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From the Department of Microbiology, University of California at San Francisco, San Francisco, California 94122
Abstract
Conditions which favored the production of hemolytically competent C4 sites over incompetent C4 sites on IgM-sensitized cells included a low ratio of Ab:C1 (SA:SAC1 ratio), prior exposure of the EAC1 to 0°C for 30 min or more, and reactive with C4 at 0°C. Other important factors included Ab class, C1 and C4 multiplicity, and the time of incubation. The status of a given C4 site seemed to be set irrevocably at the time C4 first interacted with SAC1, and this status was associated with the affinity with which the C1 was bound to the cell. Cell-bound C1 underwent a completely reversible "super-activation" at 0°C which increased the proportion of hemolytically competent C4 sites generated during subsequent interaction with C4. The configuration of a C1 molecule, as determined by the affinity with which it is bound to a cell, may determine the hemolytic competence of a C4 molecule reacting with that site.
Footnotes
1 This work was supported by American Cancer Society Grant E-529.
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