title: Mycobacterium tuberculosis secretory proteins downregulate T cell activation by interfering with proximal and downstream T cell signalling events.
abstract: BACKGROUND
  Mycobacterium tuberculosis (M. tuberculosis) modulates host immune response, mainly T cell responses for its own survival leading to disease or latent infection. The molecules and mechanisms utilized to accomplish immune subversion by M. tuberculosis are not fully understood. Understanding the molecular mechanism of T cell response to M. tuberculosis is important for development of efficacious vaccine against TB.
  
  
  METHODS
  Here, we investigated effect of M. tuberculosis antigens Ag85A and ESAT-6 on T cell signalling events in CD3/CD28 induced Peripheral blood mononuclear cells (PBMCs) of PPD+ve healthy individuals and pulmonary TB patients. We studied CD3 induced intracellular calcium mobilization in PBMCs of healthy individuals and TB patients by spectrofluorimetry, CD3 and CD28 induced activation of mitogen activated protein kinases (MAPKs) in PBMCs of healthy individuals and TB patients by western blotting and binding of transcription factors NFAT and NFκB by Electrophorectic mobility shift assay (EMSA).
  
  
  RESULTS
  We observed CD3 triggered modulations in free intracellular calcium concentrations in PPD+ve healthy individuals and pulmonary TB patients after the treatment of M. tuberculosis antigens. As regards the downstream signalling events, phosphorylation of MAPKs, Extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 was curtailed by M. tuberculosis antigens in TB patients whereas, in PPD+ve healthy individuals only ERK1/2 phosphorylation was inhibited. Besides, the terminal signalling events like binding of transcription factors NFAT and NFκB was also altered by M. tuberculosis antigens. Altogether, our results suggest that M. tuberculosis antigens, specifically ESAT-6, interfere with TCR/CD28-induced upstream as well as downstream signalling events which might be responsible for defective IL-2 production which further contributed in T-cell unresponsiveness, implicated in the progression of disease.
  
  
  CONCLUSIONS
  To the best of our knowledge, this is the first study to investigate effect of Ag85A and ESAT-6 on TCR- and TCR/CD28- induced upstream and downstream signalling events of T-cell activation in TB patients. This study showed the effect of secretory antigens of M. tuberculosis in the modulation of T cell signalling pathways. This inflection is accomplished by altering the proximal and distal events of signalling cascade which could be involved in T-cell dysfunctioning during the progression of the disease.
authors.affiliation: Department of Immunology, National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Dr.M.Miyazaki Marg, Tajganj, Agra, 282001, India. bhavnamicrobio@gmail.com.
authors.forename: Bhawna
authors.initials: B
authors.lastname: Sharma
authors.affiliation: Department of Immunology, National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Dr.M.Miyazaki Marg, Tajganj, Agra, 282001, India. rajniupadhyay@gmail.com.
authors.forename: Rajni
authors.initials: R
authors.lastname: Upadhyay
authors.affiliation: Department of Immunology, National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Dr.M.Miyazaki Marg, Tajganj, Agra, 282001, India. bhavidua08@gmail.com.
authors.forename: Bhavyata
authors.initials: B
authors.lastname: Dua
authors.affiliation: UPRES EA 4183 Lipides & Signalisation Cellulaire, Faculté des Sciences de la vie, Université de Bourgogne, 6, Boulevard Gabriel, Dijon, 21000, France. Naim.Khan@u-bourgogne.fr.
authors.forename: Naim Akhtar
authors.initials: NA
authors.lastname: Khan
authors.affiliation: Formerly in Department of Health Research and ICMR, Ansari Nagar, New Delhi-29, India. vishwamohan_katoch@yahoo.co.in.
authors.forename: Vishwa Mohan
authors.initials: VM
authors.lastname: Katoch
authors.affiliation: State TB Training & Demonstration Centre, S.N. Medical College Campus, Agra, 282 002, India. bharatbajaj10062@gmail.com.
authors.forename: Bharat
authors.initials: B
authors.lastname: Bajaj
authors.affiliation: Department of Immunology, National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Dr.M.Miyazaki Marg, Tajganj, Agra, 282001, India. beenuj2002@yahoo.co.in.
authors.forename: Beenu
authors.initials: B
authors.lastname: Joshi
mesh_terms: D000217:Acyltransferases / Q000276:immunology / Q000378:metabolism; D000942:Antigens, Bacterial / Q000276:immunology / Q000378:metabolism; D001426:Bacterial Proteins / Q000276:immunology* / Q000378:metabolism*; D018106:CD28 Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000276:immunology / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000276:immunology* / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D018106:CD28 Antigens; C093276:ESAT-6 protein, Mycobacterium tuberculosis; D016328:NF-kappa B; D050778:NFATC Transcription Factors; D011948:Receptors, Antigen, T-Cell; C072681:Mycobacterium tuberculosis antigens; D000217:Acyltransferases; C112580:antigen 85A, Mycobacterium tuberculosis; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium