Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 12, 2000
Publication Date: N/A
Leukotoxin (Lkt) from Pasteurella haemolytica has been shown to bind to the Beta2 integrin receptor LFA-1 and subsequently initiate a cascade of signaling events leading to activation and lysis of target cells. Post- translational modification of pro-Lkt by the product of the LktC gene is considered a pre-requisite for its unique specificity and biological activity. Specific domains of the native toxin are believed to have uniqu roles in interaction with target cells. The objectives of this study were to investigate two allelic replacement mutants, one lacking 64 amino acid residues in the LktC protein and one lacking 344 amino acid residues in the N-terminal region of the structural protein LktA, in regard to cell binding, signaling, and function. The results of our Lkt binding experiments demonstrated that both mutant Lkts bind to the LFA-1 receptor on target cells. No significant cytolysis with either mutant Lkt was observed using an LDH release assay. Neither mutant elicited an elevation in intracellular calcium, which was taken as evidence that neither elicit signaling within the target cell. However, both mutant Lkts demonstrated the ability to abrogate the calcium response in target cells, albeit to varying degrees, caused by native Lkt. In conclusion, our results indicate that the entire Lkt gene product and its normal post-translational modification are pre-requisites for functional activity against target cells. Furthermore, binding per se to the LFA-1 receptor appears to be insufficient to induce the signaling cascade leading to biological activity.