Immunophenotype and cytokine production of canine lymphocytes

Expanding current knowledge of canine immunity is beneficial to the use of dogs as natural animal research models and for the translation of human treatment regimes to veterinary medicine. ELISAs (enzyme linked immunosorbent assay) were developed for detection of canine IL-2, IL-4, IL-5, IL-10, IFN-gamma and TNF-alpha in cell supernatants from canine lymphocytes cultured in the presence of common pathogens (canine distemper virus [CDV), Malassezia and Toxocara canis) of dogs to determine if they would induce Th1/Th2 type responses. The pattern of cytokine production elicited by these antigens did not fit classical Th1 or Th2 responses, except in the case of Toxocara canis where a clear bias to IL-5 production, and therefore a Th2 response, occurred early. It could not be determined whether lack of an inflammatory Th1 cytokine response to CDV and Malassezia in vitro was a function of the assay system or a true indication of what would occur in vivo. IL-4 production in response to Malassezia was age-associated such that older dogs (≥ 4 years) had a tendency toward higher IL-4 production than young dogs. The balance of Th1 versus Th2 cytokine production shifted significantly over time demonstrating the dynamic nature of this cell cross-talk system. It is anticipated that in vivo responses would be even more complicated. Invariant natural killer T (iNKT) cells are important regulators of immune responses to bacterial, viral and parasitic infections and play an important role in self-tolerance and tumor surveillance. To determine if dogs have iNKT cells, a human CD1d tetramer loaded with the glycolipid PBS57 was used to identify iNKT cells within the CD3+ population of canine blood and liver using flow cytometry. A small proportion of CD3+ CD1d tetramer-binding cells were present in the lymphocyte gate of blood (0.012%) and liver (0.074%). This proportion of iNKT cells is similar to what is observed in normal human tissues but much lower than in mice. In summary, findings from these studies support the position that the dog is immunologically very similar to man and is a natural model for the study of human immune-mediated diseases.