EXPRESSION OF EQUIVALENT CLONOTYPES IN BALB/c AND A/J MICE AFTER IMMUNIZATION WITH PHOSPHORYLCHOLINE BY STUART RUDIKOFF AND J. LATHAM CLAFLIN*

A series of phosphorylcholine (PC) 1 binding myeloma proteins of BALB/c origin have been described and characterized by several laboratories (1-4). One group of these proteins, including among others T15, H8, and S107, has been shown to possess identical variable region antigenic determinants (idiotypes) (2, 5) as well as identical partial variable region light and heavy chain amino acid sequences (6). This group of proteins also demonstrates the same binding specificity for PC and various analogs (3). Other PC binding proteins have been identified (M603, M167, Mfll , and W3207) which have different idiotypes (2, 4), variable region amino acid sequences (6-10), and specificity (3, 11). Studies in this laboratory and others (5, 11-14) have suggested that BALB/c mice immunized with PC-containing antigens respond by making antibodies predominantly of the T15 idiotype. We have further shown that rabbit antisera specific for an idiotypic determinant(s) in or associated with the combining site of the T15 group recognizes the same determinant in antibodies to PC elicited in BALB/c and 17 other mouse strains (5), suggesting a conservation in this species of at least one binding site for PC. The characterization of a PC-binding myeloma protein in CB 20 mice (BALB/c. B6 [IgCH]) with structural, functional, and idiotypic characteristics similar to T15 (15) further supports this contention.