Differences in the antigen structures of Corynebacterium pseudotuberculosis and the induced humoral immune response in sheep and goats.

Caseous lymphadenitis (CLA), a disease affecting sheep and goats, is caused by Corynebacterium pseudotuberculosis (Cp). Eradication programs are based on the serological identification of Cp infected animals. However, available diagnostic ELISAs are not similarly suitable for sheep and goats. In the present study the comparison of antigens revealed major species specific differences between sheep and goat derived Cp field isolates as well as between field isolates and the Cp ATCC reference strains. Furthermore, we found species-specific differences in the anti-Cp humoral immune response between sheep and goats. The analysis of band frequency was able to distinguish between immunodominant and non-immunodominant protein bands. The 150 kDa, 74 kDa, 48 kDa, and 30 kDa antigens were immunodominant in both, sheep and goats. Interestingly, the most commonly used diagnostic antigen, i.e. the 30 kDa phospholipase D (PLD), was recognized by 100% of the Cp positive goats but only by 70% of the Cp positive sheep. Furthermore, analysis of field sera revealed that there were a particular percentage of Cp positive sera which reacted negative with the PLD. In conclusion our results clearly showed that (1) the application of a combination of further defined immunodominant Cp antigens - in addition to the PLD antigen - and (2) consideration of species-specific differences in the anti-Cp immune response will substantially contribute to the improvement of Cp serological diagnostics and to effective eradication programs in both sheep and goats.