Complement 3 deficiency effects the immune system by a lack of the protein complement component 3 (C3). C3 plays an important role in preventing bacterial infection, and a deficiency results in the body having a greatly reduced immune response, leaving the affected animals susceptible to frequent bacterial infections. Age of onset appears to most commonly be younger dogs, with affected dogs having reoccurring bacterial infections, including pneumonia, urinary tract infections and uterine infections. C3 deficiency predisposes affected dogs to kidney disease early in life, and/or chronic kidney failure.