Immunoglobulin isotype distribution of antinuclear antibodies in dogs withleishmaniasis

A modified indirect immunofluorescence method, using rat liver as substrate , was developed to determine the immunoglobulin isotypes forming antinuclea r antibodies in sera from 12 antinuclear antibody-positive dogs out of 121 dogs with natural Leishmania infection. Immunoglobulin M was found to be th e most frequent component of antinuclear antibodies (91.7 per cent), follow ed by IgG (41.7 per cent) and IgA (33.2 per cent). When these immunoglobuli n isotypes were titrated, IgG antinuclear antibodies showed higher titres ( 1:200) than IgM and IgA antinuclear antibodies (1:50 and 1:20 respectively) . Most of the antinuclear antibody-positive dogs simultaneously had two imm unoglobulin isotypes, whereas none had all three immunoglobulin isotypes at the same time. Spearman rank correlation analysis showed no significant co rrelation between antinuclear antibody titres and circulating immune comple xes or immunoglobulin levels. The low incidence of antinuclear antibodies a nd the absence of a clear relationship between isotype titres and clinical signs suggest a minor pathogenic role of antinuclear antibodies in canine l eishmaniasis.