Isofixation Curves As a Method of Standardizing Quantitative Complement-Fixation Tests

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Abstract
The purpose of the present report is to call attention to the “isofixation curves,” which can be constructed from a box titration of serum and antigen in the presence of fixed amounts of complement, and the value such curves may have in defining the relationships between antigen and antibody in a variety of complement-fixation systems. The principles have been implicit in earlier work1 but their full usefulness may be greater than has been appreciated. Materials and Methods. Sera. The sera used in each test are indicated in the figures. Sera were inactivated at 56°C for 30 min and dilutions were made in normal pooled sera or saline. Antigens. The antigens were prepared according to specifications given elsewhere (2–12). Dilutions were made in borate salt solution, pH 7.6 (13). Complement. Pooled guinea pig sera titrated in 50% hemolytic units with maximally sensitized sheep cells were used.
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