(500) Immunoglobulins in Saliva as a Culture-Independent Marker of Nontuberculous Mycobacterial Infection in Cystic Fibrosis

Background: People with cystic fibrosis (pwCF) are at high risk for developing nontuberculous mycobacterial (NTM) lung infection and disease. Detection of these infections remains difficult due to the slow growth and low sensitivity of traditional sputum culture. This is further complicated by widespread use of highly effective modulator therapy in pwCF, often making sputum samples unavailable. There is now an urgent need to develop culture-independent markers of NTM infection that equal or surpass the sensitivity and specificity of cultures. Prior work has indicated utility in measuring anti-NTM immunoglobulins in plasma as a potential biomarker for NTM disease. This study tests the Hypothesis: Anti-NTM IgA and IgG in saliva are a sensitive culture-independent biomarker for NTM disease.

Methods: Saliva samples were weighed, aliquoted, and stored at -80 C. Cocktails of heat-killed M. abscessus were plated and dried in 96-well plates. Plates were then blocked with bovine serum albumin (BSA) and incubated with diluted patient saliva samples. Wells were washed with PBS and bound antibody detected with HRP-conjugated goat anti-human antibodies specific for NTM IgA and IgG using immunofluorescence. Values for IgA and IgG were analyzed independently and in summation.

Results: Saliva samples from pwCF who met ATS criteria for NTM lung disease within a year of their last culture with M. avium complex or M. abscessus (N=12) were compared to saliva samples from pwCF either always negative for NTM or negative for NTM for at least the past 3 years (N=24). Patients with known NTM disease had a statistically significant higher level of NTM anti-IgA and anti-IgG found in their saliva compared to culture negative patients (p=0.01 by T-test) with a sensitivity of 58% and specificity of 79% with a binary classification two standard deviations above the mean. There was no difference in immunoglobulin level between subjects with M. avium complex or M. abscessus.

Conclusions: Saliva samples are much easier to obtain compared to sputum, thus, identifying a saliva biomarker has the potential to improve how we diagnose NTM disease in pwCF, particularly in children and adults unable to expectorate sputum. Although limited by sample size, our preliminary data from this study indicates that detection of high levels of anti-NTM IgA and IgG in the saliva of CF patients has the potential to be used as a culture-independent biomarker of NTM lung disease caused by either M. abscessus or M. avium complex. This study is ongoing and will be updated with additional data.

Acknowledgements: This work was supported by the Cystic Fibrosis Foundation (NICK21K0, NICK17K0, NICK20A0, NICK20Y2OUT).

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