Anti-MSAD-1 humoral immunity: a novel biomarker in NTM-PD

To The Editor: The host defense mechanisms against nontuberculous mycobacteria (NTM) remain poorly understood, and most patients with NTM-pulmonary disease (PD) lack defects in cell-mediated immunity,1 shifting the focus toward humoral immunity. Malonate semialdehyde decarboxylase-1 (MSAD-1), originating from various bacteria, including Pseudomonas pavonaceae, is specifically found in pathogenic NTM such as Mycobacterium avium complex and Mycobacterium abscessus, whereas Mycobacterium tuberculosis has no ortholog in its genome.2 We hypothesized that patients with NTM-PD exhibit a unique antibody response against MSAD-1, which may contribute to disease susceptibility by limiting bacterial clearance. To test this hypothesis, we performed antibody analysis with Fc receptor-binding assays using serum and respiratory specimens. Serum samples were obtained from patients with NTM-PD at Seoul National University Hospital between October 2011 and December 2017 as part of a prospective cohort study (ClinicalTrials.gov identifier: NCT01616745). Samples were collected at diagnosis before antibiotic treatment. Disease controls were patients with pulmonary tuberculosis (TB) during the same period, and healthy controls were participants without comorbidities (NCT03120481).