B-cell lymphoma associated with human herpesvirus 8 and comprises 3-4% of all HIV-related lymphomas. It traditionally presents as a pleural, pericardial, and/or peritoneal effusion, though it can occasionally manifest as an extracavitary or solid mass in the absence of an effusion. The extracavitary or solid variant of primary effusion lymphoma has been reported in the skin, gastrointestinal tract, lung, and lymph nodes. However, very few cases have been reported in the central nervous system. We describe a case of extracavitary or solid variant of primary effusion lymphoma presenting as a brain mass in an HIV-positive man, highlighting the clinicopathologic and immunophenotypic findings of a rare entity.

Primary effusion lymphoma (PEL) is an uncommon and aggressive form of large B-cell lymphoma with a grim outlook, making up less than 1% of all lymphomas. PEL is linked to human herpesvirus 8 and predominantly impacts individuals with HIV or weakened immune systems. The typical presentation of PEL involves cancerous fluid accumulating in the chest or abdominal cavities. Occasionally, PEL can appear as a solid mass outside these cavities, termed extracavitary PEL (EC-PEL). The case we are describing highlights the difficulties in diagnosing PEL/EC-PEL. It is crucial for healthcare providers to consider EC-PEL when dealing with human herpesvirus 8-positive B-cell lymphomas, especially when patients have weakened immune systems and an unusual clinical scenario involving a solid mass, as seen in this case.

Evaluation of two commercial diagnostic methods for HHV-8 viral load assessment.

Objectives: Human herpesvirus-8 (HHV-8) can cause Kaposi's sarcoma or B lymphoproliferative disorders such as multicentric Castleman disease. Patient follow-up is based on assessing the HHV-8 viral load, which is usually achieved using real-time polymerase chain reaction (PCR). The HHV-8 Premix r-gene kit (BioMérieux) was used by some laboratories in the past, but BioMérieux ceased the production and distribution of this kit in 2021-2022. Other kits need to be tested so that they can be used for diagnostic purposes. Here we evaluated two commercial kits: HHV8 ELITe MGB Kit (ELITech) and Quanty HHV-8 (Clonit) and compared them with the HHV-8 Premix r-gene kit. Methods: We used whole blood samples that had previously been tested with the HHV-8 Premix r-gene kit for diagnostic purposes. Overall, 46 samples (37 HHV-8-positive and 9 HHV-8-negative) were tested with the ELITe MGB Kit and 37 (29 HHV-8-positive and 8 HHV-8-negative) with the Quanty HHV-8 kit. The different methods were compared using Bland-Altman and Passing-Bablok tests with Analyse-it software. Results: Qualitative results were concordant except for one HHV-8 low-positive sample that was found to be negative by the ELITe MGB Kit. The quantitative results were also concordant; both kits showed mean differences of 0.58 log10 copies/ml and 0.73 log10 copies/ml, respectively, compared to the Premix r-gene kit. Conclusions: Both the methods tested produced acceptable results and could be used for diagnostic purposes. It should be remembered that there is no international standard for HHV-8 quantification and that patients should always be followed using the same method.

Pulmonary Kaposi sarcoma in a patient with bilateral lung transplant: An unexpected diagnosis on transbronchial fine needle aspiration and core biopsy.

Kaposi sarcoma (KS) is a low-grade vascular neoplasm that can be seen in various sites, most commonly seen in skin and mucosal tissues. Cytologic features of KS have been well-documented in the literature, however, since it is rarely seen in visceral organs, it could pose significant diagnostic challenges on fine needle aspiration (FNA) biopsies. We present a case of pulmonary KS diagnosed on transbronchial FNA biopsy in a 70-year-old female bilateral lung allograft recipient 11 months after transplantation. The aspirate smears showed a moderately cellular specimen containing a mixture of small, tightly cohesive clusters and loosely clustered groups of monomorphic, ovoid to spindled cells with moderate nuclear to cytoplasmic ratio. An extensive immunohistochemical panel on the concurrent core biopsy showed the tumor cells to be positive for ERG, KIT, and HHV8, confirming the diagnosis. We compared our case to previously published reports of confirmed pulmonary KS in lung allograft recipients.

An Overview of the Unfolded Protein Response (UPR) and Autophagy Pathways in Human Viral Oncogenesis.

Autophagy and Unfolded Protein Response (UPR) can be regarded as the safe keepers of cells exposed to intense stress. Autophagy maintains cellular homeostasis, ensuring the removal of foreign particles and misfolded macromolecules from the cytoplasm and facilitating the return of the building blocks into the system. On the other hand, UPR serves as a shock response to prolonged stress, especially Endoplasmic Reticulum Stress (ERS), which also includes the accumulation of misfolded proteins in the ER. Since one of the many effects of viral infection on the host cell machinery is the hijacking of the host translational system, which leaves in its wake a plethora of misfolded proteins in the ER, it is perhaps not surprising that UPR and autophagy are common occurrences in infected cells, tissues, and patient samples. In this book chapter, we try to emphasize how UPR, and autophagy are significant in infections caused by six major oncolytic viruses-Epstein-Barr (EBV), Human Papilloma Virus (HPV), Human Immunodeficiency Virus (HIV), Human Herpesvirus-8 (HHV-8), Human T-cell Lymphotropic Virus (HTLV-1), and Hepatitis B Virus (HBV). Here, we document how whole-virus infection or overexpression of individual viral proteins in vitro and in vivo models can regulate the different branches of UPR and the various stages of macro autophagy. As is true with other viral infections, the relationship is complicated because the same virus (or the viral protein) exerts different effects on UPR and Autophagy. The nature of this response is determined by the cell types, or in some cases, the presence of diverse extracellular stimuli. The vice versa is equally valid, i.e., UPR and autophagy exhibit both anti-tumor and pro-tumor properties based on the cell type and other factors like concentrations of different metabolites. Thus, we have tried to coherently summarize the existing knowledge, the crux of which can hopefully be harnessed to design vaccines and therapies targeted at viral carcinogenesis.

KSHV genome harbors both constitutive and lytically induced enhancers.

Kaposi's sarcoma-associated herpesvirus (KSHV) belongs to the gamma-herpesvirus family and is a well-known human oncogenic virus. In infected cells, the viral genome of 165 kbp is circular DNA wrapped in chromatin. The tight control of gene expression is critical for latency, the transition into the lytic phase, and the development of viral-associated malignancies. Distal cis-regulatory elements, such as enhancers and silencers, can regulate gene expression in a position- and orientation-independent manner. Open chromatin is another characteristic feature of enhancers. To systematically search for enhancers, we cloned all the open chromatin regions in the KSHV genome downstream of the luciferase gene and tested their enhancer activity in infected and uninfected cells. A silencer was detected upstream of the latency-associated nuclear antigen promoter. Two constitutive enhancers were identified in the K12p-OriLyt-R and ORF29 Intron regions, where ORF29 Intron is a tissue-specific enhancer. The following promoters: OriLyt-L, PANp, ALTp, and the terminal repeats (TRs) acted as lytically induced enhancers. The expression of the replication and transcription activator (RTA), the master regulator of the lytic cycle, was sufficient to induce the activity of lytic enhancers in uninfected cells. We propose that the TRs that span about 24 kbp region serve as a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The silencer and enhancers described here provide an additional layer to the complex gene regulation of herpesviruses.IMPORTANCEIn this study, we performed a systematic functional assay to identify cis-regulatory elements within the genome of the oncogenic herpesvirus, Kaposi's sarcoma-associated herpesvirus (KSHV). Similar to other herpesviruses, KSHV presents both latent and lytic phases. Therefore, our assays were performed in uninfected cells, during latent infection, and under lytic conditions. We identified two constitutive enhancers, one of which seems to be a tissue-specific enhancer. In addition, four lytically induced enhancers, which are all responsive to the replication and transcription activator (RTA), were identified. Furthermore, a silencer was identified between the major latency promoter and the lytic gene locus. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The terminal repeats, spanning a region of about 24 kbp, seem like a "viral super-enhancer" that integrates the repressive effect of the latency-associated nuclear antigen (LANA) with the activating effect of RTA to regulate latency to lytic transition.

Monomorphic T-cell post-transplant lymphoproliferative disorder with features of HHV8-negative primary effusion lymphoma: an autopsy case and review of the literature.

A 67-year-old man underwent renal transplantation in his twenties. He developed refractory pleural effusion, with many large lymphocytes with severe atypia and mitosis in the effusion, indicating malignant lymphoma. He finally died of respiratory failure. An autopsy revealed atypical lymphocytes positive for CD3, CD4, and CD30 and negative for CD8, CD20, PAX5, human herpesvirus (HHV) 8, and Epstein-Barr virus-encoded small RNAs by immunohistochemistry and in situ hybridization. Atypical lymphocytes also had T-cell receptor gene rearrangements Jß2, Jγ2, and Jδ1 and chromosomal aberrations der(8)t(1;8)(q21;p21), add(13)(q12), add(14)(q32), and add(16)(q12-13). A few atypical lymphocytes were present at other sites. We finally diagnosed this case as monomorphic T-cell post-transplant lymphoproliferative disorder with features of HHV8-negative primary effusion lymphoma. A literature review only identified six cases (four HHV8-negative, two HHV8-positive) of effusion lymphoma of T-cell type, including the present case. Interestingly, about half of HHV8-negative and HHV8-positive cases had a history of renal transplantation in their twenties. All cases showed tumor CD30 expression, whereas CD4 and CD8 expressions were inconsistent. These findings indicated that this lymphoma may be associated with post-transplant lymphoproliferative disorder by renal transplantation at a young age, although further cases need to be analyzed.

Molecular epidemiology of human herpesvirus 8 in patients with HHV-8-related diseases in Ireland.

Human Herpesvirus 8 (HHV-8) has been classified by sequence analysis of open reading frame (ORF) K1, ORF K15, and variable sequence loci within the central constant region. The purpose of this study was to examine the molecular epidemiology of HHV-8 in an Irish population. This retrospective study included 30 patients who had HHV-8 DNA detected in plasma. Nested end-point PCR was used to characterise four regions of the HHV-8 genome, K1, T0.7 (K12), ORF 75, and K15. Sequencing data were obtained for 23 specimens from 19 patients. Phylogenetic analysis of ORF K1 demonstrated that subtypes A, B, C and F were present in 37%, 11%, 47% and 5%, respectively. For T0.7 and ORF 75, sequencing data were obtained for 12 patients. For T0.7, subtypes A/C, J, B, R and Q were present in 58%, 17%, 8%, 8%, and 8%, respectively. For ORF 75, subtypes A, B, C and D were present in 58%, 8%, 25%, and 8%, respectively. K15 sequences were determined for 13 patients. 69% had the P allele and 31% had the M allele. The data generated by this study demonstrate that a broad variety of HHV-8 subtypes are represented in patients exhibiting HHV-8-related disease in Ireland, a low prevalence country. The predominance of C and A K1 subtypes was as expected for a Western European population. The 31% prevalence for K15 subtype M was higher than expected for a Western European population. This may represent the changing and evolving epidemiology in Ireland due to altered migration patterns.

Kaposi sarcoma in an individual recently diagnosed with HIV.

Kaposi Sarcoma (KS) commonly manifests with multiple vesicular cutaneous and mucosal nodules, with four subtypes clinically recognized. Although commonly seen in younger men, our patient presented with presumed epidemic KS at an older age. Additionally, our patient presented with Kaposi sarcoma during primary HIV infection which is atypical for Kaposi sarcoma presentation. The patient's clinical course is important to follow, as his rectal involvement indicates the patient would benefit from systemic therapy. Furthermore, our case highlights the need for a keen clinical index of suspicion in all patients with new HIV diagnosis and new onset suspicious lesions, regardless of age.

Prognostic factors in Kaposi sarcoma, single centre experience.

BACKGROUND: Kaposi sarcoma (KS) is a multicentric vascular and lymphatic neoplasm caused by human herpesvirus 8 (HHV-8). It generally concerns the elderly and immunosuppressed population. Four major clinical types of KS have been described. The most common subtype is Classical KS (CKS). OBJECTIVES: Our retrospective study aimed to better define prognostic subgroups among patients with CKS, which is the most common in our country. METHOD: Between 2014 and 2020, 43 patients with CKS were treated with local excision, radiotherapy and chemotherapy. Reviewed information included demographics, clinical features, laboratory findings, treatment responses and overall survival. RESULTS: During the follow-up, eight patients (18.6%) died of CKS. The complete response rate was 46.5%, partial response and stable disease 51.2%, and progressive disease 2.3% of all patients. Gender, haemoglobin level at diagnosis, and disseminated involvement were prognostic factors affecting survival in all patients. CONCLUSION: We confirmed that male gender, low haemoglobin levels, and disseminated involvement are associated with poor prognosis in CKS patients. It is the only Turkish study in which prognostic analysis was performed for this rare cancer.

Human Herpesvirus 8-Positive Multicentric Castleman Disease in an Immunocompetent Patient: A Diagnostic Challenge.

We present a clinical case of a 79-year-old male admitted to inpatient care for longstanding asthenia and respiratory symptoms. Associated features were polyserositis, multiple enlarged lymphatic nodules, acute kidney injury, and heart failure. The patient's recent medical history revealed SARS-CoV-2 vaccination a week prior and an upper respiratory tract infection. The laboratory results from thoracentesis were compatible with a transudate, with no immunological stain. Epstein-Barr virus polymerase chain reaction (PCR) was positive. The thoracic, abdominal, and pelvic CT scans revealed multiple enlarged lymphatic nodules, worsening the pre-existent polyserositis and hepatosplenomegaly. The patient began to show signs of neurologic symptoms and deterioration of the global health status. An enlarged lymphatic nodule was excised and the pathology showed human herpesvirus 8 multicentric Castleman disease. The disease evolved rapidly into hematological dysfunction and blood transfusions were necessary. Even though the patient was started on high-dose rituximab therapy combined with etoposide, the disease evolved into multiorgan dysfunction with a fatal outcome.

Molecular Features of HHV8 Monoclonal Microlymphoma Associated with Kaposi Sarcoma and Multicentric Castleman Disease in an HIV-Negative Patient.

Human herpesvirus 8 (HHV8)-associated diseases include Kaposi sarcoma (KS), multicentric Castleman disease (MCD), germinotropic lymphoproliferative disorder (GLPD), Kaposi sarcoma inflammatory cytokine syndrome (KICS), HHV8-positive diffuse large B-cell lymphoma (HHV8+ DLBCL), primary effusion lymphoma (PEL), and extra-cavitary PEL (ECPEL). We report the case of a human immunodeficiency virus (HIV)-negative male treated for cutaneous KS, who developed generalized lymphadenopathy, hepatosplenomegaly, pleural and abdominal effusions, renal insufficiency, and pancytopenia. The excised lymph node showed features of concomitant involvement by micro-KS and MCD, with aggregates of HHV8+, Epstein Barr virus (EBV)-negative, IgM+, and lambda+ plasmablasts reminiscent of microlymphoma. Molecular investigations revealed a somatically hypermutated (SHM) monoclonal rearrangement of the immunoglobulin heavy chain (IGH), accounting for 4% of the B-cell population of the lymph node. Mutational analyses identified a pathogenic variant of KMT2D and variants of unknown significance in KMT2D, FOXO1, ARID1A, and KMT2A. The patient died shortly after surgery. The histological features (HHV8+, EBV-, IgM+, Lambda+, MCD+), integrated with the molecular findings (monoclonal IGH, SHM+, KMT2D mutated), supported the diagnosis of a monoclonal HHV8+ microlymphoma, with features intermediate between an incipient HHV8+ DLBCL and an EBV-negative ECPEL highlighting the challenges in the accurate classification of HHV8-driven lymphoid proliferations.

Primary Effusion Lymphoma Secondary to Human Herpesvirus 8 (HHV-8) Infection in an Immunocompetent Host: A Case Report.

Primary effusion lymphoma (PEL) is a rare, aggressive, mature type of B-cell lymphoma that usually causes malignant, lymphomatous effusions in the absence of a solid mass. This is commonly seen in immunosuppressed individuals such as those with underlying malignancies, human immunodeficiency virus infection (HIV), cirrhosis, and a history of solid organ transplantation who are infected with human herpesvirus 8 (HHV-8). Clinical presentation varies depending on the extent of disease like shortness of breath, abdominal distention, and typical B symptoms like weight loss, fever, and night sweats. Morphological and immunohistochemical analysis of pleural fluid is required for diagnosis of PEL. Recent case studies are increasingly being reported with cases of PEL presenting in immunocompetent individuals infected with HHV-8. We present a case of PEL in an immunocompetent host and highlight its presentation, diagnosis, and management approaches. Due to the well-known association of PEL with immunocompromised status, the diagnosis is often overlooked in immunocompetent individuals. This case would further highlight the increasing association and the need for clinical vigilance in diagnosing PEL in immunocompetent patients.

Gastrointestinal Kaposi: A Rare Case Unveiling the Presentation and Management Challenges of an Uncommon Neoplasm in the Digestive Tract.

Gastrointestinal Kaposi's sarcoma (GI-KS), which is frequently observed in individuals with HIV/AIDS, tends to manifest with vague symptoms or may not show any symptoms at all. These symptoms can include abdominal discomfort, nausea, vomiting, and low levels of iron in the blood, and they may worsen as the tumor enlarges, leading to more severe issues such as blockage or perforation of the bowel. Diagnosis usually requires an endoscopy to confirm the presence of GI-SK in individuals showing symptoms. In this case report, we describe a 29-year-old Hispanic male with vague symptomatology, anemia, and a probable unknown bleeding site.

HHV8-Positive Multicentric Castleman's Disease and Thrombotic Thrombocytopenic Purpura among HIV-Positive Patients.

Castleman's disease (CD) and thrombotic thrombocytopenic purpura (TTP) are rare diseases that can affect the general population, especially those with HIV. Owing to their rarity, the association between CD and TTP remains insufficiently understood. In this study, we present a case of a 53-year-old patient with controlled HIV infection who presented with fever, lymphadenopathy, severe anaemia, and thrombocytopenia. After a series of tests, the diagnosis was concurrent human herpesvirus 8 (HHV8)-related multicentric CD (MCD) and TTP. Only four male patients were previously reported having this association, with HHV8 present in four and HIV in three patients, suggesting that coinfection with HHV8 and HIV is a pivotal factor in MCD with TTP occurrence. LEARNING POINTS: Castleman's disease (CD) and thrombotic thrombocytopenic purpura (TTP) are rare diseases, and their association remains extremely uncommon.We report a case of multicentric CD (MCD) with TTP in a 53-year-old male patient with HIV.Only five patients, including ours, have been reported as having both MCD and TTP, with all five having HHV8 and four having HIV. Thus, coinfection with HHV8 and HIV may be a potential pivotal factor in the occurrence of MCD with TTP.

The Possible Role of Pathogens and Chronic Immune Stimulation in the Development of Diffuse Large B-Cell Lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. The disease is very heterogeneous, with distinct genetic alterations in subtypes. The WHO 2022 5th edition classification identifies several minor groups of large B-cell lymphoma where the pathogenetic role of viruses (like EBV and HHV-8) is identified. Still, most cases fall into the group of DLBCL not otherwise specified (NOS). No review focuses only on this specific lymphoma type in the literature. The pathogenesis of this entity is still not fully understood, but several viruses and bacteria may have a role in the development of the disease. The authors review critical pathogenetic events in the development of DLBCL (NOS) and summarize the data available on several pathogenetic viruses and bacteria that have a proven or may have a potential role in the development of this lymphoma type. The possible role of B-cell receptor signaling in the microenvironment is also discussed. The causative role of the Epstein-Barr virus (EBV), human herpesvirus-8 (HHV-8), Hepatitis C virus (HCV), human immunodeficiency virus (HIV), Hepatitis B virus (HBV), and other viruses are explored. Bacterial infections, such as Helicobacter pylori, Campylobacter jejuni, Chlamydia psittaci, Borrelia burgdorferi, and other bacteria, are also reviewed.