IMPORTANCE OF
THE IMMUNE RESPONSE

Several factors may affect the body’s response to the parasite, and also the susceptibility or resistance to infection. Firstly, the genetic factor in susceptibility or resistance to the disease is well documented. In the case of the Ibizan Hound, most animals have shown to be resistant to the disease, and very few actually develop it. Some papers suggest that this susceptibility is caused by variants in the Class II Major Histocompatibility Complex (MHC II).

However, the first studies in this field are quite recent and many more variants likely to determine genetic susceptibility or resistance should become known in the future.

Secondly, susceptibility to develop the disease is also influenced by non-genetic factors such as nutritional status, concomitant infections, parasitism and previous exposure to canine leishmaniasis.

While resistance to the disease is associated with the development of cell-mediated immunity, susceptibility is associated with very marked, non-protective humoral immunity and depressed cell-mediated immunity. The latest findings on the pathogenicity of canine leishmaniasis have revealed that protective (cell-mediated) immunity against this disease is mediated by CD4+ T helper 1 (Th1) cell responses.

The cell-related basis of the response, and chiefly the lack of cell-mediated response in canine leishmaniasis, are not fully understood. We do know, however, that the majority of infected dogs initially develop a good cell-mediated immune response. Further on, this response declines with disease progression in susceptible animals.