Bovine immune response to papillomatous digital dermatitis (PDD)-associated spirochetes is skewed in isolate reactivity and subclass elicitation

Papillomatous digital dermatitis (PDD) is a growing cause of lameness of dairy cattle worldwide. Farms with PDD-afflicted cows experience economic loss due to treatment costs, decreased milk production, lower reproductive efficiency and premature culling. Cows exhibit both humoral and cellular immune responses to PDD-associated spirochetes. This study was undertaken to further characterize the bovine humoral response to PDD-associated spirochetes. Forty-seven sera samples collected from cattle (Field cattle) on three different dairy operations in Iowa were analyzed. In addition, sera were obtained from six young steers (Test cattle) that received a mixed inoculum of four previously isolated Treponema phagedenis-like spirochetes (1A, 3A, 4A and 5B) on two separate occasions. Relative levels of total IgG, IgG1, IgG2 and IgM reactive to each individual spirochete were determined. Field cattle had a higher mean antibody response to 5B compared to the other isolates and T. phagedenis. Test cattle reacted most strongly with 4A following initial exposure, shifting to a greater reactivity with 5B and a reactivity profile similar to field cattle following secondary exposure. No measurable IgM was detected. IgG1 was produced predominately in all cattle. Low to moderate levels of total IgG reactivity to T. phagedenis occurred with sera from all cattle.