688 ANTIINFLUENZA HEMAGGLUTININ ANTIBODY DIVERSITY secondary

The initial antibody repertoire is determined by multiple heavy and light chain variable region (V. and VL) ~ gene segments and multiple joining gene segments (J~, Jx, JH, and D.). These gene segments can join in various combinations (1-8) and complete V gene products can associate in different combinations. As a result of combinational joining and association, the size of the preimmune repertoire can in theory be as high as 10 7 different antibodies. This preimmune repertoire is further amplified by junctional diversity that arises by variation at the sites at which gene segments join, and by the addition of nucleotides (N regions) during gene segment joining (9). Somatic mutation may also contribute to the preimmune repertoire, since mutation of the rearranged V gene of a preB cell line has been observed (10). Thus the number of different antibodies in an individual may approach the number of preimmune B lymphocytes. As a result, preimmune B lymphocytes of independent origin can be uniquely defined by the nucleotide sequence coding for their antibody V regions, particularly that of their heavy chain diversity region (DH) and N regions, since these are usually different even in antibodies of the same antigen specificity (11-15). On the other hand, sequence identity in these regions between lymphocytes of a single individual would indicate that they are derived from a single preimmune B lymphocyte. The genotypes of individual lymphocytes are also unique at the unexpressed antibody loci. These silent alleles are often aberrantly rearranged gene segments (H-, ~-, ~-), and hence can be as diverse as the productively rearranged genes (16). In addition, DNA between the VK and JK loci of rearranged L chain genes is often retained. The nature of this upstream (U) DNA depends on which V~ and J, gene segments are joined, hence there is considerable variability in the nature of this upstream DNA (17). As these types of rearrangements occur independently of the productive rearrangements, the context of H-, K-, and U DNA can also uniquely define a given lymphocyte. In this report we describe the V region nucleotide sequence of a number of antihemagglutinin (anti-HA) antibodies generated from BALB/c mice after a