Differential cellular targets of Epstein-Barr virus (EBV) infection between acute EBV-associated hemophagocytic lymphohistiocytosis and chronic active EBV infection

Unusual Epstein-Barr virus (EBV) infection into T or natural killer cells plays a pivotal role in the pathogenesis of acute EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) and chronic active EBV infection (CAEBV). The precise frequency and localization of EBV genome in lymphocyte subpopulations especially within T-cell subpopulations are unclear in these EBV-related disorders. This study analyzed the frequency of EBV-infected cells in circulating lymphocyte subpopulations from 4 patients with acute EBV-HLH and 4 with CAEBV. EBV- encoded small RNA-1 in situ hybridization examination of peripheral blood lymphocytes showed a significantly higher frequency of EBV-infected cells of 1.0% to 13.4% in EBV-HLH and 1.6% to 25.6% in CAEBV, respectively. The patterns of EBV infection in lymphocyte subpopulations were quite different between acute EBV-HLH and CAEBV. EBV infection was predominant in CD8(+) T cells in all EBV-HLH patients, whereas the dominant EBV-infected cell populations were non-CD8(+) lymphocyte subpopulations in CAEBV patients. Phenotypical analysis revealed that EBV-infected cell populations from both EBV-HLH and CAEBV were activated. There was no predominance of any EBV substrain of latent membrane protein-1, EBV-associated nuclear antigen (EBNA)-1, and EBNA-2 genes between the 2 abnormal EBV-associated disorders, and self-limited acute infectious mononucleosis. These results showing differential virus-cell interactions between acute EBV-HLH and CAEBV indicated different pathogenic mechanisms against EBV infection between the 2 EBV-associated diseases, which accounts for the difference in clinical manifestations between the 2 diseases.

Increased cell-free viral DNA in fatal cases of chronic active Epstein-Barr virus infection

We have studied the nature of Epstein-Barr virus (EBV) infection in 33 patients with chronic active EBV infection. The study population included 14 patients with fatal chronic EBV infection and 19 patients with nonfatal chronic EBV infection, as well as 18 patients with acute EBV-induced infectious mononucleosis and 10 healthy controls. EBV DNA was measured in serum or plasma samples from the patients by semiquantitative polymerase chain reaction-based assay. EBV DNA was detected in serum or plasma samples from 62% (9/14) of patients with fatal chronic active EBV infection. In contrast, only 11% (2/19) of patients with nonfatal chronic active EBV infection and 11% (2/18) of patients with infectious mononucleosis displayed EBV DNA. None of the healthy controls tested positive. Cell-free circulating EBV DNA may represent an important feature of chronic active EBV infection and may provide a useful tool to monitor the severity of this illness.

Contribution of the CXC chemokines IP-10 and Mig to the antitumor effects of IL-12

The mechanisms by which interleukin-12 (IL-12) exerts antitumor effects have been difficult to dissect. In this study, we examined the potential contribution of the chemokines interferon-gamma-inducible protein-10 (IP-10) and Mig to the antitumor effects of IL-12. Using an athymic mouse model, local inoculations with IL-12 consistently produced tumor size reductions associated with characteristic tumor necrosis and vascular damage. These effects were indistinguishable from those produced by IP-10 or Mig injected locally in the same tumor model. Local and systemic treatment with IL-12 was associated with expression of the interferon-gamma (IFN-gamma), IP-10, and Mig genes and proteins in the tumor. Levels of IP-10 and Mig expression in the tumor, the liver, and the kidney were inversely correlated with tumor size. Administration in vivo of neutralizing antibodies to IP-10 and Mig reduced substantially the antitumor effects of IL-12 inoculated locally into the tumors. These results support the notion that IP-10 and Mig contribute to the antitumor effects of IL-12 through their inhibitory effects on tumor vasculature.

Expression of the Epstein-Barr virus protein LMP1 mediates tumor regression in vivo

By stimulating the expression of murine IP-10 and Mig, CXC chemokines that inhibit neovascularization and cause damage to established tumor vasculature, human B cells immortalized with Epstein-Barr virus (EBV) can promote an effective antitumor response in athymic mice. In the present study, we examined the potential role of EBV in the induction of this antitumor response. Using a panel of EBV+ and EBV- Burkitt lymphoma (BL) cell lines, a significant correlation was detected between the expression of the EBV latency gene LMP1 and the occurrence of spontaneous tumor regression in athymic mice. Inoculation of LMP1+ and LMP1- BL cells in the same subcutaneous site resulted in tumors that completely regressed in a manner indistinguishable from that induced by EBV-immortalized B cells. EBV-converted BL30 and BL41 sublines infected with B95-8 virus expressed LMP1, generated tumors that frequently regressed spontaneously, and promoted an effective antitumor response against progressively growing tumors. In contrast, the EBV- BL30 and BL41 cell lines and the EBV-converted BL30 and BL41 infected with P3HR-1 virus did not express LMP1 protein, and generated progressively growing tumors in nude mice. When transfected with the LMP1 gene, BL41 cells produced tumors that regressed spontaneously in most cases, and could induce the regression of tumors derived from BL41 cells transfected with vector alone. Tumors induced by LMP1-expressing cells expressed murine IP-10 and Mig and displayed histological evidence of extensive tumor tissue necrosis and vascular damage. We conclude that the EBV protein LMP1 is likely responsible for the antitumor response elicited by EBV-immortalized cells in athymic mice.

Viral interleukin-10 in chronic active Epstein-Barr virus infection

Viral interleukin-10 (IL-10), a product of the Epstein-Barr virus (EBV) replication gene BCRF1, shares extensive structural and functional similarity with the human cytokine IL-10. Both viral and human IL-10 inhibit T cell growth and interferon-gamma production. With two ELISAs, one that recognized both human and viral (total) IL-10 and the other specific for viral IL-10, IL-10 was measured in serum or plasma from 34 patients with chronic active EBV infection (CAEBV) and from 15 healthy controls. Of the patients, 56% had measurable total IL-10 and 29% had measurable viral IL-10. In contrast, total IL-10 was detectable in only 2 of 15 controls and viral IL-10 was undetectable. Thus, many patients with CAEBV have abnormally high levels of circulating IL-10 that may contribute to disease pathogenesis by inhibiting host immunity.

Mig, the monokine induced by interferon-gamma, promotes tumor necrosis in vivo

Mig, the monokine induced by interferon-gamma, is a CXC chemokine active as a chemoattractant for activated T cells. Mig is related functionally to interferon-inducible protein 10 (IP-10), with which it shares a receptor, CXCR3. Previously, IP-10 was found to have antitumor activity in vivo. In the present study, murine Mig RNA was found to be expressed at higher levels in regressing Burkitt's lymphoma tumors established in nude mice compared with progressively growing tumors. Daily inoculations of purified recombinant human Mig into Burkitt's tumors growing subcutaneously in nude mice consistently caused tumor necrosis associated with extensive vascular damage. These effects were indistinguishable from those produced by intratumor inoculations of Burkitt's tumors with IP-10. These results support the notion that Mig, like IP-10, has antitumor activity in vivo.

Infectious mononucleosis as a disease of early childhood in Japan caused by primary Epstein-Barr virus infection

The present study investigated 54 pediatric patients with acute Epstein-Barr virus (EBV)-induced infectious mononucleosis (IM) in Japan. Most of the acute cases clustered within the first 5 years of life, and the peak incidence was observed at around 4 years of age. These patients were arbitrarily separated into three age groups (less than 3 years, 3-5 years, and 6-14 years). Fever, pharyngitis, lymphadenopathy and hepatomegaly were detected in more than 80% of all cases. Tonsillitis and splenomegaly were present in about 60% of cases. Skin manifestations and eyelids edema were less often detected in the older age group than in the young age groups. In addition to an increase of total white blood cell and lymphocyte counts in the peripheral blood, a significant increase in the percentage of CD3+ CD8+ HLA-DR+ T cells was always observed. Epstein-Barr virus seropositivity increased soon after birth and reached approximately 70% around 3 years of age. Close to 100% of the adult controls were EBV seropositive. The results suggest that EBV-induced acute IM is a disease of early childhood in Japan.

Infective endocarditis caused by an unusual gram-negative rod, Rahnella aquatilis

An 11-month-old girl with congenital heart disease developed infective endocarditis. Blood cultures revealed an unusual gram-negative rod, Rahnella aquatilis. The patient was successfully treated with a combination of netilmicin and ceftazidime. This is the first case report of infective endocarditis caused by this organism. R. aquatilis should be recognized as a clinical pathogen capable of causing life-threatening infection in children and adults.

Mononucleosis-like illness in an infant associated with human herpesvirus 6 infection

Illnesses resembling mononucleosis, hematologically characterized by atypical lymphocytosis in the peripheral blood, are caused by other viral infections as well as by a primary Epstein-Barr virus infection. Human herpesvirus 6, a newly isolated member of the herpesvirus group, can also cause a mononucleosis-like illness. Illness associated with human herpesvirus 6 infection mostly occurs in immunocompetent adults. We observed a 3 month old infant who presented with marked atypical lymphocytosis and liver dysfunction. We examined serum samples to detect viral antibodies related to mononucleosis-like illness. Only the titers of antibody against human herpesvirus 6 were elevated. Primary human herpesvirus 6 infection cannot only cause exanthem subitum or present in an inapparent form but can also cause an illness like mononucleosis, even in an infant.