THE EPITOPE ASSOCIATED WITH THE BINDING OF THE CAPSULAR POLYSACCHARIDE OF THE GROUP B MENINGOCOCCUS AND OF ESCHERICHIA COLI KI TO A HUMAN MONOCLONAL MACROGLOBULIN, IgM"°° BY ELVIN A. KABAT,

A human monoclonal macroglobulin IgM"°", has recently been described which has specificity for poly-a(2-"8)-linked N-acetylneuraminic acid (NeuNAc), 1 the specific capsular polysaccharide of the group B meningococcus and of Escherichia coli Kl (1) . Although studies using this polysaccharide as a vaccine in humans have been unsuccessful (2-4, see reference 5), the serum contained over 20 mg of antibody per milliliter. Quantitative precipitin curves of IgM"°" with four preparations, two of group B meningococcal polysaccharide and two ofE. coli Kl were identical (1) . IgM"°" did not precipitate with polysaccharides from group C meningococci composed of poly-a(2-9)NeuNAc nor with E. coli K92 built of alternating a(2-8)a(2-9)NeuNAc, nor with many other polysaccharides . 2 Surprisingly, the polynucleotides poly(A) and poly(I) gave precipitin curves per unit weight identical with those of poly-a(2-8)NeuNAc. Denatured DNA and poly(G) also crossreacted, but about 3 and 12 times as much, respectively, was needed to precipitate comparable amounts of antibody nitrogen (N) from IgM"°"(1) . These crossreactivities would appear to correspond to the findings of Heidelberger (6) who interpreted the extensive crossreaction between types 8 and 19 pneumococcal polysaccharides as due to the negatively charged phosphoryl-Q-D-ManNAc oftype 19 being able to enter the type 8 antibody combining site which is specific for cellobiuronic acid with its carboxyl and vice versa . It was postulated (1) therefore, that the crossreactions with poly(A), poly(I) and denatured DNA could be accounted for by "a similarity in the spatial distribution of charges between the carboxyl groups of poly-a(2-8)NeuNAc and the phosphates of the denatured DNA or poly(A) and poly(I)" (1) .