Corynebacterium pseudotuberculosis secreted antigen-induced specific gamma-interferon production by peripheral blood leukocytes: potential diagnostic marker for caseous lymphadenitis in sheep and goats.

In the current study, the applicability of the quantification of gamma interferon (IFN-γ) levels for the detection of animals infected with Corynebacterium pseudotuberculosis and for determining caseous lymphadenitis (CLA) clinical status was evaluated. Peripheral blood leukocytes were collected from CLA nonendemic areas animals, from CLA seropositive animals without clinical signs of the disease, and from seropositive animals presenting CLA clinical signs. The leukocytes were stimulated with C. pseudotuberculosis-secreted antigens that were concentrated by the three-phase partitioning technique. An ovine IFN-γ enzyme-linked immunosorbent assay was used to quantify IFN-γ production. Goats and sheep with CLA had higher IFN-γ levels than uninfected seronegative animals. Leukocytes from sheep with CLA chronic abscesses produced higher IFN-γ levels when compared with seropositive sheep without CLA clinical signs, but this difference was not significant in goats. The sensitivity of the assay was 55.8% and 56%, whereas the specificity was 100% and 93%, for goats and sheep, respectively. In conclusion, IFN-γ is a potential marker for the determination of CLA infection status in small ruminants; however, further research is needed to improve assay sensitivity.