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The authors report an unusual case of herpes simplex type 2 (HSV) hepatitis which presented as part of a systemic HSV infection accompanied by disseminated intravascular coagulation (DIC). The patient was a 49-year-old Japanese male who three months prior to admission underwent surgical resection of his thymus for an invasive thymoma. Postoperatively, he received a course of chemotherapy which included prednisone, cyclophosphamide, vincristine, and pinorubicin. After discharge from the hospital, he was put on a maintenance dosage of prednisone and cyclophosphamide. Two weeks prior to this admission, the patient developed rhinorrhea, chills and general fatigue. Routine follow-up laboratory tests revealed markedly elevated liver enzymes which led to his immediate hospitalization. The tentative diagnosis on admission was fulminant hepatitis with DIC. The patient’s condition steadily worsened during his hospitalization and acyclovir was initiated on the 4th hospital day due to the possibility of HSV hepatitis. He died on the same day. Histopathology performed on the liver at autopsy revealed hepatic inclusion bodies of HSV with positive immunohistochemical detection of the HSV type 2 antigen. Our case is the first report of HSV hepatitis associated with the removal of the thymus secondary to thymoma. It supports previous observations of disseminated HSV infection being prevalent in those patients with disorders of cell mediated immunity.

Human herpesvirus 6 (HHV-6), the causative agent of exanthem subitum, has been implicated in other diseases. Recently HHV-6-specific sequences have been detected by Southern blot analysis and polymerase chain reaction in the lymph nodes of three patients with Hodgkin's disease. The pathological localization of HHV-6, however, is still unknown. In order to study the pathological role of HHV-6 in Hodgkin's disease, we investigated, by immunohistochemical and molecular methods, two lymph node biopsies taken from a 7-year-old boy with Hodgkin's disease during the course of disease evolution. Although the histopathological findings of the first biopsy differed from those of the second, HHV-6 antigens and sequences could be detected in both lymph nodes by immunohistochemistry and in situ hybridization, respectively. HHV-6 was localized in macrophages, predominantly in lymphoid follicles, but not in Reed-Sternberg cells. Antibody titres to HHV-6 were consistent with reactivation of latency. Neither cytomegalovirus nor Epstein-Barr virus was present. Our data suggest a role for HHV-6 in the pathogenesis of Hodgkin's disease.

We established a murine monoclonal antibody (K1H8) to human papillomavirus (HPV) using alkaline-disrupted virions of HPV type 1 (HPV-1) as the immunogen. K1H8 recognized a 57 kD capsid protein of HPV-1 and detected the antigen in paraffin sections of formalin-fixed tissue. With K1H8, we examined immunohistochemically 68 biopsy specimens obtained from the female genital tract. The specimens were histologically condyloma acuminatum or koilocytotic lesions with or without dysplasia and each specimen was found to harbour a single type of genital HPV, such as types 6, 11, 16, 18, 31, 33, 42, 51, 52, 56, and 58, by Southern blot hybridization analysis. The antigen was localized in the nuclei and occasionally in the cytoplasm of squamous cells showing koilocytotic changes. Eighty-four per cent of the specimens (57 cases) showed positivity for the antigen, indicating that K1H8 is a broadly-reactive antibody to various genital HPVs. The results suggest that benign mucosal lesions of the female genital tract are more frequently associated with viral production and are a potential source of transmission.

A simple method using field-inversion gel electrophoresis (FIGE) was applied to detect herpes simplex virus (HSV) and varicella-zoster virus (VZV) genomes in clinical specimens. The whole genomes of these viruses could be detected in small vesicle tissues by the FIGE method regardless of their clinical stages of skin lesions. And the sensitivity of the FIGE method was equivalent to that of an immunofluorescent (IF) method. These data indicated usefulness of the FIGE method to detect the whole genomes of HSV and VZV in clinical specimens.

Thirty-seven biopsy skin tissues of herpes zoster taken from 27 patients were analysed immunohistochemically using two monoclonal antibodies detecting either nucleocapsid or glycoproteins of varicella-zoster virus (VZV) on paraffin sections of formalin fixed tissues. Skin lesions of herpes zoster were divided clinically into four stages: erythematous, vesicular, pustular and ulcerative. In the erythematous stage, VZV antigens, if detected, were found only within ballooning cells in the lower epidermis or follicular epithelium. In the vesicular stage, antigens were detected in the cells around and within the intraepidermal vesicles and in histiocytes or fibrocytes of the dermis in all cases and in the endothelial or perineural cells in 10 of 14 cases. In the pustular stage, the antigens were observed in degenerated or necrotic keratinocytes and multinucleated giant cells within pustules and some necrotic cells in the dermis. In the ulcerative stage, the viral antigens were detected only at the ulcer margin and around the hair shaft in 2 of 7 cases. These results suggest that VZV initially involves the epidermis in the erythematous stage, subsequently invades the dermis in the vesicular stage, and disappears in the early ulcerative stage.

A case of fetal death at 25 weeks' gestation, which was associated with maternal measles infection, is described. Immunohistochemical study revealed measles virus antigen in the syncytial trophoblastic cells and decidua but not in the fetus. Results suggest that fetal death was caused by measles virus infection in the placenta. As far as we know, this is the first report in which a measles virus antigen was detected in the placenta by the immunohistochemical method.

The lectin amaranthin, purified from the seeds of Amaranthus caudatus, has been shown to react specifically with the Gal beta 1,3GalNAc-alpha and the NeuAc alpha 2,3Gal beta 1,3GalNAc-alpha sequence which represent the T antigen and the cryptic T antigen, respectively. We report here the development of labeling techniques that apply amaranthin to stain paraffin sections from rat fetuses. Amaranthin staining was inhibited by pre-incubation of lectin-gold complexes with 10 mM Gal beta 1,3GalNAc-alpha-O-benzyl (synthetic T antigen) or 10 mM Gal beta 1,3GalNAc-alpha-O-aminophenylethyl-human serum albumin (T antigen neoglycoprotein), asialoglycophorin, asialofetuin, and asialomucin. The beta-elimination reaction also abolished the lectin staining demonstrating specificity for O-glycosidically linked structures. A comparison with monoclonal anti-T antigen antibody immunostaining demonstrated that amaranthin detects the T antigen and its cryptic form in tissue sections. Application of the galactose oxidase-Schiff sequence abolished amaranthin (and anti-T antibody) binding to the T antigen but not to its cryptic form, and therefore permitted their differentiation in tissue sections. Histochemical evidence was obtained indicating that amaranthin is a more specific anti-T reagent than peanut lectin. Data are presented that show the differential expression of the T antigen and the cryptic T antigen in organs and cells of rat fetuses late in gestation. Therefore, amaranthin can be used for histochemical detection of the T antigen and the cryptic T antigen, and facilitates discrimination between them.

We report the use of a novel hapten system for lectin cytochemistry. Various lectins conjugated to the steroid hapten digoxigenin (DIG) and monospecific anti-digoxigenin antibodies were applied for the light and electron microscopic detection of glycoconjugates in tissue sections. Both IgG and Fab' anti-DIG antibodies were complexed to particles of colloidal gold and compared to commercially available alkaline phosphatase and horseradish peroxidase conjugated Fab' as general second step reagents. The three different markers performed equally well on paraffin sections whereas the gold-labeled antibodies were superior reagents for semithin and ultrathin sections of Lowicryl K4M embedded tissues. In conjunction with the latter marker, no pretreatment to abolish endogenous enzyme activity was necessary. At the light microscope level, gold signal amplification by the photochemical silver reaction was required. DIG, in contrast to biotin, does not occur in animal tissues thus eliminating the need for blocking reactions prior to lectin incubation. Compared to affinity techniques using glycoprotein-gold complexes as second step reagent the DIG hapten system required smaller amounts of lectins. The staining patterns were indistinguishable from those obtained in other lectin-gold techniques and the specificity of the labeling could be demonstrated in sugar inhibition tests.

Anti-varicella zoster virus (VZV) mouse monoclonal antibodies conjugated with fluorescein isothiocyanate were evaluated for their usefulness as a practical diagnostic tool in the clinical field by examining cells infected with isolated herpes viruses and 431 clinical samples. The kit stained clearly the cells infected with 14 isolated VZV strains without cross reaction to 15 isolated herpes simplex virus type-1 strains (HSV-1) and 14 type-2 (HSV-2) strains. In clinical specimens, viral antigens of VZV were detected in 92/105 (87.6%) cases of varicella and in 176/190 (92.6%) cases of herpes zoster. Specific fluorescence of VZV was also observed in 5 out of 96 cases diagnosed as HSV infections, although these samples had no specific reaction to HSV when tested by the commercially available diagnostic kit. In 24 cases which could not be clinically diagnosed as herpes zoster or herpes simplex, the VZV antigen was demonstrated in 9 cases. All 109 VZV-positive cases in virus isolation by culture were also judged VZV-antigen positive by the kit, while all 69 HSV-positive cases in virus isolation were VZV-antigen negative. Furthermore, the VZV antigen was detected by the kit in 53/60 clinical diagnoses of varicella or herpes zoster without successful virus isolation. These results clearly indicate the usefulness of the kit as a practical VZV diagnostic reagent, especially in terms of specific sensitivity and easy technical manipulation.

PEL is a rare B-cell neoplasm characterized by a preferential involvement of fluid-filled body spaces, consistent infection of the tumor clone by human herpesvirus type-8 (HHV-8) and a close relationship with underlying immunodeficiency status of the host. The International Extranodal Lymphoma Study Group (IELSG) coordinated a retrospective survey involving 15 international institutions to determine the clinico-pathological features and patterns of outcome of PEL. Fourty-three patients (38 males and 5 females) were registered. Median age at diagnosis was 59 years (range 27–102). In 23 (53%) patients an associated human immunodeficiency virus (HIV) infection was reported, in one case the diagnosis of PEL was made after a solid organ transplantation, in two patients other immunodeficiency conditions were present. The tumor HHV-8 infection was demonstrated in 35 out of the 39 tested cases, Epstein-Barr virus infection in 13 of 30 cases. CD4 count was lower than 200/μl in 18 of the 25 cases in whom the data was available. An ECOG perfomance status score ≥ 2 was observed in 29 patients and the presence of B-symptoms in 20 patients. Serum LDH was elevated in 21 of the 39 tested patients. In 4 patients nodal involvement at diagnosis was reported, in 4 cases at least one extranodal site of localization other than serous cavities was present. A low/low-intermediate risk score according to International Prognostic Index was reported in 10 cases, an intermediate-high/high risk score in 29 cases. Twenty-one patients received systemic chemotherapy, in 17 cases an anthracycline-based regimen. Intrapleural cidofovir was administered in 3 patients. Twelve HIV+ patients received highly active anti-retroviral therapy (HAART), four of them as single therapy. Among the 39 patients for whom adequate follow-up data were available, median overall survival was 6.7 months, median cause-specific survival was 13.6 months and median progression-free survival was 8.3 months. Interestingly, cases of tumor complete regression after implementation of the sole HAART, after intrapleural administration of cidofovir or without any treatment were reported. Our data confirm the poor prognosis of PEL but suggest a possible heterogeneity of this entity with respect to its biological and clinical features. A review of the pathological, phenotypical and virological features is forthcoming to validate these preliminary results.

Objective To identify distinct clinical features of pharyngotonsillitis or oropharyngitis associated with Epstein-Barr virus (EBV) infection from herpes simplex virus infection. Design Clinical studies by case exploration. Setting Institutional practice at a university hospital. Patients Thirty-three patients with pharyngotonsillitis and 4 patients with oropharyngitis of nonbacterial infection underwent biopsy of pharyngotonsillar lesions. Main Outcome Measure The specimens were examined by histopathology, immunohistochemistry, in situ hybridization, and polymerase chain reaction. In addition to serological testing and routine laboratory data, photographic oropharyngeal findings were collected for clinical evaluation. Results In situ hybridization to detect EBV-encoded small nuclear RNA-1 and -2 disclosed 8 cases of pharyngotonsillitis and 4 cases of oropharyngitis associated with EBV infection. Immunohistochemical analysis identified 5 cases of pharyngotonsillitis associated with herpes simplex virus infection. Serological examination showed that, among 12 cases positive by in situ hybridization, 3 cases were primary infection with infectious mononucleosis and 9 were nonprimary infection. The staining pattern of in situ hybridization was different, ie, a linear pattern in cases of nonprimary infection and a scattered pattern in cases of primary infection. The clinical manifestations of EBV pharyngotonsillitis were distinct from those of herpes simplex virus pharyngotonsillitis and were characteristic irrespective of infectious status, while those of EBV oropharyngitis were more variable. Conclusions Epstein-Barr virus–associated pharyngotonsillitis was demonstrated in patients with nonprimary infection unaccompanied by infectious mononucleosis. Epstein-Barr virus should be considered a potential causative agent of oropharyngotonsillitis even in absence of infectious mononucleosis, especially in a young adult.

As the pathogenesis of Bell's palsy, herpes simplex virus (HSV) infection has been suggested on the basis of several serological studies. To clarify and analyse the pathogenic mechanisms of this disease, guinea pigs were inoculated with type-1 HSV through natural infection routes into the peripheral areas innervated by facial nerve, and nervous tissues were examined by histopathological and immunohistochemical methods. HSV-I infection in the nasal mucosa, tongue, oral muscles and auricles brought about neither clinical facial palsy nor disturbed Preyer or corneal reflexes, but viral antigens in the inoculated peripheral areas, facial and trigeminal ganglia and pons with inflammatory cell response, hemorrhages and degeneration and necrosis. Cyclophosphamide treatment resulted in disturbed Preyer and corneal reflexes and enhanced the incidence of antigen appearance and histopathological changes.

An autopsy case of necrotizing pancreatitis with cytomegalovirus (CMV) infection is reported. A 50-year-old housewife was admitted because of malignant choroid plexus papilloma of the fourth ventricle. Serum amylase transiently elevated during irradiation and chemotherapy for brain tumor, one month before death. The patient died of a respiratory failure. At autopsy focal necrosis was mainly observed in the peripancreatic adipose tissue and occasionally in the parenchyma of the tail. Fibrosis and inflammatory infiltration was found around the necrosis and interstitium. Cytomegalic cells with intranuclear inclusions and/or cytoplasmic granules were observed frequently in the acini near the necrosis. Immunohistological study revealed CMV antigen in the cytomegalic cells. Herpesvirus-type particles were observed in the nucleus and cytoplasm of the cytomegalic cells. CMV infection of the acini are thought to cause necrotic changes in the pancreas.

Ovarian involvement of cytomegalovirus (CMV) is rarely observed in autopsy and biopsy materials. Cortical necrosis of the ovaries was found in an autopsy case with generalized CMV infection. The patient was an 11-year-old girl in a remission state of acute lymphocytic leukemia. Autopsy revealed several areas showing necrotic change up to 2 mm in size in the cortex of both ovaries. Many cytomegalic cells were found in both the necrotic and intact areas of the cortex. CMV had infected the granulosa, thecal and stromal cells as well as vascular endothelial cells. Oocytes of neither primary nor graafian follicles showed cytomegalic changes, although they were destroyed due to the necrosis. CMV antigen was immunohistologically detected in these cytomegalic cells. Ultrastructurally, herpesvirus-type particles were revealed in the nuclei and cytoplasm of the cytomegalic cells. This case demonstrated that ovarian infection with CMV can potentially induce cortical necrosis and decrease the number of oocytes.

Herpes simplex virus 1 (HSV-1) UL13 is a viral protein kinase that is packaged into virions and regulates optimal expression of ICP0 and a subset of late (γ) proteins, including UL41 in infected cells. In the present study, we investigated the role(s) of the protein kinase activity of UL13 in viral replication using a recombinant virus expressing enzymatically inactive UL13 after an amino acid substitution in the invariant lysine of UL13. The recombinant virus carrying this mutation formed smaller plaques yielded 10-fold less progeny than wild-type virus but could not be differentiated from wild-type virus with respect to accumulation of UL41 and ICP0 in infected cells. These results indicate that the protein kinase activity of UL13 plays a role in viral replication in cell culture, but the activity is not essential for the optimal expression of UL41 and ICP0.

To investigate the expression of human herpesvirus 8 (HHV8)-encoded proteins in the cells of primary effusion lymphoma (PEL), Kaposi's sarcoma (KS) and multicentric Castleman's disease (MCD), nine rabbit polyclonal antibodies to K2, ORF26, K8, K8.1, K10, K11, ORF59, ORF65, and ORF73 were developed. Western blot analysis in PEL cell lines (TY-1 and BCBL-1) revealed that the expression of these proteins, except ORF73 (LANA), was induced by tetradecanoylphorbol acetate (TPA) treatment, indicating that these proteins are lytic proteins. Immunofluorescence assay in primary PEL cells derived from pericardial effusion and PEL cell lines with and without TPA treatment revealed that primary PEL cells exhibited the same expression pattern as noninduced PEL cell lines, and the treatment changed localization of K8, ORF59, and ORF65 proteins. Immunohistochemistry revealed that 90% of KS spindle cells expressed the ORF73 protein, whereas a small population of KS cells expressed K8, K10, K11, ORF59, and ORF65 proteins. In MCD, ORF73, ORF59, K8, K2, and K10 proteins were expressed in the cells at mantle zone of the follicle. These data indicate that KS and PEL cells expressed predominantly latent proteins, whereas MCD expressed both latent and lytic proteins, suggesting that HHV8 plays a different role in the pathogenesis of HHV8-associated diseases.

The pancreatic tissue from 131 human cases with fatal herpes infections were viropathoiogically examined for islet lesions. Diagnoses of all cases were confirmed by virus isolation, serological tests and immunohistochemistry. Focal or massive necrosis, including destruction of beta cells, intranuclear inclusion bodies and inflammatory changes in islets were found in 45 cases, in accordance with the existence of viral antigens. All pancreatic lesions were observed as the expression of a generalized herpesvirus infection and not as solitary damage appearing only in the pancreas. The findings suggest the participation of these viruses in damage to beta cells resulting in diabetes.

Mesangiolysis associated with glomerulomegaly was observed in an autopsy case of an 11-year-old boy with cyanotic congenital heart disease, i.e. complete transposition of the great vessels with large VSD. Microscopical examination of the kidney revealed marked enlargement of glomeruli with mesangiolysis mainly found in the midzonal cortex involving 16 to 20% of all glomeruli. The glomerular basement membrane in the mesangiolytic lesion showed splitting, between which red blood cells were occasionally encountered. By reconstruction study with serial sectioning, the mesangiolysis was observed to be obviously focal and segmental. Immunofluorescent study revealed no positive results for IgG, IgA, IgM, C3, and fibrinogen/fibrin. By electron microscopic study on the post formalin fixed specimens, no remarkable dense deposits were found in any structural components of the glomeruli. It was assumed that the mesangiolysis might have been provoked by some circulatory disturbances, which superimposed on the preexisting glomerular lesion of cyanotic congenital heart disease in the terminal stage of the clinical course.

The localization of measles virus proteins was analyzed by immunoperoxidase method using both monospecific and monoclonal antibodies. In Vero cells infected with the Edmonston or EB-L strain, the former being a laboratory strain and the latter a fresh isolate from a measles patient, nucleocapsid protein was located in the nuclei, and matrix protein, phosphoprotein, haemagglutinin and fusion protein were located in the cytoplasm. In the lung tissues of eight cases with measles giant cell pneumonia, the similar findings were obtained. The presence of haemagglutinin on the surface of giant cells at the luminal side was also noticed. Histopathologically, measles giant cells had nuclear and cytoplasmic eosinophilic inclusion bodies with some differences in appearance. The significance of localization of viral proteins is discussed in comparison with histopathological findings in measles giant cells.

An 8-month-old girl suffered from Letterer-Siwe disease since one week after birth. During the chemotherapy, giant cell pneumonia caused by measles virus infection developed and led rapidly to her death. Histopathologically, alveolar spaces were lined by multi-nucleated giant cells with intranuclear and intracytoplasmic eosinophilic inclusion bodies. Electronmicroscopical examination of the lung revealed intranuclear inclusion bodies full of rod-shaped structures characteristic to paramyxoviruses, and irregular electron-dense materials compatible with nucleocapsid protein antigens in the cytoplasm. Additionally these giant cells were observed in the salivary glands, thyroid gland, thymus and lymph nodes. The measles virus antigen was detected immunohistochemically in these giant cells in the lungs and other organs. The specific antibody of measles virus is helpful to study the pathogenesis of giant cell pneumonia.

By immunizing Prnp-knockout mice with synthetic polypeptides, a panel of mAbs directed to bovine PrP(C) was obtained. The mAb panel was characterized by the ELISA method, where synthetic polypeptides were used for epitope mapping. Different reactivity patterns were identified. The ability of these mAbs to detect abnormal PrP(Sc) in CJD cases was studied by immunohistochemistry. All mAbs were tested for PrP(Sc) in murine, bovine, monkey and human brain tissues. Three mAbs recognized the fragmented PrP epitope in our ELISA. Antibody 1D12 was strongly reactive to ovine and squirrel monkey tissues infected with a scrapie agent, although non-reactive to scrapie-infected mouse tissues. Antibody 2D8 was clearly reactive to type-2 but not type-1 CJD human tissues. Of particular interest was the reactivity of mAb 6C4 with the inner structure of Kuru plaques (peripheral pattern) in a type-2 CJD case and mAb T2, 1D12, 2B11, 2D8, 4B5 and 6G3-2 with the central area (central pattern). The fact that different anti-PrP mAbs possess distinct staining properties suggests that the PrP(c) to PrP(Sc) conversion might involve a multiple-step process.

The herpes simplex virus 1 (HSV-1) UL7 gene is highly conserved among herpesviridae. Since the construction of recombinant HSV-1 with a mutation in the UL7 gene has not been reported, the involvement of HSV-1 UL7 in viral replication has been unclear. In this study, we succeeded in generating a UL7 null HSV-1 mutant virus, MT102, and characterized it. Our results were as follows. (i) In Vero cells, MT102 was replication-competent, but formed smaller plaques and yielded 10- to 100-fold fewer progeny than the wild-type virus, depending on the multiplicity of infection. (ii) Using mass spectrometry-based proteomics technology, we identified a cellular mitochondrial protein, adenine nucleotide translocator 2 (ANT2), as a UL7-interacting partner. (iii) When ANT2 was transiently expressed in COS-7 cells infected with HSV-1, ANT2 was specifically co-precipitated with UL7. (iv) Cell fractionation experiments with HSV-1-infected cells detected the UL7 protein in both the mitochondrial and cytosolic fractions, whereas ANT2 was detected only in the mitochondrial fraction. These results indicate the importance of HSV-1 UL7's involvement in viral replication and demonstrate that it interacts with ANT2 in infected cells. The potential biological significance of the interaction between UL7 and ANT2 is discussed.

Adult T-cell leukemia (ATL) is a T-cell malignancy caused by HTLV-1. In ATL, chemotherapeutic responses are generally poor, which has suggested the existence of chemotherapy-resistant cancer stem cells (CSCs). The HTLV-I transactivator, Tax, initiates ATL-like disease (mATL) in Tax transgenic mice. Recently, the CSCs of mATL were identified. The CSCs in a side population, could consistently regenerate the original lymphoma and overlapped with a minor population of CD38(-)/CD71(-)/CD117(+) cells, suggesting that the eradication of cancer stem cells will be necessary to improve the outcome of treatment for mATL. In designing specific regimens for CSCs, antibody-based therapy appears to be a promising way to destroy CSCs. A small number of target antigens on cancer stem cells have been described. It remains to be determined, however, whether these and other targets will distinguish cancer stem cells from normal tissues. In this study, a proteomic approach was used to identify proteins differentially expressed in CSCs of mATL. The CSCs of mATL were isolated using cell sorting, and analyzed by label-free LC-MS/MS to compare protein profiles in CSCs and no-CSCs. More than 700 proteins were detected. The levels of 53 proteins were increased in CSCs. An interesting finding is that these proteins included one membrane protein, which might potentially serve as a new target of antibody-based therapy. Flow cytometry validated expression of the membrane protein. Taken together, the data presented provide a significant new protein-level insight into the biology of cancer stem cells of mATL, a key population which are involved in mATL development.

Background Alu elements are active non-LTR retrotransposons that account for approximately 11 % of the human genome and are known to be not only the cause of genetic disease in germinal cells, but have also been implicated on the development of B-cell lymphomas suggesting they affect the genome of somatic cells as well. In the present study, the molecular mechanisms of the inhibitory activity of human APOBEC3 (A3) family members on Alu retrotransposition were investigated. Materials and methods A3 family proteins were tested in a neomycin-resistant (neo r )-based retrotransposition assay. Briefly, HeLa cells were cotransfected with a neo r -Alu reporter vector, LINE-1 ORF2 vector and the respective A3 expression plasmids. Seventy-two hours post-transfection, G418 was added for resistance selection, and after 14 days resultant G418-resistant colonies were fixed, stained with crystal violet and counted. A series of APOBEC3G (A3G) mutants bearing deletions in the N-terminus in multiples of 30 amino acids (aa) were constructed to evaluate the responsible region. Likewise, dimerization and deamination deficient A3G mutants were also created to examine the inhibitory effect of A3G on Alu retrotransposition. Results The neo r -based retrotransposition assay showed that all hA3 family proteins differentially inhibited Alu retrotransposition. By the deletion analyses based on A3G that is the most well-characterized A3 family member, the N-terminal 30 aa of A3G was found to determine its inhibitory activity on Alu retrotransposition. Mutational analyses showed that the inhibitory activity of A3G was independent of its deaminase activity, but dependent on its dimerization, which was found to be affected by deletion in its N-terminal 30 aa. Importantly, the dimerization of A3G was also required for the inhibition of LINE-1 retrotransposition. Conclusions The N-terminal 30 aa of A3G are essential for its inhibitory activity on Alu retrotransposition, and this correlates with A3G homodimerization. The structural basis for the effect of the N-terminal 30 aa region of A3G on its dimerization is currently under investigation.