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Agglutinating Activity of the Complement Component C'1q in the F-II Latex Fixation Test¹

From the Division of Arthritis, University of Maryland, School of Medicine, Baltimore, Maryland

Abstract

Native human serum treated with Na₃H-ethylenediaminetetracetic acid (EDTA) exerts strong agglutinating activity in a modified F-II LP test. A study for the identification of the agglutinating principle revealed:

1. Agglutinating activity found in 14.5% of 110 native sera was enhanced significantly following treatment with Na₃H-EDTA. In 94 (85.5%) sera originally negative in this test high agglutinating titers emerged following Ca⁺⁺ depletion.

2. The agglutinating factor is thermolabile.

3. Ultracentrifugation of native sera resulted in concentration of the factor in the pellet, suggesting its migration with heavy molecules. Na₃H-EDTA treatment prior to centrifugation prevented concentration while agglutinating activity remained in the supernatant, indicating that Ca⁺⁺ depletion may have resulted in the dissociation of the molecule naturally associated with the factor.

4. Selective absorption of the C'1q (11S) component of serum complement resulted in disappearance of agglutinating activity.

5. A semi-purified preparation of C'1q caused agglutination in this system. Agglutination titers depended on the concentration of C'1q.

Conclusion. The characteristics of the agglutinating factor described in this article resemble those of the C'1q (11S) component of human complement.

Footnotes

¹ Grants in support of these investigations have been received from the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, United States Public Health Service (Grants 2A-5059 and AM-03173) and from The Arthritis Foundation.