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Major basic protein homolog (MBP2): a specific human eosinophil marker
Douglas A Plager1, David A Loegering, James L Checkel
1Allergic Diseases Research Laboratory, Mayo Clinic and Foundation, Rochester, MN 55905, USA. plager.douglas@mayo.edu
Abstract:
Human eosinophil granule major basic protein (MBP1) is an exceedingly basic (isoelectric point >11) 14-kDa protein, comprising the core of the secondary eosinophil granule. Recently, a less cationic homolog of MBP, termed MBPH or simply, MBP2, has been discovered. We prepared a panel of mAbs to MBP2 and used these Abs to localize and quantitate this molecule in leukocytes and biological fluids. Specific mAbs for MBP2 were selected using slot-blot analyses and used in a two-site immunoassay, Western blotting, and immunofluorescence microscopy. The sensitivity of the immunoassay was markedly improved by reduction and alkylation of MBP2. MBP1 is more abundant than MBP2 in lysates of eosinophils and their granules, as judged by immunoassay and Western blotting. By immunofluorescence, MBP1 is present in eosinophils, basophils, and a human mast cell line (HMC1), whereas MBP2 is only detected in eosinophils. Neither MBP1 nor MBP2 could be detected in any other peripheral blood leukocyte. MBP2 levels measured in plasma and serum were essentially identical. In contrast to past measurements for MBP1, MBP2 was not detected above normal levels in sera from pregnant donors. However, measurement of serum MBP2 discriminated patients with elevated eosinophils from normal subjects, and MBP2 was also detectable in other biological specimens, such as bronchoalveolar lavage, sputum, and stool. These results indicate that MBP2 is present only in eosinophils and that it may be a useful biomarker for eosinophil-associated diseases.
Insights
Major basic protein 2 (MBP2) is a novel eosinophil protein. Unlike MBP1, MBP2 is found exclusively in eosinophils and may serve as a valuable biomarker for eosinophil-associated diseases.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Human eosinophil granules contain major basic protein (MBP1), a highly cationic protein.
- A less cationic homolog, major basic protein 2 (MBP2), has been recently identified.
Purpose of the Study:
- To develop and utilize monoclonal antibodies (mAbs) for the localization and quantification of MBP2.
- To compare the distribution and abundance of MBP1 and MBP2 in various cell types and biological fluids.
Main Methods:
- Development of specific mAbs against MBP2.
- Application of slot-blot, two-site immunoassay, Western blotting, and immunofluorescence microscopy.
- Optimization of immunoassay sensitivity through reduction and alkylation.
Main Results:
- MBP2 is exclusively detected in eosinophils, unlike MBP1 which is also found in basophils and mast cells.
- MBP1 is more abundant than MBP2 in eosinophil lysates and granules.
- Serum MBP2 levels effectively differentiated patients with elevated eosinophils from normal subjects and were detectable in other biological samples.
Conclusions:
- MBP2 is a specific marker for eosinophils.
- MBP2 shows potential as a biomarker for diagnosing and monitoring eosinophil-associated diseases.
