Resumo

This study aimed to investigate the association of the acute phase response with the outcomes (presence or absence of lesions) of sheep caseous lymphadenitis (CLA) during primary infection and in animals immunized with a saponin-adjuvanted immunogen. Fifteen sheep were used in this investigation, which were divided among Group 1 (Control), Group 2 (experimentally infected) and Group 3 (immunized with Corynebacterium pseudotuberculosis (Cp) secreted antigens adjuvanted with Quillaja saponaria saponins). The acute phase period was monitored for 21 days through levels of IgM and the acute phase protein haptoglobin (Hp), but animals were observed until the 182nd day and slaughtered to investigate internal CLA lesions. The primarily infected sheep in Group 2 presented higher (p<0.05) Hp values between the 1st and 9th days post inoculation (PI), in comparison to Group 1 (Control); however, the immunized animals in Group 3 presented the significantly highest (p<0.01) Hp values between the 3rd and 7th days PI when compared to control group. A binary logistic regression (BLR) analysis for Group 2 indicated an association between Hp concentration and CLA outcome, in which the animal with high Hp values had 99.9% less risk (Odds ratio=0.001, p<0.05) of having CLA abscesses than animals with low Hp levels. Concerning IgM antibodies, both experimental groups presented significantly higher (p<0.05) titres around the 9th and 11th days PI when compared with the control group; the BLR analysis for Group 3 indicated an association between IgM and outcomes, in which sheep with high IgM titres had 100.0% less risk (Odds ratio=0.000, p<0.05) of having CLA abscesses than animals with low IgM levels. The resistance to Cp infection is supported by the early activated acute phase response, in which the up-regulation of Hp and IgM were predictive of a less risk of having CLA lesions. Since the immunogen used in the study was able to induce the high production of both Hp and IgM, the Q. saponaria saponins should be considered promising candidates for composing the next vaccine models against sheep CLA.