CLINICAL IMMUNOLOGY AND IMMUNOPATHOLOGY 23, 297-311 (1982) Detection and Analysis of Inborn and Acquired Complement Abnormalities* ANITA T. GEWURZ, THOMAS F. LINT, SUZANNE M. IMHERR, SARAH S. GARBER, AND HENRY GEWURZ Departmenf of Immunology/Microbiology, Rush Medical College, Chicago, Illinois 60612 Multiple inborn and acquired abnormalities of the complement system have been observed in man, frequently in association with autoimmune, infectious, and inflamma- tory disease processes. Since hemolytic activity mediated by the classical and alternative pathways can be measured by utilization of sensitized sheep and unsensitized rabbit erythrocytes, respectively, we have implemented an approach for the rapid, convenient identification of C abnormalities utilizing hemolytic reactions in agarose gels to select or exclude samples for further study. Sera with normal hemolytic activity were readily identified, as were sera (lo- 15% of those in which C assays were requested of the routine laboratory) in which more detailed analysis was desirable. Sera totally deficient in an early acting component of the classical C pathway (Cl, C4, C2) were apparent by selective hemolysis, while sera lacking a terminal component other than C9 failed to induce hemolysis in either system. Individual component defects were easily identi- fied in deficient sera by specific hemolytic reconstitution following addition of the miss- ing component using commercially available reagents, or by combination with appropri- ate C-deficient sera. Despite its semiquantitative nature, hemolysis in gel screening, together with C4 and C3 protein levels, provided rapid and useful categorization and definition of inborn and acquired C abnormalities, including detection of 17 kindreds with individuals having complete deficiency of a C component. INTRODUCTION An improved understanding of immunologic mechanisms and their role in host defense has been generated by the study of the immunodeficiency diseases as “experiments of nature,” the importance of which Robert A. Good has empha- sized (l-3). Of these, deficiencies of human complement (C) comprise a signifi- cant portion and have helped reveal information about the structure, function, and genetics of the C system and of its role in disease (4- 11). Patients with acquired abnormalities of the C system also have been studied in attempts to understand the biological role of C in health and disease (4,5, 1 1 - 14). To detect patients with abnormalities of C, we have utilized hemolytic gel techniques, that have identified over 22 new cases of total C deficiency. These procedures involve the radial diffusion of serum C from wells into buffered agarose suspensions of erythrocytes (E), which activate and indicate lysis via the classical (15) and alternative (16) C pathways when sensitized sheep E (ShEA) and nonsensitized rabbit E (RaE), respectively, are used. In this report we describe and evaluate our experience using ShEA and RaE hemolytic plates to estimate levels of classical and altema- tive pathway C and to identify and classify functional C defects. We also present a new method for the rapid presumptive identification of inborn errors of C, by reconstitution in gel plates of the deficient C activity. This approach provides a x This article is dedicated to Robert A. Good on the occasion of his 60th birthday. 297 0090-1229/82/050297-15$01.00/O Copyright @ 1982 by Academic Press. Inc. All rights of reproduction in any form reserved.