Standardized serum GM-CSF autoantibody testing for the routine clinical diagnosis of autoimmune pulmonary alveolar proteinosis.

Autoantibodies against granulocyte/macrophage colony-stimulating factor (GMAbs) cause autoimmune pulmonary alveolar proteinosis (PAP) and measurement of the GMAb level in serum is now commonly used to identify this disease, albeit, in a clinical research setting. The present study was undertaken to optimize and standardize serum GMAb concentration testing using a GMAb enzyme-linked immunosorbent assay (GMAb ELISA) to prepare for its introduction into routine clinical use. The GMAb ELISA was evaluated using serum specimens from autoimmune PAP patients, healthy people, and GMAb-spiked serum from healthy people. After optimizing assay components and procedures, its accuracy, precision, reliability, sensitivity, specificity, and ruggedness were evaluated. The coefficient of variation in repeated measurements was acceptable (<15%) for well-to-well, plate-to-plate, day-to-day, and inter-operator variation, and was not affected by repeated freeze-thaw cycles of serum specimens or the reference standards, or by storage of serum samples at -80°C. The lower limit of quantification (LLOQ) of the PAP patient-derived polyclonal GMAb reference standard (PCRS) was 0.78ng/ml. Receiver operating characteristic curve analysis identified a serum GMAb level of 5µg/ml (based on PCRS) as the optimal cut off value for distinguishing autoimmune PAP serum from normal serum. A pharmaceutical-grade, monoclonal GMAb reference standard (MCRS) was developed as the basis of a new unit of measure for GMAb concentration: one International Unit (IU) of GMAb is equivalent to 1µg/ml of MCRS. The median [interquartile range] serum GMAb level was markedly higher in autoimmune PAP patients than in healthy people (21.54 [12.83-36.38] versus 0.08 [0.05-0.14] IU; n=56, 38; respectively; P<0.0001). Results demonstrate that serum GMAb measurement using the GMAb ELISA was accurate, precise, reliable, had an acceptable LLOQ, and could be accurately expressed in standardized units. These findings support the use of this GMAb ELISA for the routine clinical diagnosis of autoimmune PAP and introduce a new unit of measure to enable standardized reporting of serum GMAb data from different laboratories.

Hereditary pulmonary alveolar proteinosis: pathogenesis, presentation, diagnosis, and therapy.

RATIONALE: We identified a 6-year-old girl with pulmonary alveolar proteinosis (PAP), impaired granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor function, and increased GM-CSF. OBJECTIVES: Increased serum GM-CSF may be useful to identify individuals with PAP caused by GM-CSF receptor dysfunction. METHODS: We screened 187 patients referred to us for measurement of GM-CSF autoantibodies to diagnose autoimmune PAP. Five were children with PAP and increased serum GM-CSF but without GM-CSF autoantibodies or any disease causing secondary PAP; all were studied with family members, subsequently identified patients, and controls. MEASUREMENT AND MAIN RESULTS: Eight children (seven female, one male) were identified with PAP caused by recessive CSF2RA mutations. Six presented with progressive dyspnea of insidious onset at 4.8 ± 1.6 years and two were asymptomatic at ages 5 and 8 years. Radiologic and histopathologic manifestations were similar to those of autoimmune PAP. Molecular analysis demonstrated that GM-CSF signaling was absent in six and severely reduced in two patients. The GM-CSF receptor ß chain was detected in all patients, whereas the α chain was absent in six and abnormal in two, paralleling the GM-CSF signaling defects. Genetic analysis revealed multiple distinct CSF2RA abnormalities, including missense, duplication, frameshift, and nonsense mutations; exon and gene deletion; and cryptic alternative splicing. All symptomatic patients responded well to whole-lung lavage therapy. CONCLUSIONS: CSF2RA mutations cause a genetic form of PAP presenting as insidious, progressive dyspnea in children that can be diagnosed by a combination of characteristic radiologic findings and blood tests and treated successfully by whole-lung lavage.

Granulocyte/macrophage-colony-stimulating factor autoantibodies and myeloid cell immune functions in healthy subjects.

High levels of granulocyte/macrophage-colony-stimulating factor (GM-CSF) autoantibodies are thought to cause pulmonary alveolar proteinosis (PAP), a rare syndrome characterized by myeloid dysfunction resulting in pulmonary surfactant accumulation and respiratory failure. Paradoxically, GM-CSF autoantibodies have been reported to occur rarely in healthy people and routinely in pharmaceutical intravenous immunoglobulin (IVIG) purified from serum pooled from healthy subjects. These findings suggest that either GM-CSF autoantibodies are normally present in healthy people at low levels that are difficult to detect or that serum pooled for IVIG purification may include asymptomatic persons with high levels of GM-CSF autoantibodies. Using several experimental approaches, GM-CSF autoantibodies were detected in all healthy subjects evaluated (n = 72) at low levels sufficient to rheostatically regulate multiple myeloid functions. Serum GM-CSF was more abundant than previously reported, but more than 99% was bound and neutralized by GM-CSF autoantibody. The critical threshold of GM-CSF autoantibodies associated with the development of PAP was determined. Results demonstrate that free serum GM-CSF is tightly maintained at low levels, identify a novel potential mechanism of innate immune regulation, help define the therapeutic window for potential clinical use of GM-CSF autoantibodies to treat inflammatory and autoimmune diseases, and have implications for the pathogenesis of PAP.

Familial pulmonary alveolar proteinosis caused by mutations in CSF2RA.

Primary pulmonary alveolar proteinosis (PAP) is a rare syndrome characterized by accumulation of surfactant in the lungs that is presumed to be mediated by disruption of granulocyte/macrophage colony-stimulating factor (GM-CSF) signaling based on studies in genetically modified mice. The effects of GM-CSF are mediated by heterologous receptors composed of GM-CSF binding (GM-CSF-Ralpha) and nonbinding affinity-enhancing (GM-CSF-Rbeta) subunits. We describe PAP, failure to thrive, and increased GM-CSF levels in two sisters aged 6 and 8 yr with abnormalities of both GM-CSF-Ralpha-encoding alleles (CSF2RA). One was a 1.6-Mb deletion in the pseudoautosomal region of one maternal X chromosome encompassing CSF2RA. The other, a point mutation in the paternal X chromosome allele encoding a G174R substitution, altered an N-linked glycosylation site within the cytokine binding domain and glycosylation of GM-CSF-Ralpha, severely reducing GM-CSF binding, receptor signaling, and GM-CSF-dependent functions in primary myeloid cells. Transfection of cloned cDNAs faithfully reproduced the signaling defect at physiological GM-CSF concentrations. Interestingly, at high GM-CSF concentrations similar to those observed in the index patient, signaling was partially rescued, thereby providing a molecular explanation for the slow progression of disease in these children. These results establish that GM-CSF signaling is critical for surfactant homeostasis in humans and demonstrate that mutations in CSF2RA cause familial PAP.