The crystal structure of Fab R19.9, derived from an anti-p-azobenzenearsonate monoclonal antibody, has been determined and refined to 2.8-A resolution by x-ray crystallographic techniques. Monoclonal antibody R19.9 (IgG2bK) shares some idiotopes with a major idiotype (CRIA) associated with A/J anti-p-azobenzenearsonate antibodies.The amino acid sequences of the variable (V) parts of the heavy (VH) and light (VL) polypeptide chains of monoclonal antibody R19.9 were determined through nucleotide sequencing of their mRNAs. The VL region is very similar to that of CRIA-positive anti-p-azobenzenearsonate antibodies as is VH, except for its third complementarity-determining region, which is three amino acids longer; it makes a loop, unique to R19.9, that protrudes into the solvent. A large number of tyrosine residues in the complementarity-determining region of VH and VL, with their side chains pointing towards the solvent, may have an important function in antigen binding. Murine antibodies to model antigens have provided valuable experimental systems to study the molecular bases of the specificity, diversity, and genetic control of immune responses. The hapten, p-azobenzenearsonate (Ar), has been used in several laboratories as a suitable probe for such studies (1-5), which have been facilitated by the presence of an intrastrain cross-reactive idiotype, designated CRIA, among the anti-Ar antibodies of A/J mice or ofclosely related strains. The expression of CRIA is linked to genetic loci encoding heavy (H) chains (6) and light (L) chains (7). On the average, about half of the anti-Ar antibodies induced by keyhole limpet hemocyanin-Ar in A/J mice share this idiotype. The variable (V) regions, VH and VL, of CRIA antibodies appear to be encoded by single germ-line genes (8,9), and the diversity (D) region is encoded by a variant of the DFL16.1 gene (10). CRIA molecules also utilize the VK10, K chain joining (J) 1, and, almost invariably, JH2 gene segments (4, 5, 11). Idiotypeexpressing antibodies from hyperimmunized mice display somatic variants ofamino acid sequences in each ofthese gene segments (4, 5, 12), whereas the antibodies from an early primary response reflect few if any mutations (5). The VH region appears to be somewhat more susceptible to somatic variation than VL (4). A disproportionate number of mutations in VH and VL occurs in their complementarity-determining regions (CDR); this probably reflects selection by antigen of variants with higher affinity (5).Among the serum anti-Ar antibodies of immunized A/J mice are molecules that carry some but not all ofthe idiotopes associated with CRIA (13,14). Such antibodies are bound by anti-CRIA antibodies, but they are unable to completely displace labeled CRI+ antibodies from such anti-idiotype antibodies. Antibodies of this type were designated "minor idiotypes" (13,14). The subject of the present investigation, monoclonal antibody (mAb) R19.9 (IgG2bK), has these serological properties and is thus a member of a minor idiotypic anti-Ar family. The ...

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Hepatitis A virus (HAV) has an immunodominant neutralization antigenic site. By using a panel of monoclonal antibodies targeted against the HAV neutralization antigenic site, it was shown that three epitopes within this site are present on 14S subunits (pentamers of the structural unit). In contrast, two other epitopes within this site are formed upon assembly of 14S subunits into capsids. Thus, the epitopes recognized by these two monoclonal antibodies are formed either by a conformational change in the antigenic site or by the juxtaposition of epitope fragments present on different 14S subunits during assembly of 14S into 70S particles. Both 14S and 70S particles elicited HAV-neutralizing antibodies in mice; thus, these particles may be useful for HAV vaccine development.

We describe here an intrastrain, cross-reactive idiotype (CRI), CRID, associated with anti-p-azobenzenearsonate antibodies of the A/J strain of mouse and distinguishable, by some but not by all of its idiotopes, from the major anti-p-azobenzenearsonate idiotype (CRIA). Molecules carrying the CRID idiotype have heavy chain variable-segment sequences that are identical or nearly identical to that of the germ-line-encoded heavy chain variable sequence of CRIA. Their light chain variable sequences are very similar to those present in a third idiotypic family, CRIc, that is a minor CRI in the A/J strain but a major CRl in BALB/c. This appears to represent a form of combinational diversity, in which the heavy and light chain variable region genes of two unrelated idiotypic families interact to form a third family, all involving antibodies of the same antigen-binding (anti-p-azobenzenearsonate) specificity. The D region of CRID, in the six monoclonal representatives studied (three IgMs, three IgGs), is unusual in that it comprises a single amino acid-arginine or serine; there are eight amino acids in the D region of CRIZ antibodies. Three different heavy chain joining regions, JH1, JH2, and JH3, are utilized. A serological reagent was developed that identifies CRID; it was used to show that the idiotype is present in relatively high concentration, comparable to that of CRIA, in anti-p-azobenzenearsonate antibodies taken soon after primary immunization. In serum taken later CRIA greatly predominates, but CRID persists at low levels.An average of about half the anti-p-azobenzenearsonate (anti-Ar) antibodies of hyperimmunized A/J mice share an intrastrain cross-reactive idiotype (CRI), designated CRIA. The expression of CRIA is linked to the Ighe locus, that encodes the heavy chains of immunoglobulins in this strain (1). Linkage to genes controlling K chains has also been demonstrated (2). It was proposed that the recurrence of this idiotype (Id) is caused by its association with one or a small number of germ-line genes (3) and that nonrecurrent, or private idiotypes, which constitute a large proportion of the late anti-Ar response, arise through somatic mutation of germ-line genes (4). Direct evidence that the heavy chain variable (VH) segment (positions 1-98) of CRI' antibodies is encoded by a germ-line gene was reported by Siekevitz et al. (5). Evidence that the light chain variable (VL) region is similarly encoded by a germ-line gene is indirect but strong; it is based on the striking conservation of VL amino acid sequences in individual CRII monoclonal antibodies (mAb) (refs. 6 and 7; E.M.R., unpublished results).In this paper we describe the properties of another intrastrain CRI, designated CRID, also associated with A/J anti-Ar antibodies. Its prevalence, relative to that of other anti-Ar antibodies, is highest early after immunization, but the idiotype persists at low levels in hyperimmunized animals. The unique structural features of CRID are discussed in terms of the mechanisms controlling the antibody...