Cell Tropism of Simian Immunodeficiency Virus in Culture Is Not Predictive of in Vivo Tropism or Pathogenesis

Abstract

SIVmac239/316 is a molecular clone derived from SIVmac239 that differs from the parental virus by nine amino acids in env. This virus, unlike the parental SIVmac239, is able to replicate well in alveolar macrophages in culture. We have not however, observed macrophage-associated inflammatory disease in any animal infected with SIVmac239/316. Therefore, we sought to examine the cell tropism of this virus in vivo in multiple tissues using in situ hybridization combined with immunohistochemistry and multilabel confocal microscopy for viral nucleic acid and multiple cell-type-specific markers for macrophages and T lymphocytes. Tissues examined included brain, heart, lung, lymph nodes, spleen, thymus, and small and large intestine. Matched tissues from macaques infected with the parental SIVmac239 and uninfected macaques were also examined. Many infected cells were detected in the tissues of animals infected with SIVmac239 and SIVmac239/316 although there appeared to be fewer positive cells in animals infected with SIVmac239/316. Surprisingly, in light of the cell culture observations, nearly every simian immunodeficiency virus-infected cell in animals inoculated with SIVmac239/316 was a T lymphocyte rather than a macrophage. This was true both during early infection (first 2 months) and in terminal disease. In contrast, as previously described, SIVmac239 was found in both T cells and macrophages in tissues as early as 21 days after infection. These studies indicate that during both acute and chronic SIVmac239/316 infection T lymphocytes rather than macrophages are the principal targets in vivo. These data combined with the absence of macrophageassociated lesions in SIVmac239/316-infected animals indicate that in vitro cell tropism is not predictive of in vivo tropism or disease pathogenesis.

Comparison of Plasma Viremia and Antibody Responses in Macaques Inoculated with Envelope Variants of Single-Cycle Simian Immunodeficiency Virus Differing in Infectivity and Cellular Tropism

“…Analysis of tissues revealed that more than 95% of the infected cells remaining in these animals were macrophages (28). Furthermore, plasma viral loads of nearly 10 6 RNA copy eq/ml were sustained in the presence of a reverse transcriptase (RT) inhibitor to block new rounds of infection (28). The half-life of infected naive and resting memory CD4 ϩ T cells may also be considerably longer than that of activated CD4 ϩ T cells that support high levels of virus replication.…”

Simian immunodeficiency virus selectively infects proliferating CD4+ T cells in neonatal rhesus macaques

“…After deparaffinization in xylene, rehydration in phosphate-buffered saline, and antigen retrieval with steam (citrate buffer), sections were incubated with anti-sense SIV riboprobes (Lofstrand Labs Ltd) encompassing essentially the entire SIV genome as previously described. 13 SIVmRNA ϩ cells were detected by the 2-hydroxy-3-napthoic acid-2 phenylanalide phosphate (HNPP) Fluorescent Detection Set (Roche Diagnostics Corporation; red). Furthermore, SIV-infected cells detected by this technique were also colabeled using unconjugated primary antibodies for BrdU and CD3 (both from DakoCytomation), and then with secondary antibodies conjugated to either Alexa 488 or Alexa 633 (Molecular Probes).…”

Elite Control, Gut CD4 T Cell Sparing, and Enhanced Mucosal T Cell Responses in Macaca nemestrina Infected by a Simian Immunodeficiency Virus Lacking a gp41 Trafficking Motif

“…2) and macrophages were not clearly infected, both animals developed chronic immune activation, as reflected in BrdU incorporation in CD4 ϩ and CD8 ϩ T cells and HLA-DR expression on CD8 ϩ T cells. These animals also developed thrombocytopenia, which is commonly associated with SIV disease progression in pig-tailed macaques (108), and tissues at necropsy showed pulmonary arteriopathy uniquely associated with SIV infection (56)(57)(58). Singlegenome amplification of the Env cytoplasmic domain in both animals showed conservation of the ⌬GY mutation, as well as R751G, which is a well-described mutation for the SIVmac239 clone (65).…”

“…S1B in the supplemental material). At necropsy, both had evidence of SIV infection, including generalized lymphoid hyperplasia and thrombocytopenia, pulmonary arteriopathy, and thrombosis (56)(57)(58), despite only slight reductions in numbers and percentages of CD4 ϩ T cells in blood and gut lamina propria (see below). In contrast, SIVmac239-infected animals exhibited findings typical of simian AIDS, with one or more of the following: meningoencephalitis with multinucleated giant cells, severe anemia and thrombocytopenia, giant cell pneumonia, esophageal candidiasis, and intranuclear inclusion bodies consistent with cytomegalovirus infection.…”