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Paracoccidioides lutzii Plp43 is an active glucanase with partial antigenic identity with P. brasiliensis gp43
Natanael P Leitão1, Milene C Vallejo1, Palloma M Conceição1
1Departamento de Microbiologia, Imunologia e Parasitologia, Escola Paulista de Medicina-Universidade Federal de São Paulo (EPM-UNIFESP), São Paulo, Brazil.
Background:
Paracoccidioides brasiliensis and P. lutzii cause paracoccidioidomycosis (PCM). P. brasiliensis main diagnostic antigen is glycoprotein gp43, and its peptide sequence is 81% identical with a P. lutzii ortholog here called Plp43. P. lutzii ("Pb01-like") apparently predominates in Midwestern/Northern Brazil, where high percentages of false-negative reactions using P. brasiliensis antigens have recently been reported. The aim of this work was to produce recombinant Plp43 to study its antigenic identity with gp43.
Methodology:
We expressed rPlp43 as a secreted major component in Pichia pastoris and studied its reactivity in immunoblot with PCM patients' sera from Southwestern and Midwestern Brazil.
Principal Findings:
We showed that rPlp43 is not glycosylated and bears glucanase activity. The protein did not react with anti-gp43 monoclonal antibodies in immunoblot, suggesting absence of the corresponding gp43 epitopes. Nevertheless, common epitope(s) might exist, considering that gp43-positive PCM sera recognized rPlp43 in immunoblot, while gp43-negative sera (33 out of 51) from patients resident in Midwestern Brazil were also rPlp43-negative. Two genotyped P. lutzii were from patients with gp43-negative sera, suggesting that non-reactive sera are from patients infected with this species.
Conclusion:
Our data suggest that gp43 and Plp43 bear one or only a few common epitopes and that gp43 cannot be used in diagnosis of PCM patients infected with P. lutzii probably because Plp43 is poorly expressed during infection.
Insights
Recombinant Plp43, a P. lutzii antigen, shows limited cross-reactivity with P. brasiliensis gp43. This suggests gp43 may not accurately diagnose P. lutzii-caused paracoccidioidomycosis (PCM).
Area of Science:
- Mycology
- Immunology
- Infectious Diseases
Background:
- Paracoccidioidomycosis (PCM) is caused by *Paracoccidioides brasiliensis* and *P. lutzii*.
- The main diagnostic antigen for *P. brasiliensis* is glycoprotein gp43, with an 81% sequence identity to the *P. lutzii* ortholog, Plp43.
- *P. lutzii* infections are increasing in Brazil, coinciding with reported false-negative PCM diagnostic results using *P. brasiliensis* antigens.
Purpose of the Study:
- To produce recombinant Plp43 (rPlp43) from *P. lutzii*.
- To investigate the antigenic relationship between rPlp43 and gp43 from *P. brasiliensis*.
- To assess the utility of rPlp43 in diagnosing PCM, particularly in cases potentially caused by *P. lutzii*.
Main Methods:
- Recombinant Plp43 (rPlp43) was expressed in *Pichia pastoris*.
- The reactivity of rPlp43 was tested using immunoblots with sera from PCM patients in Southwestern and Midwestern Brazil.
- Monoclonal antibodies against gp43 and patient sera were used to evaluate epitope sharing.
Main Results:
- rPlp43 was found to be non-glycosylated and possess glucanase activity.
- rPlp43 did not react with anti-gp43 monoclonal antibodies, indicating a lack of shared gp43-specific epitopes.
- While some gp43-positive PCM sera recognized rPlp43, sera from Midwestern Brazil patients (often infected with *P. lutzii*) showed negative results for both gp43 and rPlp43.
Conclusions:
- Glycoprotein gp43 and Plp43 share minimal or no common epitopes.
- The diagnostic utility of gp43 for PCM is limited in cases caused by *P. lutzii*.
- Poor expression of Plp43 during *P. lutzii* infection may explain the lack of reactivity in diagnostic tests.
