Limited sequence variation in the major sperm protein 1 (MSP) gene within populations and species of the genus Dictyocaulus (Nematoda)

Populations of the bovine lungworm, Dictyocaulus viviparus, are genetically structured based on variation in mtDNA and AFLP data. Our aim was to investigate if this genetic variability also is reflected in a protein recognized by the host immune system. We focused on the major sperm protein (MSP), a small and abundant protein used in diagnostic immunoassays, which has been shown to be variable in some nematodes but not others. MSP was sequenced using worm DNA from eight adult worms from each of nine populations whose genetic structure previously had been quantified. For comparison, we also analyzed MSP sequences of the closely related Dictyocaulus eckerti and Dictyocaulus capreolus and from nematodes with sequences deposited in GenBank. In contrast to previous results, this study shows that the MSP of D. viviparus is similar to that of other nematodes. Almost no sequence variation, and thus no antigenic diversity, was detected in MSP between worms from different sub-populations or in the other Dictyocaulus species investigated. A functional test of a recombinant variant of the MSP showed that the expressed protein was recognized by antibodies in sera from infected cattle. This has practical implications for the development of species-specific markers, recombinant vaccines, and immunodiagnostics.