Anti-Leishmania humoral and cellular immune responses in naturally infected symptomatic and asymptomatic dogs

Canine infections with Leishmania infantum represent a considerable veterinary medical and public health problem. In this study, immunoglobulin GI (IgG1) and IgG2 specific Immoral responses were measured and compared with the delayed type hypersensitivity (DTH) cellular response to a leishmanin, in three groups of dogs clinically and serologically characterised as: (I) asymptomatic and direct agglutination test (DAT)-seronegative; (II) asymptomatic and DAT seropositive; (III) DAT-seropositive and symptomatic. IgG2 was regarded as a marker of disease, since significantly higher levels of this subclass were recorded in the symptomatic dogs. In contrast, the IgG1 response could not be related to clinically relevant infection. A high correlation was observed between IaG2 level and DAT titre; the correlations between IgG1 and IgG2 levels, and between IgG1 level and DAT titre were lower. This may indicate that IgG2 is the main subclass in the specific Immoral response which is detected by the DAT. A reduced IgG2 response, albeit not significantly different, was recorded among dogs with clear cellular immune responses detected by a DTH positive reaction. Furthermore, no correlations were observed between cellular response measured by DTH and Immoral responses quantified by DAT titre or IgG1 and IgG2 levels. Combining serology and DTH skin test is a practical procedure to assess anti-Leishmania immune responses in dogs. (C) 2007 Elsevier B.V. All rights reserved.