The clinical manifestations of a genetically determined deficiency of the third component of complement in the dog.

The clinical manifestations of a genetically determined deficiency of C3 were examined in a closed colony of dogs. One hundred and twelve dogs, including twenty C3-deficient dogs, were studied over a period of 6 years. Five of the C3-deficient dogs developed significant bacterial infections, such as pneumonia, sepsis, and pyometra, which were caused by Clostridium spp., Escherichia coli, and Klebsiella spp. Two of the C3-deficient dogs who had had significant infections also subsequently developed renal disease. Secondary amyloidosis was the predominant renal lesion in one dog. The predominant renal lesion in the second dog was membranoproliferative glomerulonephritis, although some amyloid was also present. The two dogs with renal disease also had positive rheumatoid factors. No other clinical or serological evidence of autoimmune disease or immune complex disease has been found. None of the dogs heterozygous for C3 deficiency, and none of the homozygous normal dogs in the colony has developed significant bacterial infections or renal disease. Thus, dogs deficient in C3, like C3-deficient humans, demonstrate both an increased susceptibility to infection and renal disease.