1 Institute of Innovation for Agricultural Production and Sustainable Development (IPADS), Argentina; 2 College of Agricultural Sciences, National University of Mar Del Plata, Balcarce, 7620 Argentina; 3 National Institute of Agrarian Technology (INTA), Buenos Aires, Argentina; 4 Faculty of Veterinary Sciences, National University of the Center of Buenos Aires, Tandil, 7000, Argentina; 5 Immunoparasitology Laboratory, Faculty of Veterinary Medicine, National University of La Plata, La Plata, Argentina; 6 Instituto De Agrobiotecnología y Biología Molecular (IABIMO) INTA - CONICET, Castelar B1712WAA, Argentina; 7 Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Canada.
Delayed-type hypersensitivity (DTH) has been used in human and veterinary medicine as a skin testing for evaluating in vivo cell-mediated immune responses (CMIR). Whereas CMIR is a key process to control intracellular pathogens, its value at identifying cattle exposed to the abortigenic intracellular coccidian parasite Neospora caninum is unknown. In this work, we have evaluated a DTH skin testing in cattle exposed to N. caninum and still seronegative. Female calves were experimentally sensitized by subcutaneous (SC) inoculation with live tachyzoites of N. caninum (NC-Argentina LP1) in sterile phosphate-buffered saline (PBS) (group A; n: 8) whereas other calveswere mock-sensitized with PBS (group B; n: 6). Two DTH skin tests were performed by intradermal inoculation with a soluble lysate of N. caninum tachyzoites (NC-Argentina LP1) in the neck region at 60d and 960 d after sensitization. Skinfold thickness at the intradermal inoculation site was measured at 0, 24, 48 h post each DTH skin test and skin biopsies taken for microscopic evaluation. Specific N. caninum antibodies kinetics was evaluated all throughthe experiment. We found that whereas N. caninum specific antibodies remained below the ELISA cut-off, a distinctive skinfold thickness increase was detected in sensitized animals (group A) at the DTH skin test site, showing induration, swelling and inflammatory infiltration. Mock sensitized animals (group B) showed no skinfold thickness growth and lacked specific antibody response. Thus, N. caninum DTH skin testing could be a useful diagnostic tool for the detection of CMIR during N. caninum infection in non-humoral responders.
Keywords: Neospora caninum, Delayed type hypersensitivity, Cell-Mediated immune response, Skin test, Cattle.
Abstract published in Comparative Immunology, Microbiology and Infectious Diseases, Volume 72, October 2020, 101522. https://doi.org/10.1016/j.cimid.2020.101522.