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Production of Antiserum to Human Properdin and Demonstration of Antigenic Differences between the Native and Activated Protein 1

Summary Antisera were raised in rabbits to human properdin in the precursor form (P) and in the activated state (P). On Ouchterlony analysis using the anti-P, reactions of complete identity were obtained between P, P, and properdin in twofold concentrated serum (NHS). However, when anit-P was used, a reaction of identity was obtained only between P and NHS, and a reaction of partial identity was formed between P and P and between properdin in NHS and P, suggestive of the fact that certain antigenic determinants in P may be lacking in P. The results indicate that activation of precursor properdin may involve proteolytic cleavage and/or conformational alterations of the molecule. The author thanks Miss E. Kunar and Miss D. Mann for their valuable technical assistance, and Dr. D. M. Wrobel and Mrs. I. Macdonald of the Canadian Red Cross Society for a generous supply of blood.