Nonpathogenesis of simian immunodeficiency virus infection is associated with reduced inflammation and recruitment of plasmacytoid dendritic cells to lymph nodes, not to lack of an interferon type I response, during the acute phase

Abstract

Divergent Toll-like receptor 7 (TLR7) and TLR9 signaling has been proposed to distinguish pathogenic from nonpathogenic simian immunodeficiency virus infection in primate models. We demonstrate here that increased expression of type I interferon in pathogenic rhesus macaques compared to nonpathogenic African green monkeys was associated with the recruitment of plasmacytoid dendritic cells in the lymph nodes and the presence of an inflammatory environment early after infection, instead of a difference in the TLR7/9 response.

FIG. 1.

Detection of IFNα1⁺ cells and productive SIV infection in LNs from RMs of Indian origin. (A) Detection of IFN-α1⁺ cells in LNs from one RM of Indian origin at 7, 11, 14, and 60 days after infection by in situ hybridization of (magnification, ×200). (B) Detection of virus-replicating cells (SIV RNA⁺ cells) in LNs at 7, 11, 14, and 60 days after infection by in situ hybridization of the same monkey as shown above (magnification, ×200).

FIG. 2.

Comparison of IFN-α1⁺ cells expression in pathogenic and nonpathogenic SIV models. (A) Dynamics of IFN-α1⁺ cells in LNs during primary SIV infection. IFN-α1-expressing cells (shown as IFN-α1⁺ cells/2 mm²) were detected by in situ hybridization at days 0, 7, 11, 14, and 60 in the LNs of Indian RMs, Chinese RMs (noncontrollers, NCs; controllers, Cs), AGMs, and Δnef SIV-infected RMs. IFN-α1⁺ cells were quantified, and means ± the standard deviations (SD) are shown. Statistical significance: *, P < 0.05; ns, not significant. (B) IFN-α1-expressing cells in LNs predict AIDS correlation between the number of IFN-α1⁺ cells at day 11 and survival (months of survival) and the extent of apoptosis quantified by the TUNEL method at day 14. Each symbol represents one individual. (C) Dynamics of productive SIV infection in LNs during primary SIV infection. Virus-replicating cells (shown as SIV⁺ cells/2 mm²) were detected by in situ hybridization in the LNs of Indian RMs, Chinese RMs (noncontrollers, NCs; controllers, Cs), AGMs, and Δnef SIV-infected RMs at 7, 11, 14, and 60 days after SIVmac251 infection. SIV-RNA⁺ cells were quantified, and means ± the SD are shown. Statistical significances: *, P < 0.05; ns, not significant.

FIG. 3.

Detection of type I IFN in the blood of SIV-infected monkeys. Type I IFN-α was assessed by ELISA. Each symbol represent an individual monkey. Statistical significance: *, P < 0.05; ns, not significant.

FIG. 4.

IFN-α production after TLRs stimulation. (A) PBMC isolated from healthy monkeys were stimulated overnight in the absence (Med) or presence of the TLR agonists: LPS, 10 ng/ml (TLR4); CLO97, 1 μg/ml (TLR7); and CpG-DNA, 1 μM (TLR9). Supernatants were collected and assessed for the detection of type I IFN-α by ELISA. Values are means ± the SD (n = 7). (B) Phenotype of IFN-α2a-expressing cells by flow cytometry. PBMC isolated from monkeys (RM versus AGM) were stimulated overnight in the absence (Med) or presence of CLO97 at 1 μg/ml (TLR7). Cells were stained with antibodies directed against IFN-α2a, CD11c, and CD123 and included a lineage marker (Lin⁺). The gating strategy is shown. Similar data have been obtained with four healthy monkeys of each species.

FIG. 5.

Dynamics of pDCs in LNs during primary SIV infection. (A) Gating strategy used to analyze pDCs in LNs as defined by Lin⁻ CD123⁺ HLA-DR⁺ cells. (B) The results for one representative RM analyzed at different time points after infection are shown. (C) pDCs were defined as Lin⁻ CD123⁺ HLA-DR⁺ cells and analyzed by flow cytometry. Means ± the SD are shown in NC-RMs (NCs, n = 6) and C-RMs (Cs, n = 6), SIVΔnef-infected RMs (n = 6), and SIV-infected AGMs (n = 6). Statistical significance: *, P < 0.05; ns, not significant.

FIG. 6.

Dynamics of IL-8 during primary SIV-infection. (A) Viral load was quantified in peripheral blood of SIV-infected Indian RMs, Chinese NC- and C-RMs, SIV-infected AGMs, and SIVΔnef-infected RMs at different days postinfection. (B) The levels of IL-8 were detected in the sera by ELISA at days 0, 7, 14, 21, 30, and 60 after inoculation. Values are means ± the SD (n = 6). (C) IL-8 production after TLRs stimulation. PBMC isolated from healthy monkeys (solid ovals, Indian RMs; open ovals, Chinese RMs; solid diamonds, AGMs [n = 7]) were stimulated overnight in the absence (Med) or presence of the following TLR agonists: LPS, 10 ng/ml (TLR4); CLO97, 1 μg/ml (TLR7); and CpG-DNA, 1 μM (TLR9). Supernatants were collected and assessed for the detection of IL-8 by ELISA. Each symbol represents one individual.