Methods of treating autoimmune diseases, such as primary immune thrombocytopenia (ITP), solid organ transplant rejection, graft-related disease, pemphigus vulgaris, systemic sclerosis, and myasthenia gravis using antibody polypeptides that specifically bind human CD40L are provided. The antibody polypeptides do not activate platelets. The methods may comprise at least one administration cycle comprising one dose of the antibody polypeptide. The dose may be administered intravenously at a dose from about 75 mg to about 1500 mg. The method normalizes platelet counts in the human patient.