BCG-specific IgG-secreting peripheral plasmablasts as a potential biomarker of active tuberculosis in HIV negative and HIV positive patients

Abstract

BackgroundDiagnosis of active tuberculosis (TB) among sputum-negative cases, patients with HIV infection and extra-pulmonary TB is difficult. In this study, assessment of BCG-specific IgG-secreting peripheral plasmablasts, was used to identify active TB in these high-risk groups.MethodsPeripheral blood mononuclear cells were isolated from patients with TB and controls and cultured in vitro using an assay called Antibodies in Lymphocyte Supernatant, which measures spontaneous IgG antibody release from migratory plasmablasts. A BCG-specific ELISA and flow cytometry were used to quantify in vivo activated plasmablasts in blood samples from Ethiopian subjects who were HIV negative or HIV positive. Patients diagnosed with different clinical forms of sputum-negative active TB or other diseases (n=96) were compared with asymptomatic individuals including latent TB and non-TB controls (n=85). Immunodiagnosis of TB also included the tuberculin skin test and the interferon (IFN)-γ release assay, QuantiFERON.ResultsThis study demonstrated that circulating IgG+ plasmablasts and spontaneous secretion of BCG-specific IgG antibodies were significantly higher in patients with active TB compared with latent TB cases and non-TB controls. BCG-specific IgG titres were particularly high among patients coinfected with TB and HIV with CD4 T-cell counts <200 cells/ml who produced low levels of Mycobacterium tuberculosis-specific IFNγ in vitro.ConclusionsThese results suggest that BCG-specific IgG-secreting peripheral plasmablasts could be successfully used as a host-specific biomarker to improve diagnosis of active TB, particularly in people who are HIV positive, and facilitate administration of effective treatment to patients. Elevated IgG responses were associated with impaired peripheral T-cell responses, including reduced T-cell numbers and low M tuberculosis-specific IFNγ production.

Evaluation of the Antibody in Lymphocyte Supernatant Assay to Detect Active Tuberculosis

“…Similar findings have been seen by Ashenafi et al in their cohort of 84 adults from Ethiopia with TB, including 27 with TB/HIV co-infection. Despite the majority of co-infected participants having CD4 + T-cell counts <200 cells/mm 3 , they also found that ALS responses did not differ significantly between those with HIV/TB compared to those with TB alone [5]. In conjunction these results affirm that this assay holds potential to fill a gap in the current biomarker landscape.…”

“…Although this is an antibody-based assay, it differs from traditional serologic tests by discarding the serum and measuring incident antibody production directly from the lymphocytes. Thus, it can serve as a biomarker of immune response to TB antigens that are present during active disease but not latent infection [5]. In this study, we aim to evaluate the performance of the ALS assay in diagnosing active TB and monitoring response to TB treatment among adults with and without HIV from Tanzania.…”

Year in review 2013: basic science and epidemiology

“…Molecular characterisation of clinical samples has revealed new subtypes of IPF, defined by expression of cilium-associated genes,19 while identification of BCG-specific IgG secreting peripheral plasmablasts as a potential biomarker may improve diagnosis of active tuberculosis (TB), particularly in those patients who also have HIV 20…”

T7 Phage Display Library a Promising Strategy to Detect Tuberculosis Specific Biomarkers

“…Opsonization through FcγR was shown to promote phagolysosomal fusion and intracellular killing [26,27]. Besides the well-known role of B cells in providing a robust T cell response against Mtb through secretion of various cytokines and chemokines, recent studies highlight the importance of B cells in the modulation of neutrophil function and granuloma formation [7,28-30]. In animal models, there is increasing evidence that mice with defective humoral immunity are more susceptible to TB.…”

“…Additionally, passive transfer of antibodies to Mtb antigens protects mice against TB [31,32]. Interestingly, Ashenafi et al [30] found that BCG-specific IgG-secreting peripheral plasmablasts could be successfully utilized as a host-specific biomarker for TB diagnosis, even in subjects with impaired T cell function, including HIV positive subjects, and subjects with culture negative TB. Thus, the detection of Mtb -specific antibody responses in sera of TB patients provides an important step not only for TB diagnosis but also for the development of new vaccines and monitoring of the immune response after vaccination.…”