CD 68 1 cells of monocyte y macrophage lineage in the environment of AIDS - associated and classic - sporadic Kaposi sarcoma are singly or doubly infected with human herpesviruses 7 and 6 B

Earlier studies have shown that Kaposi sarcomas contain cells infected with human herpesvirus (HHV) 6B, and in current studies we report that both AIDSassociated and classic-sporadic Kaposi sarcoma contain HHV-7 genome sequences detectable by PCR. To determine the distribution of HHV-7-infected cells relative to those infected with HHV-6, sections from paraffin-embedded tissues were allowed to react with antibodies to HHV-7 virion tegument phosphoprotein pp85 and to HHV-6B protein p101. The antibodies are specific for HHV-7 and HHV-6B, respectively, and they retained reactivity for antigens contained in formalin-fixed, paraffin-embedded tissue samples. We report that (i) HHV-7 pp85 was present in 9 of 32 AIDS-associated Kaposi sarcomas, and in 1 of 7 classical-sporadic HIV-negative Kaposi sarcomas; (ii) HHV-7 pp85 was detected primarily in cells bearing the CD68 marker characteristic of the monocytey macrophage lineage present in or surrounding the Kaposi sarcoma lesions; and (iii) in a number of Kaposi sarcoma specimens, tumor-associated CD68 monocytesymacrophages expressed simultaneously antigens from both HHV-7 and HHV-6B, and therefore appeared to be doubly infected with the two viruses. CD681 monocytesymacrophages infected with HHV-7 were readily detectable in Kaposi sarcoma, but virtually absent from other normal or pathological tissues that harbor macrophages. Because all of the available data indicate that HHV-7 infects CD41 T lymphocytes, these results suggest that the environment of the Kaposi sarcoma (i) attracts circulating peripheral lymphocytes and monocytes, triggers the replication of latent viruses, and thereby increases the local concentration of viruses, (ii) renders CD681 monocytesymacrophages susceptible to infection with HHV-7, and (iii) the combination of both events enables double infections of cells with both HHV-6B and HHV-7. In the last decade three hitherto unknown viruses designated human herpesviruses (HHV) 6A, 6B, and 7 have been shown to infect peripheral blood cells (1–3). Although HHV-6A and HHV-6B are closely related (4–6) they differ in human epidemiology and disease association. While HHV-6A has been isolated from a number of disease states, it has been associated with none (see refs. 7, 8). HHV-6B, a more common human pathogen, is associated with exanthem subitum of young children (9), and in immunocompromized adults it has been reported to cause more severe infections (10–13, see ref. 8). The virus can be recovered from T lymphocytes (1–3) and macrophages (14) and therefore is thought to remain in latent state in these cells. It can be induced in virologically negative lymphocyte cultures by infection with HHV-7 (15). Less is known about the association of HHV-7 infection with human diseases, despite the fact that the sequence of the entire genome has been reported recently (16). This virus causes widespread infections in young children of somewhat older age than those afflicted with HHV-6B, and on rare occasions it has been associated with exanthem subitum or febrile illness (17–21). The virus then persists in the body and is shed in the saliva (22–26). Mainly because HHV-7 has been isolated from peripheral blood lymphocytes and grows in CD41 T lymphocytes (3, 27, 28), and by analogy with HHV-6B, it has been postulated that HHV-7 is harbored in latent form in T lymphocytes. In vitro the susceptibility to HHV-7 is restricted to CD41 T lymphocytes (refs. 3 and 27, see ref. 29) and indeed the CD4 molecule appears to be a component of the viral receptor (30, 31). Attempts to infect terminally differentiated macrophages have not been successful (32). Unlike HHV-6B, which has been detected in a variety of cells, tissues, and disease states (10–13, 33–37), cells productively infected with HHV-7 have been reported only in salivary glands (22–26). In an attempt to define the conditions that lead to productive infection in other tissues, we analyzed AIDSassociated and classic-sporadic Kaposi sarcoma specimens in the expectation that in these tissues the reactivation frequency would be higher than in other normal or pathological tissues. Indeed, numerous herpesviruses, including HHV-6 and human cytomegalovirus (HCMV), have been detected in Kaposi sarcoma lesions (ref. 38, see ref. 39). For HHV-6, antigenic expression was detected (38). For HCMV, expression of viral antigens is controversial (see ref. 39). Research on HHV-7 has been impaired by difficulties in growing the virus in cell cultures and the scarcity of specific antibodies that differentiate between HHV-7 and HHV-6. The major proteins specific for HHV-7-infected cells were identified by means of mouse and rabbit polyvalent sera and a few mAb (40). Two mAbs (5E1 and 3B1) recognize a family of at least five antigenically related proteins with apparent Mr of 87,000, 85,000, 70,000, 61,000, and 57,000 (40). Of these the Mr 85,000 species designated pp85 is phosphorylated (41). The proteins of the pp85 complex are located to the virion tegument (41). Phosphoprotein 85 is the immunodominant HHV-7 antigen in the human population (42, 43). We report that with the aid of mAb 5E1 we detected the presence of HHV-7 pp85 in CD681 monocytesymacrophages present in Kaposi sarcoma lesions. This mAb is particularly suitable for in situ detection of HHV-7 productive infection inasmuch as it reacts with a conformation-independent epitope of an abundant, HHV-7-specific tegument protein. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ‘‘advertisement’’ in accordance with 18 U.S.C. §1734 solely to indicate this fact. © 1997 by The National Academy of Sciences 0027-8424y97y947600-6$2.00y0 PNAS is available online at http:yywww.pnas.org. Abbreviations: HHV, human herpesvirus; HCMV, human cytomegalovirus; IHC, immunohistochemistry. ‡Present address: Heart Center, University Leipzig, 04289 Leipzig, Germany ¶To whom reprint requests should be addressed at: Dipartimento di Patologia Sperimentale, Sezione di Microbiologia e Virologia, Via San Giacomo, 12, 40126 Bologna, Italy. e-mail: campadel@ kaiser.alma.unibo.it