Immunoglobulin-A nephropathy with crescentic glomerulonephritis in a pigtailed macaque (Macaca nemestrina).

A 4-year-old female pigtailed macaque (Macaca nemestrina), experimentally coinfected with simian immunodeficiency virus (SIVmac251) and Mycobacterium bovis(bacillus Calmette-Guerin), was euthanatized 1 year after infection because of weight loss and labored breathing. On gross examination, both kidneys were found to be markedly enlarged (right: 54.7 g and left: 51.7 g; normal < 20 g). Renal lesions were evaluated by histopathologic, immunohistochemical, and ultrastructural methods. Light microscopy revealed that the glomeruli were diffusely hypercellular with expansion of the mesangial matrix, and crescent formation affected approximately 60% of the glomeruli. By immunohistochemical evaluation, it was found that the crescents were composed principally of macrophages, as seen by CD68 (KP1), MRP8, MAC387, and HAM56 expression. Electron microscopic examination of the glomeruli revealed extensive intramembranous, subendothelial, and mesangial electron-dense deposits and multifocal fusion of the visceral epithelial foot processes. Immunofluorescence, used to determine the composition of the electron-dense deposits, revealed diffuse granular mesangial and capillary staining for immunoglobulin A (IgA). The renal changes described in this case report are most consistent with the findings of crescentic gloerulonephritis with IgA immune complex deposition in the glomerular basement membrane and mesangium as described in humans with IgA nephropathy.

Expression of peripherin in the brain of macaques (Macaca mulatta and Macaca fascicularis) occurs in astrocytes rather than neurones and is associated with encephalitis.

Peripherin is a member of the type III intermediate filament family, expressed in neurones of the peripheral nervous system of many species and in a discrete subpopulation of neurones of the central nervous system (CNS) during early development in rodents. Previous studies on rats have shown that peripherin immunoreactivity increased significantly in cell bodies of spinal motor neurones following axonal injury. Our study examined the expression of peripherin in the cerebrum of normal macaques (Macaca mulatta and Macaca fascicularis) and those with encephalitis of viral (simian immunodeficiency virus and simian virus 40) or autoimmune (experimental allergic encephalomyelitis) aetiology. Immunohistochemistry, immunoelectronmicroscopy, immunofluorescence and confocal microscopy were performed on tissue sections using antibodies against cell-specific markers and peripherin. Peripherin-positive cells were absent in the cerebrum of normal macaques of all ages examined, whereas animals with encephalitis had peripherin-positive cells associated with inflammatory infiltrates. Further evaluation revealed that these peripherin-positive cells were not neurones, but were predominantly astrocytes expressing glial fibrillary acidic protein. Our study suggests that peripherin is not neurone-specific in the CNS of macaques; peripherin is expressed in astrocytes of animals with encephalitis.

Association of simian virus 40 with a central nervous system lesion distinct from progressive multifocal leukoencephalopathy in macaques with AIDS.

The primate polyomavirus SV40 is known to cause interstitial nephritis in primary infections and progressive multifocal leukoencephalopathy (PML) upon reactivation of a latent infection in SIV-infected macaques. We now describe a second central nervous system manifestation of SV40: a meningoencephalitis affecting cerebral gray matter, without demyelination, distinct from PML. Meningoencephalitis appears also to be a primary manifestation of SV40 infection and can be seen in conjunction with SV40-induced interstitial nephritis and pneumonitis. The difference in the lesions of meningoencephalitis and PML does not appear to be due to cellular tropism, as both oligodendrocytes and astrocytes are infected in PML and meningoencephalitis, as determined by in situ hybridization or immunohistochemistry for SV40 coupled with immunohistochemistry for cellular determinants. This is further supported by examination of SV40 nucleic acid sequences from the ori-enhancer and large-T-antigen regions, which reveals no tissue-or lesion-specific variation in SV40 sequences.

Gastrointestinal tract as a major site of CD4+ T cell depletion and viral replication in SIV infection.

Human and simian immunodeficiency virus (HIV and SIV) replicate optimally in activated memory CD4(+) T cells, a cell type that is abundant in the intestine. SIV infection of rhesus monkeys resulted in profound and selective depletion of CD4+ T cells in the intestine within days of infection, before any such changes in peripheral lymphoid tissues. The loss of CD4+ T cells in the intestine occurred coincident with productive infection of large numbers of mononuclear cells at this site. The intestine appears to be a major target for SIV replication and the major site of CD4+ T cell loss in early SIV infection.

Characterization of gut-associated lymphoid tissue (GALT) of normal rhesus macaques.

This study characterizes the gut-associated lymphoid tissue (GALT) of normal healthy rhesus macaques and compares the percentages of T and B cell subsets to those of systemic lymphoid tissue. Lymphocytes from the systemic lymphoid tissue (spleen, axillary, and inguinal lymph nodes), mesenteric lymph nodes (MLN), and intestinal epithelium (IEL) and lamina propria (LPL) of the jejunum, ileum, and colon were examined from both adult and juvenile, normal rhesus macaques. Lymphocytes were analyzed for expression of CD2, CD3, CD4, CD8, CD25, gamma delta TCR, and CD20 by two- or three-color flow cytometric analysis. Sections of jejunum, ileum, and colon were examined for CD3, CD20, and CD103 expression by immunohistochemistry. Peyer's patches were also examined for CD3, CD4, CD8, and CD20 expression by immunohistochemistry. Most IEL and LPL were CD103+, CD3+ T cells with significantly fewer CD20+ B cells. The IEL were predominantly CD3+CD8+ (63-80%), with very few CD4+ cells, whereas CD4:CD8 ratios in the LPL ranged from 0.74 to 1.3. Three to 38% of the IEL were gamma delta TCR positive, but gamma delta expression was rare in the LPL and MLN. gamma delta TCR expression was also higher in the IEL of younger animals. LPL had higher expression of CD25 compared to IEL and systemic tissues, particularly in aged animals. CD4+CD8+, double-positive and CD3+CD4-CD8- double-negative cells were also observed in GALT. These results demonstrate that GALT of rhesus macaques is remarkably similar to that of humans, further justifying the use of these animals as models for various intestinal disorders.

Neuroinvasion by simian immunodeficiency virus coincides with increased numbers of perivascular macrophages/microglia and intrathecal immune activation.

During peak viremia and initial antibody response, rhesus macaques infected with pathogenic and nonpathogenic isolates of SIV show distinct differences in viral load and tissue distribution. Animals infected with pathogenic isolates of SIV invariably have virus in the CSF and brain parenchyma by two weeks postinoculation, whereas animals infected with nonpathogenic isolates do not. Mechanisms underlying neuroinvasion by SIV and HIV are unknown, but recruitment of latently infected mononuclear cells from the peripheral circulation (Trojan horse theory) is frequently proposed. Circulating monocytes, from which perivascular macrophage/microglia are derived, are a likely vehicle for cell-associated transport of virus across the blood-brain barrier. This transport and the kinetics of perivascular macrophage/microglial turnover in the CNS likely depend on endothelial and leukocyte adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), which has previously been shown to be upregulated on cerebrovascular endothelium in SIV encephalitis. To investigate the role of peripheral monocyte recruitment into the perivascular macrophage/microglial cell pool at the time of initial viral neuroinvasion, we examined the temporal relationships among perivascular macrophage/microglia density, endothelial VCAM-1 expression and localization of viral nucleic acid in the CNS of macaques acutely infected with pathogenic and nonpathogenic molecular clones of SIV. The concentration of CSF quinolinic acid, a marker of intrathecal immune and macrophage activation, was examined concurrently. We found that significant increases in the density of perivascular macrophages/microglia coincided with viral neuroinvasion and marked elevations in CSF quinolinic acid. Furthermore, combined in situ hybridization and immunohistochemistry demonstrated that infected perivascular cells were macrophages/microglia. These findings provide evidence suggesting that neuroinvasion occurs through an influx of infected monocytes which take up residence in the CNS as perivascular macrophages/microglia. VCAM-1 expression, however, was not clearly correlated with these events, thus its contribution to initial viral neuroinvasion is unclear.

Chemokine expression in simian immunodeficiency virus-induced AIDS encephalitis.

The pathogenesis of neurological dysfunction associated with human immunodeficiency (HIV)-1 infection is uncertain. However, the presence of macrophage infiltrates in the central nervous system is a key feature of HIV encephalitis and is correlated with HIV-associated dementia. Moreover, it has been demonstrated that HIV-infected monocyte/macrophages can produce toxic substances that may play a critical role in the development of HIV-associated dementia. However, the exact mechanisms responsible for HIV infection and leukocyte recruitment to the central nervous system remain speculative. Similar to HIV-infected patients, simian immunodeficiency virus (SIV)-infected macaque monkeys develop immunosuppression and acquired immune deficiency syndrome (AIDS)-related inflammatory disorders, including AIDS encephalitis. In this study, we demonstrate that encephalitic brain from SIV-infected animals has elevated immunohistochemical expression of the C-C chemokines, macrophage inflammatory protein-1 alpha and -beta, RANTES, and monocyte chemotactic protein-3, and the C-X-C chemokine interferon-inducible protein-10. These findings suggest that one or all of of these chemokines could be involved in leukocyte recruitment to the brain in SIV-infected macaque monkeys.

A case of pulmonary cestodiasis in a simian immunodeficiency virus-infected pigtailed macaque (Macaca nemestrina) in which virus-infected leukocytes are present within the lesion.

The larvae of Mesocestoides are rarely encountered in nonhuman primates, with most cases reported in baboons. Infection of macaques has been occasionally diagnosed, but Mesocestoides in the lung parenchyma is extremely rare. We have previously demonstrated that in macaques with terminal AIDS, simian immunodeficiency virus (SIV)-infected leukocytes are rarely found in cellular infiltrates associated with opportunistic infections or preexisting disease. Here we describe larvae (tetrathyridia) of the cestode Mesocestoides in the lung of an adult, pigtailed macaque (Macaca nemestrina) during acute SIV infection in which virus-positive cells are present within the cellular infiltrates. These results describe a rare parasitic disease in pigtailed macaques and demonstrate that lentivirus-infected leukocytes can be associated with inflammatory sites during acute infection.

Induction of lymphocyte proliferation and severe gastrointestinal disease in macaques by a nef gene variant SIVmac239.

The molecularly cloned virus known as SIVmac239/YEnef causes extensive lymphocyte activation in unstimulated peripheral mononuclear cell cultures and induces an acute disease syndrome in macaque monkeys. Here we describe the histopathological and immunophenotypic changes and viral localization in peripheral lymph nodes, spleen, and gastrointestinal tract (including the gut-associated lymphoid tissue (GALT) in rhesus monkeys inoculated with SIVmac239/YEnet beginning at day 3 postinoculation (pi). The findings are compared with those of rhesus monkeys inoculated with the same dose of parental SIVmac239. Histopathological examination of peripheral lymphoid tissue and GALT demonstrated marked hyperplasia of T-cell-dependent regions and involution of germinal centers as early as day 7 pi. The most striking lesions were multifocal areas of lymphohistiocytic gastroenteritis and colitis. Cellular infiltrates peaked between day 7 and 14 pi and were composed primarily of CD3+ T lymphocytes and HAM-56+ monocyte/macrophages. Many of these inflammatory cells were also strongly immunoreactive for teh nuclear proliferation antigen Ki-67. Despite the presence of severe gastrointestinal pathology by day 7 pi, no significant difference in the numbers of virus-positive cells in the gastrointestinal tract was observed between these animals and SIVmac239-infected animals examined at the same time point. However, the distribution of virus in the gastrointestinal tract was markedly different, with virus localized to lymphoid nodules of GALT in SIVmac239-infected animals and restricted to areas of lymphohistiocytic gastroenteritis and colitis in animals infected with SIVmac239/YEnef. Our data indicate that the acute disease syndrome induced by SIVmac239/YEnef is not simply related to increased viral replication in the gastrointestinal tract but is likely due to inappropriate virus-induced T lymphocyte activation and proliferation in GALT and subsequent mucosal destruction.

Evaluation of anti-human antibodies for immunohistochemistry on archival nonhuman primate tissues.

A panel of commercially available antibodies which recognize specific antigens on human tissues was developed for use in immunohistochemistry on tissues from eight species of nonhuman primates. Antibodies were selected for potential usefulness in diagnostic pathology, and for effectiveness in formalin-fixed, paraffin-embedded tissues. Tissues from four species of macaques and four New World monkeys were evaluated. Using these antibodies we were able to identify 17/21 antigens examined in all eight species, and 21/21 antigens in the four species of macaques. Detailed immunohistochemistry protocols are presented, along with a systematic approach to developing a protocol for a new antibody.

A spontaneous squamous cell carcinoma of the oral cavity in a squirrel monkey (Saimiri sciureus)

A spontaneous squamous cell carcinoma was diagnosed in the oral cavity of an adult female squirrel monkey (Saimiri sciureus). Immunohistochemical analysis of the neoplasm demonstrated cytokeratin and vimentin, but not S100 or desmin in the neoplastic epithelial cells.

Arteriopathy in macaques infected with simian immunodeficiency virus.

BACKGROUND: An arteriopathy characterized by intimal and medial thickening and fibrosis was seen in 19 of 85 rhesus monkeys infected with simian immunodeficiency virus (SIV), a lentivirus with morphologic, genetic, and biologic similarities to HIV-1 and HIV-2. EXPERIMENTAL DESIGN: All cases of simian AIDS in rhesus monkeys at the New England Regional Primate Research Center, resulting from either experimental or naturally acquired SIV infection, were retrospectively examined for evidence of histopathologic changes to the vasculature. Of the 85 SIV-related deaths recorded in the pathology files to date, tissues from 19 animals were chosen for further study because of thickening, disruption, inflammation, or other abnormality to any layer of the vascular wall. The lesion was characterized by special stains, immunoperoxidase procedures, and ultrastructural examination. RESULTS: Affected monkeys of both sexes varied in age from 4 months to 17 years at the time of inoculation and survived from 41 days to 4 years after infection. Pulmonary arteries were affected in all 19 animals, while vessels in other parenchymal organs were involved less frequently. In addition to sometimes marked intimal thickening with luminal occlusion, the internal elastic laminae were fragmented and interrupted. Seven of 19 animals had pulmonary thromboses with varying degrees of organization and recanalization. Immunohistochemical studies, special stains, and ultrastructural analyses revealed the thickened intimae to be composed predominantly of collagen, extracellular matrix, and smooth muscle cells. Ultrastructurally, endothelial cells from both early (no intimal thickening) and advanced lesions were plump, vacuolated, and often disorganized and detached from the subendothelial space. Increased numbers of macrophages (CD68+) were found in the adventitia and occasionally in the thickened intima and media. Rare, fully differentiated macrophages (CD68+, 25F9+) were demonstrated in lumina of affected vessels, some of which expressed p27 SIV gag protein. However, the lesion was not uniformly associated with localization of either viral protein or RNA at the site using immunohistochemistry or in situ hybridization, respectively. A similar arterial lesion has been described in children with AIDS. CONCLUSIONS: The morphologic findings in macaques and their similarity to arteriosclerotic changes induced by experimental endothelial damage in other species collectively suggest that arteriopathy in AIDS may represent a manifestation secondary to primary endothelial injury.

Simian virus 40-induced disease in rhesus monkeys with simian acquired immunodeficiency syndrome.

Simian virus 40 (SV40) disease was diagnosed in four rhesus monkeys that died with SIV-induced acquired immunodeficiency syndrome (AIDS). One juvenile monkey seroconverted for SV40 6 months after inoculation with SIV and developed severe bilateral tubulointerstitial nephritis. In contrast, progressive multifocal leukoencephalopathy (PML) occurred in two adult monkeys that were seropositive for SV40 before SIV inoculation, as well as a third adult that was naturally infected with SIV and seropositive for SV40 5 years before death. Large intranuclear inclusions containing abundant polyomavirus particles were limited to either renal tubular epithelial cells or oligodendrocytes. In situ DNA hybridization for SV40 large T antigen further demonstrated that SV40 nucleic acid was localized to either kidney or brain tissue. By immunohistochemical analysis, areas of central nervous system inflammation and demyelination were shown to contain CD68+ macrophages (gitter cells), aggregates of CD8+ T lymphocytes, and numerous gemistocytic astrocytes that labeled for glial fibrillary acidic protein. These observations indicate that rhesus monkeys with SIV-induced AIDS are predisposed to polyomaviral disease, in which SV40 nucleic acid is observed in renal tissue in primary infections and brain tissue after viral reactivation. Furthermore, this organ-specific replication suggests that tissue-tropic strains of SV40 may develop in immunodeficient monkeys.