Abstract

Backgrouds and Aims: Autoimmune pulmonary alveolar proteinosis (APAP) is caused by neutralizing autoantibody against GM-CSF. We have demonstrated that IgG antibody levels in serum can predict clinical courses of APAP (1); however, they were not correlated with other clinical characteristics of patients. We measured neutralizing capacity of serum antibody and examined correlation between NCAP and physiological and radiological features in APAP patients.

Methods: APAP was diagnosed in 52 patients (27 men and 25 women, mean age 55 yr [SD 15]) based on pathological and/or bronchoalveolar lavage findings and the presence of autoantibody against GM-CSF in serum. IgG antibody levels against GM-CSF was measured by ELISA. Neutralizing capacity of each serum was assessed by measuring 50% inhibitory concentration (IC₅₀) of serum antibody levels to the growth of GM-CSF dependent TF-1 cells. Extent of lung shadows on CT was semi-quantified by the modified scoring method as previously described (2). Relationship between IC₅₀ and other parameters was assessed by Pearson's correlation coefficients.

Results: There were no significant correlation between IC₅₀ and total antibody levels; however, IC₅₀ were positively correlated with percent diffusing capacity of carbon monoxide and negatively correlated with total scores of lung shadows on CT. Total antibody levels devided by IC₅₀ were positively correlated with total scores of lung shadows.

Conclusion: Neutralizing capacity of serum autoantibody substantially affects lung physiology and the extent of shadows in APAP patients.

1. Nishimura M, et al, Biomark Med. 2018, 12:151. 

2. Tazawa R, et al, Am J Respir Crit Care Med. 2010, 181:1345.