Antibody response against Mycobacterium avium complex in cystic fibrosis patients measured by a novel IgG ELISA test

Abstract

Background: Early signs of Mycobacterium avium complex pulmonary disease can be missed in patients with cystic fibrosis due to subclinical infection or delays in mycobacterial culture. The aim of this study was to determine the diagnostic accuracy of a novel enzyme linked immunosorbent assay for immunoglobulin G against Mycobacterium avium complex, which could help stratify patients according to risk. Methods: A retrospective cross sectional analysis of serum samples from the Copenhagen Cystic Fibrosis Center was performed. Corresponding clinical data were reviewed and patients with cystic fibrosis were assigned to one of four groups based on their mycobacterial culture results. In addition, anti-Mycobacterium avium complex immunoglobulin G levels were measured longitudinally before and after first positive culture in the period 1984-2015. Results: Three-hundred and five patients with cystic fibrosis were included with a median of five nontuberculous mycobacterial cultures. Four individuals had Mycobacterium avium complex pulmonary disease at the time of cross sectional testing and their median antibody level was 22-fold higher than patients with no history of infection (1820 vs. 80 IgG units; p b 0.001). Test sensitivity was 100% (95% CI 40-100) and specificity 77% (95% CI 72-81). Longitudinal kinetics showed rising antibodies prior to first positive culture suggesting diagnostic delay. Conclusions: Antibody screening for Mycobacterium avium complex may be used as a supplement to culture. Although confirmation in a larger cohort is needed, our findings suggest that stratifying a cystic fibrosis population into high-and low-risk groups based on antibody levels may help clinicians identify patients in need of more frequent culture.

Adaptive Immune Response to Mycobacterium abscessus Complex (MABSC) in Cystic Fibrosis and the Implications of Cross-Reactivity

“…As mentioned, mycobacteria share a number of antigens that may trigger both T and B cell responses ( Checkley et al., 2011 ; Qvist et al., 2015b ; Qvist et al., 2017 ; Ravnholt et al., 2019 ), which has also been shown in a recent study using four MABSC antigens and two recombinant proteins ( Le Moigne et al., 2021 ). As our in-house MABSC lysate is produced by means of X-press and sonication ( Closs et al., 1980 ), it contains common mycobacterial antigens ( Høiby et al., 1987 ; Qvist et al., 2015b ), allowing us to measure a broader immune response to environmental NTM.…”

“…Ideally, a similar approach would be preferable for diagnosing MABSC and other NTM in CF patients. Until that happens, however, cross-reactive responses among NTM may be used to diagnose latent or subclinical NTM infection in CF patients where the bacteria cannot be easily found and identified by routine culture- or molecular-based methods ( Hjelt et al, 1994 ; Qvist et al., 2015a ; Qvist et al., 2015b ; Ravnholt et al., 2019 ). Our plan is, therefore, to carry out a prospective study to explore whether measuring both anti-MABSC IgG and the production of MABSC-lysate-induced IFN-γ (and possibly also TNF-α and IL-2) by blood cells will be useful for early diagnosis of NTM infections.…”

“…We have previously shown that serum anti-MABSC IgG antibodies rise before and during clinical infection and can be used for diagnosis, although their protective capacity is unclear, which is also the case in P. aeruginosa infection. In some cases, MABSC IgG rose several months or years before MABSC isolation in culture ( Qvist et al., 2015b ), indicating latent or subclinical infection, which is well-known to be the case for Mycobacterium tuberculosis ( Oh et al., 2020 ), and was also the seen in CF patients with MAC infection ( Qvist et al., 2017 ; Ravnholt et al., 2019 ). We also found cross-reactivity between MABSC and other NTM when measuring either anti-MABSC or anti-MAC serum IgG ( Qvist et al., 2017 ; Ravnholt et al., 2019 ), in accordance with the genetic relatedness of NTM species ( Pereira et al., 2020 ).…”

“…In some cases, MABSC IgG rose several months or years before MABSC isolation in culture ( Qvist et al., 2015b ), indicating latent or subclinical infection, which is well-known to be the case for Mycobacterium tuberculosis ( Oh et al., 2020 ), and was also the seen in CF patients with MAC infection ( Qvist et al., 2017 ; Ravnholt et al., 2019 ). We also found cross-reactivity between MABSC and other NTM when measuring either anti-MABSC or anti-MAC serum IgG ( Qvist et al., 2017 ; Ravnholt et al., 2019 ), in accordance with the genetic relatedness of NTM species ( Pereira et al., 2020 ). Interestingly, a study showed that both the presence of Mycobacterium tuberculosis infection and the Bacillus Calmette-Guérin (BCG) vaccine (composed of an inactivated Mycobacterium bovis strain), induced cross-reactive lymphocyte response against MABSC and MAC in mice and humans ( Abate et al., 2019 ).…”

Specificity of Immunoglobulin Response to Nontuberculous Mycobacteria Infection in People with Cystic Fibrosis

“…NTM infection status has been estimated by measuring anti-MAC antibodies in plasma ( 16 – 20 ). These studies consistently detect samples from culture-positive subjects and discriminate between subjects with and without pulmonary disease and correlate with treatment outcome ( 16 – 19 ). However, these methods poorly discriminated MABSC from MAC infections ( 19 – 21 ), likely due to the use of single, common mycobacterial antigens.…”