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Proline-rich vaccine candidate antigen of Coccidioides immitis: conservation among isolates and differential
T Peng1, K I Orsborn, M J Orbach
1Research and Medical Services, VA Medical Center, Tucson, Arizona, USA.
Abstract:
A proline rich antigen (PRA), which protects mice against Coccidioides immitis, has been analyzed for differential expression and variation among isolates. Northern blots of RNA from different stages of growth were probed with previously cloned cDNA and showed that mRNA for PRA increased as spherules transformed and matured from mycelia. This pattern corresponds to the relative potency of whole cell vaccines from similar preparations. The PRA gene was then cloned from a genomic library of the Silveira strain of C. immitis and its sequence analyzed. Eight other coccidioidal isolates, selected for diversity in geographic origin and resulting clinical disease, demonstrated heterogeneity in Southern blots and in sequences of polymerase chain reaction products. Silveira differed from other California isolates at 33 of 555 bases, whereas it differed from non-California isolates by <=2 bases. Only one of these substitutions affected protein sequence. Thus, tests or vaccines based on this gene are likely to cover most isolates.
Insights
A proline-rich antigen (PRA) shows increased expression during Coccidioides immitis development, suggesting its potential for vaccines. Genetic analysis reveals variations among isolates, but most are covered by PRA-based tests.
Area of Science:
- Mycology
- Immunology
- Molecular Biology
Background:
- Coccidioides immitis is a fungal pathogen causing coccidioidomycosis.
- A proline-rich antigen (PRA) has demonstrated protective effects in mouse models against C. immitis.
- Understanding antigen expression and genetic diversity is crucial for developing effective vaccines.
Purpose of the Study:
- To analyze the differential expression of the PRA gene during C. immitis growth stages.
- To investigate the genetic variation of the PRA gene among different C. immitis isolates.
- To assess the potential of PRA-based vaccines against diverse C. immitis strains.
Main Methods:
- Northern blot analysis of RNA from various growth stages.
- Cloning of the PRA gene from the Silveira strain.
- DNA sequencing of polymerase chain reaction products from multiple isolates.
- Southern blot analysis to detect genetic heterogeneity.
Main Results:
- PRA mRNA levels increased as C. immitis spherules matured from mycelia.
- Significant genetic heterogeneity was observed among different C. immitis isolates.
- The Silveira strain showed notable differences from other California isolates but minimal variation from non-California isolates.
- Only one base substitution impacted the protein sequence across analyzed isolates.
Conclusions:
- The expression pattern of PRA correlates with the protective efficacy of whole-cell vaccines.
- PRA-based diagnostic tests and vaccines are likely to be effective against a broad range of C. immitis isolates.
- Genetic variations in PRA do not significantly compromise its potential as a universal vaccine candidate.
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