Royal pastel mink respond variously to inoculation with Aleutian disease virus of low virulence.

Information was sought on the varied responses of royal pastel mink (a non-Aleutian genotype) to Aleutian disease virus of low virulence. Thus, of 20 yearling female pastel mink inoculated subcutaneously with a large amount of the Pullman strain of Aleutian disease virus, only 3 succumbed to the disease. Of the other 17 mink, 3 had neither viremia nor a rise in level of serum gamma globulin during the 24 weeks after inoculation. The other 14 mink were viremic for variable periods during the first 12 weeks. In only five mink was the viremia accompanied by elevated levels of serum gamma globulin, usually from week 8 on. Of the 16 subclinically infected mink that did not succumb to intercurrent disease and otherwise remained healthy, 9 were examined at 19 to 31 months for persisting virus. In only one mink, small amounts were detected in the mesenteric lymph node and spleen nearly 28 months after inoculation. The other seven mink that survived the infection were not protected when challenged 31 months later with a small amount of the highly virulent Utah-1 strain. Even though still poorly understood, these varied responses of the royal pastel mink to infection with Aleutian disease virus of low virulence have important pathogenetic and epidemiological implications.     

Studies on pathogenesis of buffalo pox virus in rabbits: quantitative assay of virus in different organs

The buffalo pox virus was found to multiply in the skin, the primary site of inoculation with an eclipse phase of 12 hr. The virus was then detected in the skin after 15 hr followed by its appearance in regional lymph nodes 36 hr postinoculation. Primary viremia was detected 48 hr postinoculation, followed by detection of virus in the lungs, liver, and spleen. The virus multiplied in the lungs on day 4 and in the liver and spleen on day 5 postinoculation and its release led to secondary viremia. In a follow-up from day 7 to 14 postinoculation, the virus was detected in the kidneys, stomach, intestines, and gonads.     

Extraneural prion neuroinvasion without lymphoreticular system infection

While prion infection of the lymphoreticular system (LRS) is necessary for neuroinvasion in many prion diseases, in bovine spongiform encephalopathy and atypical cases of sheep scrapie there is evidence to challenge that LRS infection is required for neuroinvasion. Here we investigated the role of prion infection of LRS tissues in neuroinvasion following extraneural inoculation with the HY and DY strains of the transmissible mink encephalopathy (TME) agent. DY TME agent infectivity was not detected in spleen or lymph nodes following intraperitoneal inoculation and clinical disease was not observed following inoculation into the peritoneum or lymph nodes, or after oral ingestion. In contrast, inoculation of the HY TME agent by each of these peripheral routes resulted in replication in the spleen and lymph nodes and induced clinical disease. To clarify the role of the LRS in neuroinvasion, the HY and DY TME agents were also inoculated into the tongue because it is densely innervated and lesions on the tongue, which are common in ruminants, increase the susceptibility of hamsters to experimental prion disease. Following intratongue inoculation, the DY TME agent caused prion disease and was detected in both the tongue and brainstem nuclei that innervate the tongue, but the prion protein PrP(Sc) was not detected in the spleen or lymph nodes. These findings indicate that the DY TME agent can spread from the tongue to the brain along cranial nerves and neuroinvasion does not require agent replication in the LRS. These studies provide support for prion neuroinvasion from highly innervated peripheral tissues in the absence of LRS infection in natural prion diseases of livestock.     

Temporal distribution of transmissible mink encephalopathy virus in mink inoculated subcutaneously.

Information was sought on the temporal distribution of transmissible mink encephalopathy virus in royal pastel mink inoculated subcutaneously with 10(3.0) 50% intracerebral lethal doses of the Idaho strain. As determined by intracerebral assay in mink, extremely little replication of the virus occurred during the preclinical stage of infection. It seemed largely limited to lymph nodes draining the site of inoculation. Virus first appeared in the central nervous system (CNS) at 20 weeks, when all mink were still clinically normal. Early spongiform degeneration, limited to the posterior sigmoid gyrus of the frontal cortex, was first found at 28 weeks, or a few weeks before onset of clinical disease in most of the mink. Once virus reached the CNS, where greater concentrations occurred than elsewhere, it appeared in many extraneural sites (spleen, liver, kidney, intestine, mesenteric lymph node, and submandibular salivary gland). These seemingly anomalous findings, especially the limited extraneural replication of virus as a prelude to infection of the CNS, suggest that mink are not natural hosts of the virus. The results of this study support the generally held view that transmissible mink encephalopathy arises from chance or inadvertent infection of ranch mink with an exogenous virus, most likely feed-borne wild scrapie virus.     

Analysis of Aleutian disease virus infection in vitro and in vivo: demonstration of Aleutian disease virus DNA in tissues of infected mink.

Aleutian disease virus (ADV) infection was analyzed in vivo and in vitro to compare virus replication in cell culture and in mink. Initial experiments compared cultures of Crandell feline kidney (CRFK) cells infected with the avirulent ADV-G strain or the highly virulent Utah I ADV. The number of ADV-infected cells was estimated by calculating the percentage of cells displaying ADV antigen by immunofluorescence (IFA), and several parameters of infection were determined. Infected cells contained large quantities of viral DNA (more than 10(5) genomes per infected cell) as estimated by dot-blot DNA-DNA hybridization, and much of the viral DNA, when analyzed by Southern blot hybridization, was found to be of a 4.8-kilobase-pair duplex monomeric replicative form (DM DNA). Furthermore, the cultures contained 7 to 67 fluorescence-forming units (FFU) per infected cell, and the ADV genome per FFU ratio ranged between 2 X 10(3) and 164 X 10(3). Finally, the pattern of viral antigen detected by IFA was characteristically nuclear, although cytoplasmic fluorescence was often found in the same cells. Because no difference was noted between the two virus strains when cultures containing similar numbers of infected cells were compared, it seemed that both viruses behaved similarly in infected cell culture. These data were used as a basis for the analysis of infection of mink by virulent Utah I ADV. Ten days after infection, the highest levels of viral DNA were detected in spleen (373 genomes per cell), mesenteric lymph node (MLN; 750 genomes per cell), and liver (373 genomes per cell). In marked contrast to infected CRFK cells, the predominant species of ADV DNA in all tissues was single-stranded virion DNA; however, 4.8-kilobase-pair DM DNA was found in MLN and spleen. This observation suggested that MLN and spleen were sites of virus replication, but that the DNA found in liver reflected sequestration of virus produced elsewhere. A final set of experiments examined MLN taken from nine mink 10 days after Utah I ADV infection. All of the nodes contained ADV DNA (46 to 750 genomes per cell), and although single-stranded virion DNA was always the most abundant species, DM DNA was observed. All of the lymph nodes contained virus infectious for CRFK cells, but when the genome per FFU ratio was calculated, virus from the lymph nodes required almost 1,000 times more genomes to produce an FFU than did virus prepared from infected cell cultures.(ABSTRACT TRUNCATED AT 400 WORDS)     

Analysis of experimental mink enteritis virus infection in mink: in situ hybridization, serology, and histopathology.

Strand-specific hybridization probes were used in in situ hybridization studies to localize cells containing mink enteritis virus (MEV) virion DNA or MEV replicative-form DNA and mRNA. Following the experimental MEV infection of 3-month-old unvaccinated mink, a significant increase in serum antibodies to MEV was detected at postinfection day (PID) 6, 2 days after the onset of fecal shedding of virus. Prior to the appearance of virus in feces, viral DNA could be detected in the mesenteric lymph node and intestine. The largest percentage of cells positive for virion DNA was 10% and was detected in the intestine on PID 6. However, replication of the virus apparently peaked at PID 4. The number of MEV replicative-form DNA and mRNA molecules was found to be approximately 250,000 copies per infected lymph node cell or crypt epithelial cell. The localization, levels, and time course of viral replication have important implications for the pathogenesis of MEV-induced disease. The data presented on MEV are correlated with earlier results on the other mink parvovirus, Aleutian mink disease parvovirus, and a possible explanation for the remarkable differences in pathogenesis of disease caused by these two parvoviruses is discussed.     

Trafficking and Replication Patterns Reveal Splenic Macrophages as Major Targets of Dengue Virus in Mice

Human postmortem studies of natural dengue virus (DENV) infection have reported systemically distributed viral antigen. Although it is widely accepted that DENV infects mononuclear phagocytes, the sequence in which specific tissues and cell types are targeted remains uncharacterized. We previously reported that mice lacking alpha/beta and gamma interferon receptors permit high levels of DENV replication and show signs of systemic disease (T. R. Prestwood et al., J. Virol. 82:8411–8421, 2008). Here we demonstrate that within 6 h, DENV traffics to and replicates in both CD169⁺ and SIGN-R1⁺ macrophages of the splenic marginal zone or draining lymph node, respectively, following intravenous or intrafootpad inoculation. Subsequently, high levels of replication are detected in F4/80⁺ splenic red pulp macrophages and in the bone marrow, lymph nodes, and Peyer''s patches. Intravenously inoculated mice begin to succumb to dengue disease 72 h after infection, at which time viral replication occurs systemically, except in lymphoid tissues. In particular, high levels of replication occur in CD68⁺ macrophages of the kidneys, heart, thymus, and gastrointestinal tract. Over the course of infection, proportionately large quantities of DENV traffic to the liver and spleen. However, late during infection, viral trafficking to the spleen decreases, while trafficking to the liver, thymus, and kidneys increases. The present study demonstrates that macrophage populations, initially in the spleen and other lymphoid tissues and later in nonlymphoid tissues, are major targets of DENV infection in vivo.     

Derivation of neurotropic simian immunodeficiency virus from exclusively lymphocytetropic parental virus: pathogenesis of infection in macaques.

Neurological disease resulting from lentivirus (including human immunodeficiency virus) infections is usually caused by a strain of virus that replicates productively in microglia in vivo and in macrophage cultures in vitro. We undertook this study using the model of simian immunodeficiency virus in macaques (SIVmac) to test the hypothesis that macrophage tropism is a prerequisite for neurotropism of the virus. Using molecularly cloned SIVmac239, a virus which is lymphocyte- but not macrophagetropic, we showed that this virus failed to infect brain after intracerebral (i.c.) inoculation into two macaques. Rather, these inoculations resulted in disseminated infection in lymphoid organs and the bone marrow. Two sequential passages of infected bone marrow cells inoculated i.c. into new macaques resulted in severe neurological disease and classical neuropathological lesions. Virus obtained from affected brain answered the hypothetical question: it was neurotropic and macrophagetropic. New findings in the study were that both lymphocyte- and macrophage-tropic viruses were present in the animals, but the viruses localized in different tissues: the lymphotropic virus in the spleen, lymph nodes, and plasma and the macrophagetropic virus in the brain and lungs. To determine whether the brain virus was preferentially neurotropic and whether it had neuroinvasive properties, infectious brain homogenate was inoculated into one animal i.c. and into two others peripherally. The i.c. inoculated animal developed fatal encephalitis 5 months later, and examination of tissues showed cell-free virus only in brain homogenates. Only microglia were infected despite persistent viremia and infection in bone marrow cells. The two macaques inoculated peripherally remained healthy and were euthanized at 6 months. Virus replication was detected only in the bone marrow cells and peripheral blood mononuclear cells. No infection in any macrophage population in visceral organs was detected, and the virus did not invade the brain. The strictly microglial specificity of this virus suggested that different macrophage populations in the body may select specific phenotypes of lentivirus from the quasispecies of virus in the bone marrow. This could provide the basis for specific disease affecting different organ systems.     

Lassa virus infection in experimentally infected marmosets: liver pathology and immunophenotypic alterations in target tissues

Lassa virus causes thousands of deaths annually in western Africa and is considered a potential biological weapon. In an attempt to develop a small nonhuman primate model of Lassa fever, common marmosets were subcutaneously inoculated with Lassa virus strain Josiah. This inoculation resulted in a systemic disease with clinical and morphological features mirroring those in fatal human Lassa infection: fever, weight loss, high viremia and viral RNA load in tissues, elevated liver enzymes, and severe morbidity between days 15 and 20. The most prominent histopathology findings included multifocal hepatic necrosis with mild inflammation and hepatocyte proliferation, lymphoid depletion, and interstitial nephritis. Cellular aggregates in regions of hepatocellular necrosis were largely composed of HAM56-positive macrophages, devoid of CD3-positive and CD20-positive cells, and characterized by marked reductions in the intensity of HLA-DP, DQ, DR staining. A marked reduction in the major histocompatibility complex class II expression was also observed in the lymph nodes. Immunophenotypic alterations in spleen included reductions in overall numbers of CD20-positive and CD3-positive cells and the disruption of lymphoid follicular architecture. These findings identify the common marmoset as an appropriate model of human Lassa fever and present the first experimental evidence that replication of Lassa virus in tissues is associated with alterations that would be expected to impair adaptive immunity.     

Spread of herpes simplex virus in lymph nodes after experimental infection of mice

Herpes simplex virus was frequently isolated from ipsilateral popliteal lymph nodes after percutaneous inoculation of the dorsal face of the footpad, and from ipsi- and contralateral submandibular lymph nodes after percutaneous inoculation of the cheek or the orofacial area of mice. Virus was detected only on very rare occasion in nondraining lymph nodes (inguinal or axillary) or in contralateral popliteal lymph nodes, but was frequently isolated in contralateral lumbar lymph nodes after footpad inoculation. The presence of virus in lymph nodes paralleled or followed the invasion of ipsilateral sensory ganglia and was associated with dissemination of virus in contralateral sensory ganglia after unilateral inoculation. In older mice virus was detected only occasionally in lymph nodes and dissemination of virus in contralateral sensory ganglia was generally not observed. The results suggest that lymphatic spread may contribute to dissemination of virus in contralateral sensory ganglia after unilateral inoculation of mice.     

Resting CD4+ T lymphocytes but not thymocytes provide a latent viral reservoir in a simian immunodeficiency virus-Macaca nemestrina model of human immunodeficiency virus type 1-infected patients on highly active antiretroviral therapy

Despite suppression of viremia in patients on highly active antiretroviral therapy (HAART), human immunodeficiency virus type 1 persists in a latent reservoir in the resting memory CD4(+) T lymphocytes and possibly in other reservoirs. To better understand the mechanisms of viral persistence, we established a simian immunodeficiency virus (SIV)-macaque model to mimic the clinical situation of patients on suppressive HAART and developed assays to detect latently infected cells in the SIV-macaque system. In this model, treatment of SIV-infected pig-tailed macaques (Macaca nemestrina) with the combination of 9-R-(2-phosphonomethoxypropyl)adenine (PMPA; tenofovir) and beta-2',3'-dideoxy-3'-thia-5-fluorocytidine (FTC) suppressed the levels of plasma virus to below the limit of detection (100 copies of viral RNA per ml). In treated animals, levels of viremia remained close to or below the limit of detection for up to 6 months except for an isolated "blip" of detectable viremia in each animal. Latent virus was measured in blood, spleen, lymph nodes, and thymus by several different methods. Replication-competent virus was recovered after activation of a 99.5% pure population of resting CD4(+) T lymphocytes from a lymph node of a treated animal. Integrated SIV DNA was detected in resting CD4(+) T cells from spleen, peripheral blood, and various lymph nodes including those draining the gut, the head, and the limbs. In contrast to the wide distribution of latently infected cells in peripheral lymphoid tissues, neither replication-competent virus nor integrated SIV DNA was detected in thymocytes, suggesting that thymocytes are not a major reservoir for virus in pig-tailed macaques. The results provide the first evidence for a latent viral reservoir for SIV in macaques and the most extensive survey of the distribution of latently infected cells in the host.     

Temporal Analyses of Virus Replication, Immune Responses, and Efficacy in Rhesus Macaques Immunized with a Live, Attenuated Simian Immunodeficiency Virus Vaccine

Despite evidence that live, attenuated simian immunodeficiency virus (SIV) vaccines can elicit potent protection against pathogenic SIV infection, detailed information on the replication kinetics of attenuated SIV in vivo is lacking. In this study, we measured SIV RNA in the plasma of 16 adult rhesus macaques immunized with a live, attenuated strain of SIV (SIVmac239Δnef). To evaluate the relationship between replication of the vaccine virus and the onset of protection, four animals per group were challenged with pathogenic SIVmac251 at either 5, 10, 15, or 25 weeks after immunization. SIVmac239Δnef replicated efficiently in the immunized macaques in the first few weeks after inoculation. SIV RNA was detected in the plasma of all animals by day 7 after inoculation, and peak levels of viremia (10⁵ to 10⁷ RNA copies/ml) occurred by 7 to 12 days. Following challenge, SIVmac251 was detected in all of the four animals challenged at 5 weeks, in two of four challenged at 10 weeks, in none of four challenged at 15 weeks, and one of four challenged at 25 weeks. One animal immunized with SIVmac239Δnef and challenged at 10 weeks had evidence of disease progression in the absence of detectable SIVmac251. Although complete protection was not achieved at 5 weeks, a transient reduction in viremia (approximately 100-fold) occurred in the immunized macaques early after challenge compared to the nonimmunized controls. Two weeks after challenge, SIV RNA was also reduced in the lymph nodes of all immunized macaques compared with control animals. Taken together, these results indicate that host responses capable of reducing the viral load in plasma and lymph nodes were induced as early as 5 weeks after immunization with SIVmac239Δnef, while more potent protection developed between 10 and 15 weeks. In further experiments, we found that resistance to SIVmac251 infection did not correlate with the presence of antibodies to SIV gp130 and p27 antigens and was achieved in the absence of significant neutralizing activity against the primary SIVmac251 challenge stock.     

Rapid and Irreversible CD4+ T-Cell Depletion Induced by the Highly Pathogenic Simian/Human Immunodeficiency Virus SHIVDH12R Is Systemic and Synchronous

Highly pathogenic simian/human immunodeficiency virus chimeric viruses are known to induce a rapid, irreversible depletion of CD4+ T lymphocytes in the peripheral blood of acutely infected macaque monkeys. To more fully assess the systemic effects of this primary virus infection, specimens were collected serially between days 3 and 21 postinfection from variety of lymphoid tissues (lymph nodes, thymus, and spleen) and gastrointestinal tract and examined by DNA and RNA PCR, in situ hybridization, and immunohistochemical assays. In addition, the lymphoid tissues were evaluated by fluorescence-activated cell sorting. Virus infection was initially detected by DNA PCR on day 3 postinfection in lymph node samples and peaked on day 10 in the T-lymphocyte-rich areas of this tissue. CD4+ T-cell levels remained stable through day 10 in several lymphoid tissue specimens examined but fell precipitously between days 10 and 21. In situ terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays revealed the accumulation of apoptotic cells during the second week of infection in both lymph nodes and thymus, which colocalized, to a large extent, to sites of both virus replication and CD4+ T-lymphocyte loss.     

SIV-specific T lymphocyte responses in PBMC and lymphoid tissues of SIV-infected pigtailed macaques during suppressive combination antiretroviral therapy

There is currently no SIV macaque model in which the effects of combination antiretroviral therapy on tissue immune responses and latent reservoirs have been measured. This study was performed to define the impact of combination therapy on the specificity and distribution of the T lymphocyte response in multiple tissue compartments. Pigtailed macaques (Macaca nemestrina) were infected with SIV/17E-Fr and treated with combination antiretroviral therapy consisting of 9-R-(2-phosphonomethoxypropyl)adenine (PMPA) and beta-2',3'-dideoxy-3'-thia-5-fluorocytidine (FTC). The SIV-specific T lymphocyte response was measured in peripheral blood, spleen and several lymph nodes at necropsy by IFN-gamma Elispot analysis. Two animals (one treated, one untreated) had high acute peak viremia, which was associated with lower SIV-specific T lymphocyte responses in the peripheral blood and lymphoid tissues. In the treated animal, viremia was controlled to low or undetectable for the study duration, and virus-specific responses remained low. The untreated animal remained viremic throughout the study and developed clinical symptoms of AIDS. In contrast, the two animals that had lower acute peak viremia (one treated, one untreated) had more robust T lymphocyte responses, and controlled viral replication. Virus-specific responses were detected in the treated animal despite 6 months of suppressive therapy. These data suggest that in this model, in the context of acute peak viremia and weak T cell responses, combination therapy may be essential to control virus replication and disease progression. Conversely, in the setting of low initial viremia and robust T lymphocyte responses, treatment does not have a detrimental effect on the immune response.     

Heterogeneity of the simian immunodeficiency virus (SIV) specific CD8(+) T-cell response in mucosal tissues during SIV primary infection

Virus-specific CD8(+) T cells play an important role in controlling viral replication during acute primary infection. At this early stage, mucosal tissues represent a major site of viral replication. Therefore, the presence of functional virus-specific CD8(+) effector T cells in the mucosa during primary infection is a key issue in the pathogenesis of infection. In order to evaluate the extent of this response, six rhesus macaques were infected with simian immunodeficiency virus (SIV)mac251 and sacrificed on day 28 following infection. The functional activity of SIV-effector CD8(+) T cells was evaluated by means of a gamma-IFN ELISpot assay with autologous cells expressing SIV env, gag, pol and nef genes as antigen-presenting cells. This evaluation was performed on PBMCs, spleen, peripheral lymph node, gut-associated lymph node and lamina propria lymphocytes isolated from different mucosal sites. In parallel, the cell-associated viral load was quantified in all these tissues. Five macaques had gamma-IFN SIV-specific CD8(+) T cells in PBMCs and/or lymph nodes. However, in these macaques, these CD8(+) T cells were only present in seven mucosal sites out of 24 tested (the lamina propria lymphocytes of the duodenum, jejunum, ileum and colon were evaluated separately for each animal), whereas they were detected in all corresponding gut-associated lymph nodes. In addition, the mean frequency of SIV-specific gamma-IFN-secreting CD8(+) T cells was 117 +/- 228 per 10(6) cells in the lamina propria vs. 958 +/- 1184 in gut associated lymph nodes (P = 0.001). No overall correlation was observed between the CD8(+) T-cell activity and the viral load: among the 17 mucosal sites in which the virus was isolated, no specific activity was detected in 13 sites. In conclusion, these data indicate that the frequencies of SIV-specific gamma-IFN-secreting CD8(+) T cells are low in the mucosa during early primary infection. This may be of importance with regard to the intense viral replication observed in the mucosa at this stage.     

Characterization of chimeric full-length molecular clones of Aleutian mink disease parvovirus (ADV): identification of a determinant governing replication of ADV in cell culture.

The ADV-G strain of Aleutian mink disease parvovirus (ADV) is nonpathogenic for mink but replicates permissively in cell culture, whereas the ADV-Utah 1 strain is highly pathogenic for mink but replicates poorly in cell culture. In order to relate these phenotypic differences to primary genomic features, we constructed a series of chimeric plasmids between a full-length replication-competent molecular clone of ADV-G and subgenomic clones of ADV-Utah 1 representing map units (MU) 15 to 88. After transfection of the plasmids into cell culture and serial passage of cell lysates, we determined that substitution of several segments of the ADV-Utah 1 genome (MU 15 to 54 and 65 to 73) within an infectious ADV-G plasmid did not impair the ability of these constructs to yield infectious virus in vitro. Like ADV-G, the viruses derived from these replication-competent clones caused neither detectable viremia 10 days after inoculation nor any evidence of Aleutian disease in adult mink. On the other hand, other chimeric plasmids were incapable of yielding infectious virus and were therefore replication defective in vitro. The MU 54 to 65 EcoRI-EcoRV fragment of ADV-Utah 1 was the minimal segment capable of rendering ADV-G replication defective. Substitution of the ADV-G EcoRI-EcoRV fragment into a replication-defective clone restored replication competence, indicating that this 0.53-kb portion of the genome, wholly located within shared coding sequences for the capsid proteins VP1 and VP2, contained a determinant that governs replication in cell culture. When cultures of cells were studied 5 days after transfection with replication-defective clones, rescue of dimeric replicative form DNA and single-stranded progeny DNA could not be demonstrated. This defect could not be complemented by cotransfection with a replication-competent construction.     

仔猪人工感染猪繁殖与呼吸综合征病毒后宿主细胞凋亡动态变化规律的研究

28日龄长白仔猪滴鼻人工感染猪繁殖与呼吸综合征病毒(PRRSV),于接种后8h、24h、30h、3d、5d、7d、9d、11d、14d、21d、28d、35d和42d各随机剖杀2头,取各组织器官,利用原位末端标记(TdT-mediated dUTP nick end la-beling,TUNEL)法检测PRRSV感染仔猪后所产生的细胞凋亡情况。结果表明,PRRSV在体内可诱导肺脏、淋巴结(肺门淋巴结、肠系膜淋巴结、腹股沟淋巴结)、扁桃体、脾脏、肝脏、胰脏、十二指肠、胸腺、肾脏、子宫、睾丸、附睾、大脑和小脑等组织的细胞发生凋亡,发生凋亡的靶细胞主要是各种巨噬细胞、单核细胞以及生殖细胞。感染后8h即可检测到细胞凋亡,且凋亡细胞数目随着感染时间的延长在感染后第7d达到高峰,以后逐渐减少,至感染后42d时仍能检测到少量凋亡细胞。