Reactivation of latent tuberculosis in rhesus macaques by coinfection with simian immunodeficiency virus

Abstract

Background: Tuberculosis (TB) and AIDS together present a devastating public health challenge. Over 3 million deaths every year are attributed to these twin epidemics. Annually, ∼11 million people are coinfected with HIV and Mycobacterium tuberculosis (Mtb). AIDS is thought to alter the spontaneous rate of latent TB reactivation.

Methodology: Macaques are excellent models of both TB and AIDS. Therefore, it is conceivable that they can also be used to model coinfection. Using clinical, pathological, and microbiological data, we addressed whether latent TB infection in rhesus macaques can be reactivated by infection with simian immunodeficiency virus (SIV).

Results: A low-dose aerosol infection of rhesus macaques with Mtb caused latent, asymptomatic TB infection. Infection of macaques exhibiting latent TB with a rhesus-specific strain of SIV significantly reactivated TB.

Conclusions: Rhesus macaques are excellent model of TB/AIDS coinfection and can be used to study the phenomena of TB latency and reactivation.

Figure 1. The experimental design for Mtb/SIV co-infection in NHPs (A)

All animals were infected with ~ 500 CFU Mtb CDC1551. PE 1, PE 2 and PE 3 correspond to the different collection of clinical activities performed on the two groups of animals at different time-points, including prior to Mtb infection. 300 TCID50 SIV_mac239 in PBS buffer was introduced i.v. into six NHPs belonging to group II. The group I animals received placebo (PBS).

Figure 2. Clinical correlates of latent TB and reactivation

We studied change in body temperature, expressed as change in ^oF (A), change in percent body-weight (B), and serum CRP concentrations, expressed as mg/ml (C). Closed circles represent group I, while closed squares represent group II. Comparison of the survival percentages for Mtb-infected and Mtb/SIV co-infected NHPs (D). Closed circles represent group I, while closed squares represent group II.

Figure 3. Microbiological correlates of latent TB and reactivation

Mtb CFUs recovered from blood (A) and BAL (B) during different time periods of infection, both expressed as CFU/80 mL. Mtb CFUs at necropsy in BrLN (C), lung (D), spleen (E), liver (F) and kidney (G), expressed as CFU/gram of tissue. Plasma SIV viral copy number as assessed by quantitative RT-PCR (H), prior to and after SIV co-infection. Data is shown for NHPs in group II (closed squares), as well as group III (open squares) for control plasma (prior to SIV infection) and at weeks 10, 12 and 13 post Mtb-infection (i.e. weeks 1, 3 and 4 post-SIV infection) for both groups.

Figure 4. Pathology of latent and reactivation TB

Representative gross pathology images from the lungs of an NHP from group I (A) and II (B). Representative H&E stained images from the lungs of an NHP from group I (C) and II (D).

Figure 5. Co-localization of Mtb and SIV in the tissues of co-infected animals

Multi-label confocal microscopy was used to identify if Mtb and SIV co-localize in the lungs (A) or BrLNs (B) of co-infected animals. A representative image from each tissue is being shown. Specific signal was detected under differential interference contrast (DIC). SIV was detected by using a p28-specific antibody raised in mouse (Microbix Biosystems #AS-59-06) as previously described (28). Mtb was detected by using a polyclonal anti-Mtb antibody raised in rabbit (Abcam #ab905), as previously described (23).