Induction of an AIDS virus-related tuberculosis-like disease in macaques: a model of simian immunodeficiency virus- mycobacterium coinfection

Abstract

The mechanism by which human immunodeficiency virus (HIV)-Mycobacterium tuberculosis coinfection facilitates development of HIV-related tuberculosis is poorly characterized. Macaque models of simian immunodeficiency virus (SIV(mac))-Mycobacterium bovis BCG coinfection were employed to explore the pathogenesis of AIDS virus-related tuberculosis. Following BCG coinfection, SIV (SIV)-infected macaques with high viral loads developed an SIV-related tuberculosis-like disease. This disease was characterized clinically by a syndrome of diarrhea, anorexia, weight loss, and altered levels of consciousness and pathologically by the presence of disseminated granulomas. In contrast, SIV(mac)-infected macaques with low viral loads either showed no evidence of BCG-induced disease or developed focal granulomatous lesions. Pathogenic SIV-BCG interactions appeared to play a critical role in triggering the development of this SIV-related tuberculosis-like disease. BCG coinfection enhanced the destruction of CD4(+) T cells in SIV(mac)-infected macaques whose viral loads were high. Reciprocally, exacerbations of SIV disease led to marked suppression of BCG-specific T-cell responses, persistence of the BCG infection, and development of an SIV-related tuberculosis-like disease. Furthermore, development of this SIV-related tuberculosis-like disease was also seen in naïve macaques simultaneously inoculated with SIV(mac) and BCG. These results provide in vivo evidence that coinfection of AIDS virus-infected individuals with an avirulent mycobacterium can lead to development of a tuberculosis-like disease.

FIG. 1.

SIV_mac-infected macaques with high viral loads developed an SIV-related tuberculosis-like disease following BCG coinfection. Histological evaluation of SIV_mac-BCG-coinfected macaques with mycobacterial disease that were euthanatized revealed granulomas in the spleen, liver, and lung, and granulomatous inflammation was present in multiple organs. The specimens were collected when the animals were moribund or dead due to the terminal SIV_mac-BCG disease. The magnification of the liver section is higher than the magnification of the spleen and lung sections.

FIG. 2.

Accelerated SIV-induced disease following BCG coinfection contributed to development of the SIV-related tuberculosis-like disease in SIV_mac-infected macaques. Following BCG inoculation, the SIV_mac-infected macaques with high viral loads showed a mark increase in the level of plasma SIV RNA (A) and an accelerated decline in the number of CD4⁺ PBL (B), and they developed a fatal SIV-related tuberculosis-like disease. The plasma SIV RNA data in panel A were derived from QC-PCR and were verified by a branched DNA assay. The P values were <0.05 for the differences in plasma SIV RNA levels for the groups with and without the fatal BCG-associated disease; the P values were <0.01 for the different levels of CD4⁺ PBL in the groups with and without the fatal BCG-associated disease. For the macaques with high viral loads, the data obtained until the week when the animals developed the fatal SIV-related tuberculosis-like disease are shown. The symbols indicate means, and the error bars indicate standard errors of the means. The numbers of animals analyzed (n) are also indicated. TB, tuberculosis.

FIG. 3.

Persistent high levels of BCG detected in lymphoid cells of coinfected monkeys in association with the enhanced decline in CD4⁺ PBL counts. (A) BCG CFU quantitated by using lysates of 10⁶ cells from lymph nodes obtained from macaques after BCG coinfection. (B) Correlation between the enhanced decline in CD4⁺ PBL counts and persistence of viable BCG. The symbols indicate means, and the error bars indicate standard errors of the means. The numbers of animals analyzed (n) are also indicated. The P values were <0.01 for the differences in CFU in week 4 and thereafter for the groups with and without a fatal outcome. SIV^Hi, high SIV load; SIV^Lo, low SIV load; cont, control.

FIG. 4.

Inhibition of BCG-specific T-cell responses resulting from SIV-induced disease was associated with development of the SIV-related tuberculosis-like disease. The data are from proliferation assays in which we used PBL from coinfected macaques that exhibited an accelerated decline in CD4⁺ PBL counts and a tuberculosis-like disease (A and C), from macaques that did not exhibit accelerated depletion of CD4⁺ T cells or tuberculosis-like disease (B), and from controls that were not infected with SIV_mac (D). The SIV_mac-infected macaques whose data are shown in panel C and controls whose data are shown in panel D were inoculated twice with 10⁸ CFU of BCG. The macaques whose data are shown in panel B exhibited no evidence of a fatal tuberculosis-like disease and died from SIV-induced disease characterized by lymphoid depletion and other opportunistic infections. The symbols indicate means, and the error bars indicate standard errors of the means. The P values were <0.05 for the differences in proliferation indexes in week 8 and thereafter for the groups with and without a fatal outcome; the P values were <0.01 for the data obtained at any time for normal controls and the coinfected macaques with a fatal outcome. ConA, concanavalin A; BSA, bovine serum albumin; TB, tuberculosis.

FIG. 5.

Simultaneous SIV_mac-BCG coinfection of naïve macaques resulted in a profound decline in the number of CD4⁺ PBL (A and B) and suppression of BCG-specific T-cell responses (C and D). Plasma SIV RNA data were generated by a branched DNA assay. Data for the macaques infected with only SIV_mac are also shown in panels A and B. SIV_mac-infected macaques usually survive 2 to 5 years after infection. The proliferation assay was performed with CD4⁺ T-cell-enriched PBL from the SIV_mac-BCG-coinfected macaques. The symbols indicate means, and the error bars indicate standard errors of the means. The P values were <0.01 for the data obtained in weeks 4 and 6 for the controls (BCG only) and the macaques simultaneously coinfected with SIV_mac and BCG. ConA, concanavalin A; BSA, bovine serum albumin.

FIG. 6.

Suppression of T-cell proliferative responses to BCG coincided with the lack of clearance of BCG from lymphoid tissues of naïve macaques inoculated simultaneously with SIV_mac and BCG. BCG CFU were detected in the lymph nodes of the macaques after simultaneous inoculation with SIV_mac and BCG (A), and there was a correlation between persistent BCG infection and a marked decline in the number of CD4⁺ T cells (B) or suppressed T-cell proliferation (C). The symbols indicate means, and the error bars indicate standard errors of the means. The numbers of animals analyzed were the same as the numbers analyzed in the experiment whose results are shown in Fig. 5. The P values were <0.01 for the differences in BCG CFU in weeks 4 and 6 for the controls and the coinfected macaques.