Detection of a combination of serum IgG and IgA antibodies against selected mycobacterial targets provides promising diagnostic signatures for active TB

// Dolapo O. Awoniyi 1, * , Ralf Baumann 1, 2, 3, * , Novel N. Chegou 1 , Belinda Kriel 1 , Ruschca Jacobs 1 , Martin Kidd 4 , Andre G. Loxton 1 , Susanne Kaempfer 3 , Mahavir Singh 3 and Gerhard Walzl 1 1 DST/NRF Centre of Excellence for Biomedical TB Research and SAMRC Centre for TB Research, Division of Molecular Biology and Human Genetics, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa 2 Institute for Occupational and Social Medicine, Aachen University of Technology, Aachen, Germany 3 Lionex Diagnostics and Therapeutics, Braunschweig, Germany 4 Centre for Statistical Analysis, Stellenbosch University, Stellenbosch, South Africa * These authors have contributed equally to this work Correspondence to: Gerhard Walzl, email: gwalzl@sun.ac.za Keywords: tuberculosis, diagnosis, biomarker, antibody, Ig class Received: November 25, 2016     Accepted: February 27, 2017     Published: March 21, 2017 ABSTRACT Immunoglobulin G (IgG) based tests for the diagnosis of active tuberculosis (TB) disease often show a lack of specificity in TB endemic regions, which is mainly due to a high background prevalence of LTBI. Here, we investigated the combined performance of the responses of different Ig classes to selected mycobacterial antigens in primary healthcare clinic attendees with signs and symptoms suggestive of TB. The sensitivity and specificity of IgA, IgG and/or IgM to LAM and 7 mycobacterial protein antigens (ESAT-6, Tpx, PstS1, AlaDH, MPT64, 16kDa and 19kDa) and 2 antigen combinations (TUB, TB-LTBI) in the plasma of 63 individuals who underwent diagnostic work-up for TB after presenting with symptoms and signs compatible with possible active TB were evaluated. Active TB was excluded in 42 individuals of whom 21 has LTBI whereas active TB was confirmed in 21 patients of whom 19 had a follow-up blood draw at the end of 6-month anti-TB treatment. The leading single serodiagnostic markers to differentiate between the presence or absence of active TB were anti-16 kDa IgA, anti-MPT64 IgA with sensitivity and specificity of 90%/90% and 95%/90%, respectively. The combined use of 3 or 4 antibodies further improved this performance to accuracies above 95%. After successful completion of anti-TB treatment at month 6, the levels of 16 kDa IgA and 16 kDa IgM dropped significantly whereas LAM IgG and TB-LTBI IgG increased. These results show the potential of extending investigation of anti-tuberculous IgG responses to include IgM and IgA responses against selected protein and non-protein antigens in differentiating active TB from other respiratory diseases in TB endemic settings.