Sequence diversity of the immunogenic outer membrane lipoprotein PlpE from Mannheimia haemolytica serotypes 1, 2, and...

Area of Science:

• Veterinary immunology
• Bacterial genomics
• Livestock disease research

Background:

• Shipping fever pneumonia in beef cattle is commonly caused by Mannheimia haemolytica serotypes 1, S6, and S2.
• Current vaccines offer incomplete protection, highlighting the need for improved immunogens.
• Outer membrane proteins (OMPs) of M. haemolytica, particularly PlpE from serotype 1, show promise for enhancing immunity.

Purpose of the Study:

• To investigate the conservation of the PlpE gene, specifically the immunodominant R2 epitope, across different M. haemolytica serotypes.
• To assess the potential of the PlpE R2 epitope as a vaccine candidate for broad-spectrum protection against shipping fever pneumonia.

Main Methods:

• Sequencing of the plpE gene from 32 M. haemolytica isolates representing serotypes S1, S6, and S2.
• Analysis of sequence variation, particularly in the hexapeptide repeat region of the R2 epitope.
• Western blot and competitive binding assays to compare PlpE protein expression and antibody binding across serotypes.

Main Results:

• The plpE gene sequences were identical between serotypes S1 and S6, with minor exceptions.
• Significant variation in the R2 region of PlpE was observed in serotype S2 isolates, with repeat numbers ranging from 3 to 28.
• PlpE molecular weights varied from 30 to 50 kDa in S2 strains, compared to 37 kDa in S1 and S6 strains.
• Antibodies against recombinant PlpE from S1 bound native PlpE on both S1 and S2 M. haemolytica cells.

Conclusions:

• The variability of the PlpE R2 epitope in M. haemolytica serotype S2 strains may limit its efficacy as a universal vaccine component.
• Despite sequence variation, antibodies to PlpE from serotype S1 demonstrate cross-reactivity with PlpE from serotype S2, suggesting potential for broader immunity.
• Further research into conserved epitopes or alternative vaccine strategies is warranted for comprehensive protection against shipping fever pneumonia.