Immune reactivity to tuberculosis and candida antigens in subjects with latent tuberculosis infection and unexposed subjects: A validation cohort study

Abstract

Abstract Rationale Candida albicans (CA) is ubiquitous and individuals are often immunized against it. However, skin testing reactivity with CA-antigens (CAAg) have been variable during latent tuberculosis infection (LTBI) screening. We hypothesized that the use of a CAAg in an ELISPOT assay would provide a positive control to study tuberculosis (TB)-antigen specific immune responses. Objective To test an ELISPOT with TB-antigens and control conditions, including a purified protein derivative of CA, CAAg, that differentiates subjects with LTBI from unexposed subjects. Methods An ELISPOT that detects interferon-γ from PBMCs (2×105 cells) after 2-day incubation with TB antigens, controls, including CAAg, and co-stimulatory antibodies. We studied two independent cohorts of subjects with LTBI diagnosis based on TST and IGRA results per clinical guidelines. Results One-hundred thirty-nine subjects were studied in 2010–12, including 27 patients with LTBI and 21 IGRA(−) unexposed subjects. ELISPOT with TB-antigens but also CAAg - nil (78 [21 – 182] vs. 9 [1 – 50] cfu) differentiated LTBI subjects from unexposed ones (P<0.005). A second cohort of 76 subjects were studied in 2015–17, including 14 patients with LTBI and 24 unexposed controls, which showed similar statistical results. Positive control (SEAB/antiCD3) did not differentiate these study groups. ELISPOT results with CAAg correlated with results of ELISPOT with TB antigens in all subjects (P<0.001), and in the LTBI and unexposed groups independently. Conclusion An ELISPOT assay that includes CAAg revealed immune reactivity that is prevalent in LTBI. The immune subsets that react to both CA and mycobacterial antigens are unclear, but may be relevant for both TB and candida immunity.