Specific pathogen-free status alters immunophenotype in rhesus macaques: implications for the study of simian immunodeficiency virus.

The repertoire of viruses to which research primates are exposed, even in the absence of clinical disease, may contribute to experimental confounding. In this study we examined whether standard specific pathogen-free (SPF) rhesus macaques exposed to a wider spectrum of enzootic viruses and expanded SPF macaques derived to exclude a greater number of viral agents would display alterations in immune activation or immune cell populations. Given the impact of immunophenotype on human immunodeficiency virus (HIV) progression and the importance of the simian immunodeficiency virus (SIV) model for the study of HIV pathogenesis, we elected to additionally examine the impact of SPF status on the capacity of peripheral blood mononuclear cells (PBMCs) to support SIV replication. The expanded SPF group displayed significant immune alterations including increased serum interleukin (IL)-15 and a greater in vitro elaboration of GM-CSF, IL1ra, VEGF, IL-10, IL12/23, and MIP-1b. Consistent with reduced viral antigenic exposure in expanded SPF macaques, decreased CD4(+) and CD8(+) transitional and effector memory (T(EM)) cell populations were observed. Expanded SPF PBMC cultures also demonstrated an increased peak (192.61 ng/ml p27) and area under the curve in in vitro SIV production (1968.64 ng/ml p27) when compared to standard SPF macaques (99.32 ng/ml p27; p=0.03 and 915.17 ng/ml p27; p=0.03, respectively). In vitro SIV replication did not correlate with CD4(+) T(EM) cell counts but was highly correlated with serum IL-15 in the subset of animals examined. Findings suggest that an altered immunophenotype associated with the maintenance of primates under differing levels of bioexclusion has the potential to impact the outcome of SIV studies and models for which the measurement of immunologic endpoints is critical.

Naturally occurring Tyzzer's disease in cotton-top tamarins (Saguinus oedipus).

We noted naturally occurring infection with Clostridium piliforme (Tyzzer's disease) in 2 captive-reared cotton-top tamarins (Saguinus oedipus). Spontaneous Tyzzer's disease has been reported in multiple species of laboratory, domestic, and wild animals but is extremely rare in humans and nonhuman primates. Distinct from idiopathic colitis, which is common in cotton-top tamarins, these 2 tamarins had severe, transmural, necrotizing typhlocolitis accompanied by myocarditis and hepatitis. Abundant bacteria compatible with C. piliforme, the etiologic agent of Tyzzer's disease, were present adjacent to lesions in the cecum-colon, liver, and heart. Therefore, colitis caused by C. piliforme, although rare, should be included as a differential diagnosis in cotton-top tamarins and as a cause of postnatal mortality in this species.

GB virus B infection of the common marmoset (Callithrix jacchus) and associated liver pathology.

GB virus B (GBV-B) is a flavivirus that is related closely to hepatitis C virus (HCV) and induces an acute hepatitis when inoculated into several species of New World primates. Common marmosets (Callithrix jacchus) are a widely available, non-endangered primate species that is susceptible to GBV-B infection and develops a characteristic acute hepatitis. Here, animals were found to be susceptible to serially passaged serum and GBV-B transcripts. Hepatic pathology and peripheral viraemia could be quantified biochemically, immunophenotypically and morphologically, and persisted for periods of up to 6 months in some animals. Hepatitis was characterized by a marked influx of CD3+ CD8+ T lymphocytes and CD20+ B cells within the first 2 months of primary infection. The results of this study document the marmoset as another small, non-human primate species in which the pathogenesis of GBV-B can be studied and used as a surrogate model of HCV infection for investigation of pathogenesis and antiviral drug development.

Alterations in expression of monocyte chemotactic protein-1 in the simian immunodeficiency virus model of disseminated Mycobacterium avium complex.

Mycobacterium avium complex (MAC) infection is the most common disseminated bacterial infection in untreated patients with acquired immunodeficiency syndrome (AIDS). We investigated the potential role of monocyte chemotactic protein-1 (MCP-1) in the pathogenesis of disseminated MAC, using the simian immunodeficiency virus (SIV)/macaque model of AIDS. Macaques were inoculated with SIV, followed by challenge with a pathogenic AIDS isolate of M. avium 14 days later. After challenge with M. avium, marked increases in serum MCP-1 levels were detected in SIV-infected macaques, a finding that was duplicated in coinoculated bronchoalveolar macrophages. MCP-1 levels were significantly higher in SIV-infected macaques than in non-SIV-infected controls (327.1 vs. 151.5 pg/mL, respectively; P=.04), suggesting that up-regulation of MCP-1 contributes to the development of progressive mycobacterial disease. Similarly, morphometric analysis revealed increased expression of MCP-1 in hepatic microgranulomas from SIV-infected macaques. We conclude that the pronounced increases in MCP-1 levels demonstrated in tissue and serum samples after M. avium inoculation may play a role in the development of disseminated mycobacterial disease.

Mucosal priming of simian immunodeficiency virus-specific cytotoxic T-lymphocyte responses in rhesus macaques by the Salmonella type III secretion antigen delivery system.

Nearly all human immunodeficiency virus (HIV) infections are acquired mucosally, and the gut-associated lymphoid tissues are important sites for early virus replication. Thus, vaccine strategies designed to prime virus-specific cytotoxic T lymphocyte (CTL) responses that home to mucosal compartments may be particularly effective at preventing or containing HIV infection. The Salmonella type III secretion system has been shown to be an effective approach for stimulating mucosal CTL responses in mice. We therefore tested DeltaphoP-phoQ attenuated strains of Salmonella enterica serovar Typhimurium and S. enterica serovar Typhi expressing fragments of the simian immunodeficiency virus (SIV) Gag protein fused to the type III-secreted SopE protein for the ability to prime virus-specific CTL responses in rhesus macaques. Mamu-A*01(+) macaques were inoculated with three oral doses of recombinant Salmonella, followed by a peripheral boost with modified vaccinia virus Ankara expressing SIV Gag (MVA Gag). Transient low-level CTL responses to the Mamu-A*01 Gag(181-189) epitope were detected following each dose of Salmonella. After boosting with MVA Gag, strong Gag-specific CTL responses were consistently detected, and tetramer staining revealed the expansion of Gag(181-189)-specific CD8(+) T-cell responses in peripheral blood. A significant percentage of the Gag(181-189)-specific T-cell population in each animal also expressed the intestinal homing receptor alpha4beta7. Additionally, Gag(181-189)-specific CD8(+) T cells were detected in lymphocytes isolated from the colon. Yet, despite these responses, Salmonella-primed/MVA-boosted animals did not exhibit improved control of virus replication following a rectal challenge with SIVmac239. Nevertheless, this study demonstrates the potential of mucosal priming by the Salmonella type III secretion system to direct SIV-specific cellular immune responses to the gastrointestinal mucosa in a primate model.