IgA Serological Response for the Diagnosis of Mycobacterium abscessus Infections in Patients with Cystic Fibrosis

Abstract

The immunoglobulin A (IgA) status of cystic fibrosis (CF) patients, presenting with or without a non-tuberculous mycobacterial (NTM) infection, has to date not been fully elucidated toward two antigenic preparations previously described. We have chosen to determine the clinical values of an IgA ELISA for the diagnosis of NTM and/or Mycobacterium abscessus infections in CF patients. One hundred and 73 sera from CF patients, comprising 33 patients with M. abscessus positive cultures, and 31 non-CF healthy controls were assessed. IgA levels were evaluated by indirect ELISAs using a surface antigenic extract named TLR2eF for TLR2 positive extract and a recombinant protein, the phospholipase C (rMAB_0555 or rPLC). These assays revealed a sensitivity of 52.6% (95% CI = 35.8% to 69%) and 42.1% (95% CI = 26.3% to 59.2%) using TLR2eF and rPLC, respectively, and respective specificities of 92.6% (95% CI = 87.5% to 96.1%) and 92% (95% CI = 86.7% to 95.7%) for samples culture positive for M. abscessus. Overall sensitivity and specificity of 66.7% and 85.4%, respectively, were calculated for IgA detection in M. abscessus-culture positive CF patients, when we combine the results of the two used antigens, thus demonstrating the efficiency in detection of positive cases for these two antigens with IgA isotype. CF patients with a positive culture for M. abscessus had the highest IgA titers against TLR2eF and rPLC. The diagnosis of NTM infections, including those due to M. abscessus, can be improved by the addition of an IgA serological assay, especially when cultures, for example, are negative. Based on these promising results, a serological follow-up of a larger number of patients should be performed to determine if the IgA response may be correlated with an active/acute infection state or a very recent infection. IMPORTANCE Mycobacterium abscessus is currently the most frequently isolated rapid growing mycobacterium in human pathology and the major one involved in lung infections. It has recently emerged as responsible for severe pulmonary infections in patients with cystic fibrosis (CF) or those who have undergone lung transplantation. In addition, it represents the most antibiotic resistant mycobacterial species. However, despite its increasing clinical importance, very little is known about the use of M. abscessus parietal compounds and the host response. This has led to the development of serological tests to measure the antibody response in infected patients, and potentially to link this to the culture of respiratory samples. Herein, we describe an important analysis of the serological IgA response from CF patients, and we demonstrate the full diagnostic usefulness of this assay in the diagnosis of NTM infections, and more particularly M. abscessus, in CF patients.

Keywords: ELISA; IgA; cystic fibrosis; non-tuberculous mycobacteria; serodiagnosis; serology.

FIG 1

IgA response of NTM positive culture, non-NTM positive culture groups and healthy control (HC) group using TLR2eF (A) and rPLC (B) as antigens. Each dot represents one patient in the scattergrams. Horizontal lines represent the mean and vertical bars SDs. Values are presented in Tables S1A and S1B in the supplemental material for each antigenic sample, respectively. Chosen cut-off values (test positivity threshold) are respectively 0.751 (A) and 1.274 (B) (dotted horizontal lines). P < 0.001 for comparisons of NTM-culture positive groups versus the non-NTM group plus the HC group for TLR2eF and rPLC. Beneath each figure is represented the corresponding 2 by 2 table for NTM-culture positive patients. n.s., nonsignificant; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.

FIG 2

IgA response of the different cystic fibrosis (CF) patient groups and healthy control (HC) group using TLR2eF (A) or rPLC (B) as antigen. Each dot represents one patient in the scattergrams. In MAC group, yellow squares represent M. avium-, pink squares represent M. chimaera- and red squares M. intracellulare-culture positive-CF patients. Horizontal lines represent the mean and vertical bars SDs. Chosen cut-off values (test positivity threshold) are 0.751 and 1.274 in A and B, respectively (dotted horizontal lines). Beneath each figure is represented the corresponding 2 by 2 table, for Mabs culture positive-CF patients, and see the 2 by 2 Tables S2A and S2B in the supplemental material for MAC culture positive-CF patients. n.s., nonsignificant; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.