Persistence and dissemination of simian retrovirus type 2 DNA in relation to viremia, seroresponse, and experimental transmissibility in Macaca fascicularis

Abstract

Endemic simian retrovirus (SRV) infection can cause fatal simian AIDS in Macaca fascicularis, but many individuals survive with few clinical signs. To further clarify the parameters of SRV pathogenesis, we investigated the persistence of viral DNA forms in relation to active viremia, antibody response, and transmissibility of infection. In M. fascicularis from endemically SRV-2-infected colonies, viral DNA was present in both linear and unintegrated long terminal repeat circular forms in peripheral blood mononuclear cells of all viremic and many nonviremic animals. Long-term followup of three individuals with distinct infection patterns demonstrated persistence of linear and circular forms of viral DNA in peripheral blood mononuclear cells and tissues, irrespective of viremia or antibody status, but reactivation of latent infections was not observed. The role of viral DNA in transmission and early pathogenesis of SRV-2 was investigated by inoculation of SRV-2 DNA-positive blood into groups of naïve M. fascicularis from either a viremic or nonviremic donor and subsequent analysis of the virological and serological status of the recipients. Transmission of SRV and development of anti-SRV antibodies were only observed in recipients of blood from the viremic donor; transfer of SRV provirus and unintegrated circular DNA in blood from the nonviremic donor did not lead to infection of the recipients. These results indicate that a proportion of M. fascicularis are able to effectively control the replication and infectivity of SRV despite long-term persistence of viral DNA forms in infected lymphocytes.

FIG. 1.

Analysis of SRV-specific PCR products by Southern hybridization. Samples were analyzed by both (A) LTR assay (277-bp product) and (B) one-LTR circle assay (449-bp product). Samples were: H₂O (lanes 1 and 2), extraction control (lane 3), DNA extracted from Raji cells infected with SRV-1 (lane 4) or SRV-2 (lane 5), uninfected Raji cell control (lane 6), extraction control (lane 7), DNA extracted from Raji cells infected with SRV-4 (lane 8) or SRV-5 (lane 9), extraction control (lane 10), DNA extracted from Raji cells infected with SRV-3 (lane 11), DNA from uninfected macaque PBMCs (lanes 12 to 23), extraction control (lane 24), DNA from infected macaque PBMCs (lane 25), H₂O (lane 26).

FIG. 2.

Analysis of serum anti-SRV antibodies by ELISA. 977G viral lysate was used as the antigen substrate. ELISAs were performed in duplicate, and the graphs shown are representative. A log₁₀ endpoint titer of >1.5 was considered a positive result; the cutoff is indicated by the dashed line. (A) Sequential analysis of anti-SRV antibodies in three animals, (▪) 540FC, (▵) 963DBDA, and (♦) 977G. (B) Analysis of recipient anti-SRV antibodies. Group A recipients of blood from 977G: (♦) X382, □ X383. Group B recipients of blood from 540FC: (▵) X384, (▪) X385.

FIG. 3.

Western blot analysis of plasma anti-SRV antibody reactivity. Proteins within the lysates prepared from Raji cells infected with the 977G SRV isolate or uninfected Raji cells were separated by SDS-PAGE and analyzed by Western blotting with the following plasma samples: X382 day −21 prebleed (lane 1), X382 day 109 postinoculation (lane 2), X383 day −21 prebleed (lane 3), X383 day 109 postinoculation (lane 4), 977G day 168 (lane 5), and 540FC day 168 (lane 6). Viral proteins were detected by plasma antibody reactivity at 70 kDa and between 20 kDa and 35 kDa. A low level of reactivity towards uninfected Raji cell components was detected at approximately 60 kDa.