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Comparison of Aa1 Allotypic Specificity Carried by Rabbit IgG and IgM¹

From the College of Veterinary Medicine, University of Illinois, Urbana, Illinois 61801 and the Department of Microbiology, University of Georgia, Athens, Georgia 30601

Abstract

Sheep red blood cells (RBC) sensitized with a sub-hemolytic dose of anti-sheep RBC IgG of a1, b4 allotypic specificity did not hemolyze upon addition of complement, but hemolyzed upon successive treatment with anti-a1 serum and complement. When sheep RBC so sensitized were incubated in agar together with spleen cells from an a3, b4 rabbit which had been immunized with a1, b4 IgG, hemolytic, complement-dependent plaques appeared around cells secreting anti-a1 antibodies. Plaques were specifically inhibited by Ig bearing the a1 allotypic specificity. Thus, it was possible to compare a1 IgG with a1 IgM for efficiency of plaque inhibition. The molar concentration of IgG required to inhibit 50% of the plaques was about 27-fold smaller than the corresponding concentration of IgM (calculated on the basis of the molecular weight of the subunit), showing that antibody produced by single cells had greater average affinity for the immunizing IgG than for the cross-reacting IgM. As IgM, used in sufficient concentration, caused 100% plaque inhibition, there was no evidence of cells producing antibody specific for a determinant present only on IgG. All experiments were done with a single batch of immune spleen cells, which were preserved in liquid nitrogen.

Footnotes

This work was supported by Contract Nonr-1834 (37) from the Office of Naval Research (principal investigator: D. Segre), by Contract COO-1628-7 from the United States Atomic Energy Commission (principal investigator: D. Segre) and by National Science Foundation Grant GB-5551 (principal investigator: F. P. Inman). In addition, Dr. Inman received partial support from the Institute of Comparative Medicine of the University of Georgia.

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