Thyroid humoral autoimmunity in the dog

Humoral autoimmunity, in particular the production of autoantibodies to thyroid antigens, is associated with the development of thyroid disease in both dog and man. This study has examined methods for the detection of thyroid autoantibodies in dogs, the prevalence of these antibodies in dogs with and without thyroid disease, and the experimental induction of thyroid autoimmunity in a group of dogs. Additionally, the occurrence of another organ specific autoantibody, directed against beta cells of the pancreatic islet, was examined in dogs with thyroid and other endocrine diseases. Autoantibodies to thyroid antigens were detected in serums from 34 clinically hypothyroid dogs by a variety of methods. Antibodies to thyroglobulin were detectable by enzyme-linked immunosorbent assay (ELISA) in 59%, by chromic chloride hemagglutination in 53% and by indirect immunofluorescence on formalin-fixed paraffin-embedded trypsindigested tissue in 73% of serums. Antibody to microsomal antigen was detected in 29% of samples by ELISA. The other methods examined were unsuitable due to low sensitivity, excessive tissue fragility or unreliabi1ity. ELISA was also used to examine the occurrence of autoantibodies to thyroglobulin in dogs without clinical thyroid disease. Autoantibodies were found in 43% of 65 dogs with nonthyroidal endocrine diseases, 47% of 64 healthy dogs closely related to antibody positive hospital patients and 13% of 1057 hospital patients without endocrine disorders. A significantly increased prevalence of autoantibodies was demonstrated in dogs with bacterial skin diseases, alopecias of unknown etiology, and within some breeds and in particular within some families of dogs. Total thyroxine levels were similar in antibody positive and antibody negative dogs. Pancreatic islet cell cytoplasmic autoantibody was detected by indirect immunofluorescence. The highest proportion of positive dogs were those with diabetes mellitus (22/35); however, dogs with other endocrine abnormalities, including 6/28 dogs with hypothyroidism, were also antibody positive. Experimental thyroid autoimmunity was induced in six dogs by the parenteral administration of thyroid extract in complete Freund's adjuvant. Autoantibodies were readily induced in all dogs and in four dogs were accompanied by pathological changes in thyroid gland biopsies. Thyroxine levels fell to below normal levels in five dogs; however, this was associated with pathological changes in the thyroid biopsy in only one dog. Fixed immunoglobulin was not demonstrable in biopsy tissues by indirect immunofluorescence