interferon-gamma release assays

interferon-gamma release assays

Introduction

Interferon-gamma release assays are blood tests used to detect immune sensitization to Mycobacterium tuberculosis by measuring T lymphocyte–derived interferon-gamma after antigen exposure. Developed for clinical diagnostics, these assays intersect with public health programs, hospital infection control, occupational health screening, and global tuberculosis initiatives. They are integrated into guidelines from bodies such as the World Health Organization, Centers for Disease Control and Prevention, National Institute for Health and Care Excellence, and national tuberculosis programs in settings like India, South Africa, and Brazil.

Principles and mechanism

Assays exploit cellular immunity: peripheral blood mononuclear cells from a venous sample are incubated with peptide antigens derived from M. tuberculosis proteins, prompting antigen-specific CD4+ and CD8+ T cells to release interferon-gamma. The cytokine is quantified by enzyme-linked immunosorbent assay platforms linked to manufacturers and laboratories used by institutions such as Roche, Qiagen, Abbott, and local reference laboratories affiliated with university hospitals like Johns Hopkins, Karolinska Institutet, and University of Cape Town. The antigen panels commonly include ESAT-6 and CFP-10 peptides, which discriminate M. tuberculosis from Mycobacterium bovis BCG vaccination effects and many non-tuberculous mycobacteria encountered in regions like China, Russia, and Nigeria. Immunological readouts are interpreted in the context of host factors (HIV infection status, immunosuppressive therapies like infliximab or corticosteroids), demographic factors assessed by agencies such as Medicare and NHS England, and exposure history traced by contact investigations led by municipal health departments and global partners like Médecins Sans Frontières.

Types of assays

Major commercial formats include whole-blood ELISA-based tests and enzyme-linked immunospot assays performed in clinical laboratories connected to medical centers like Massachusetts General Hospital, Stanford Health Care, and Guy’s and St Thomas’ NHS Foundation Trust. Popular platforms include QuantiFERON assays produced by Qiagen and T-SPOT assays produced by Oxford Immunotec, each adopted in screening programs run by organizations such as the American Thoracic Society and the European Centre for Disease Prevention and Control. Research laboratories at institutions such as Pasteur Institute and Fred Hutchinson Cancer Center have developed modified ELISPOT protocols and multiplex cytokine panels used in epidemiologic studies funded by agencies like the Bill & Melinda Gates Foundation and National Institutes of Health.

Clinical applications

Clinically, assays are used to screen for latent tuberculosis infection in contacts of index cases identified in outbreak investigations by municipal health departments, in candidates for immunosuppressive therapy evaluated by transplant centers like Mayo Clinic, and among healthcare workers in hospitals such as Cleveland Clinic and Imperial College Healthcare. Public health programs in countries including Canada, Japan, and Australia incorporate these tests into migrant screening, prison screening led by correctional health services, and pre-employment occupational health protocols administered by corporate occupational clinics and labor unions. Assays support TB elimination strategies promoted by partnerships including Stop TB Partnership and national ministries of health, and they inform decisions about preventive therapy advocated by professional societies such as Infectious Diseases Society of America and Royal College of Physicians.

Performance and interpretation

Test performance metrics such as sensitivity, specificity, positive predictive value, and negative predictive value are reported in evaluations by academic centers like University of California, San Francisco, and Karolinska Institutet, and in systematic reviews by Cochrane and WHO technical groups. Interpretation requires consideration of pretest probability estimated from contact investigations run by local public health departments, prevalence data from surveillance systems operated by CDC and ECDC, and patient-specific risks managed by clinicians at institutions like Vanderbilt University Medical Center. Borderline or indeterminate results lead to repeat testing or alternative diagnostics such as chest imaging at radiology departments (Mayo Clinic Radiology, Royal Marsden) and microbiologic assays performed in reference laboratories like Public Health England and Institut Pasteur.

Limitations and sources of error

Limitations include reduced sensitivity in immunocompromised hosts (HIV clinics, oncology centers, rheumatology units administering biologics), variability due to preanalytical factors (delayed incubation, improper storage during transport from remote clinics in sub-Saharan Africa or rural India), and cross-reactivity from non-tuberculous mycobacteria encountered in environmental surveys conducted by US Geological Survey or national laboratories. Operational errors can arise in decentralized screening programs organized by occupational health services for airlines, military healthcare systems such as Veterans Health Administration, and correctional facilities. Economic and access issues affect implementation in low-resource settings supported by UNICEF, Global Fund, and local ministries of health.

History and development

The conceptual basis for in vitro lymphocyte stimulation and cytokine detection traces to immunology research at institutions such as Rockefeller University, University of Oxford, and University of Pennsylvania, and to early cytokine biology work by scientists recognized with awards like the Lasker Award. Technological commercialization involved companies such as Cellestis and Qiagen; clinical adoption expanded through guideline endorsements from WHO, CDC, and national professional societies. Field implementation was shaped by global health campaigns led by WHO Stop TB Partnership, philanthropic support from the Bill & Melinda Gates Foundation, and operational research conducted by partners including Partners In Health and Médecins Sans Frontières.

Category:Immunology