Mycobacterium tuberculosis Co-operonic PE32/PPE65 Proteins Alter Host Immune Responses by Hampering Th1 Response.

Mohd Khubaib,Saurabh Pandey,Nasreen Z Ehtesham,Battu Srikanth,Javaid A Sheikh,Nooruddin Khan,Manish Bhuwan,Seyed E Hasnain

doi:10.3389/fmicb.2016.00719

Mohd Khubaib, Saurabh Pandey + Show 6 more

Open Access

https://doi.org/10.3389/fmicb.2016.00719

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Abstract

PE/PPE genes, present in cluster with ESAT-6 like genes, are suspected to have a role in antigenic variation and virulence of Mycobacterium tuberculosis. Their roles in immune evasion and immune modulation of host are also well documented. We present evidence that PE32/PPE65 present within the RD8 region are co-operonic, co-transcribed, and co-translated, and play role in modulating host immune responses. Experiments with macrophage cell lines revealed that this protein complex suppresses pro-inflammatory cytokines such as TNF-α and IL-6 whereas also inducing high expression of anti-inflammatory IL-10. Immunization of mice with these recombinant proteins dampens an effective Th1 response as evident from reduced frequency of IFN-γ and IL-2 producing CD4+ and CD8+ T cells. IgG sub-typing from serum of immunized mice revealed high levels of IgG1 when compared with IgG2a and IgG2b. Further IgG1/IgG2a ratio clearly demonstrated that the protein complex manipulates the host immune response favorable to the pathogen. Our results demonstrate that the co-transcribed and co-translated PE32 and PPE65 antigens are involved specifically in modulating anti-mycobacterial host immune response by hampering Th1 response.

Highlights

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis), despite being completely curable, claimed more than 1.5 million human lives in 2013 alone (Zumla et al, 2015) and continue to do so
In silico analysis predicted several PE/PPE genes, including the PE32/PPE65 pair to be organized as operons in the genome (Tundup et al, 2006)
RT-PCR was carried out using specific reverse and forward primers of PPE65 and PE32 for amplification of PE32 (P1, P2), PPE65 (P3, P4), and PE32+PPE65 (P1, P4) were used (Table 1; Figure 1A)

Summary

Introduction

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (M. tuberculosis), despite being completely curable, claimed more than 1.5 million human lives in 2013 alone (Zumla et al, 2015) and continue to do so. The current protective TB vaccine- a live-attenuated M. bovis Bacillus-Calmette-Guerin (BCG) vaccine is protective against TB and leprosy in young people, but it is not efficient in protecting adults against pulmonary TB or reactivation of the latent TB infection (Mangtani et al, 2014) Proteins unique to these bacteria will be of interest in understanding the pathobiology of this bacterium. While M. tuberculosis genome encodes about 175 PE/PPE proteins (Cole, 1998), the recently sequenced ancestral, non-pathogenic and medically relevant M. indicus pranii carries only 66 PE/PPE genes (Saini et al, 2009, 2012) These genes were speculated to be introduced into mycobacteria by mobile elements via lateral gene transfer and later evolved from esx-encoded ancestral PE/PPE copies by gene duplication of this cluster (Gey van Pittius et al, 2006)

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