CELLULAR AND HUMORAL IMMUNE-RESPONSES IN DOGS EXPERIMENTALLY AND NATURALLY INFECTED WITH LEISHMANIA-INFANTUM

In this paper we describe a number of immunological parameters for dog s with a chronic Leishmania infantum infection which exhibit patterns of progressive disease or apparent resistance. The outcome of infectio n was assessed by isolation of parasites, serum antibody titers to Lei shmania antigen, and development of clinical signs of leishmaniasis. O ur studies show that 3 years after experimental infection, asymptomati c or resistant dogs responded to L. infantum antigen both in lymphocyt e proliferation assays in vitro and in delayed-type hypersensitivity r eaction, whereas no serum antibodies to parasite antigen were shown. I n contrast, symptomatic or susceptible animals failed to respond to pa rasite antigen in cell-mediated assays both in vitro and in vivo and s howed considerably higher serum antibodies to leishmanial antigens. In addition, significantly higher level of interleukin 2 (IL-2) and tumo r necrosis factor were found in supernatants from stimulated periphera l mononuclear cells from asymptomatic dogs compared with those from sy mptomatic and control uninfected dogs. IL-6 production did not vary si gnificantly among the groups studied. Finally, we observed similar res ults with a group of mixed-breed dogs with natural Leishmania infectio ns also grouped as asymptomatic or symptomatic on the basis of clinica l signs of canine visceral leishmaniasis. These results demonstrate th at serum antibody titers, antigen-specific proliferative responses, de layed-type hypersensitivity skin reactions, and IL-2 and tumor necrosi s factor production by peripheral mononuclear cells can be used as mar kers of disease progression.