DIVERSITY OF IMMUNOGLOBULIN LIGHT CHAIN USAGE IN THE HUMAN IMMUNE-RESPONSE TO HAEMOPHILUS-INFLUENZAE TYPE-B CAPSULAR POLYSACCHARIDE

The response to the capsular polysaccharide of Haemophilus influenzae type b (Hib PS) has been used to determine the molecular basis of antibody gene diversity in humans. In contrast to the relatively restricted nature of anti-Hib PS heavy-chain variable region gene expression, a variety of light-chain variable region genes may encode this antibody (Ab) response. Light-chain variable region gene usage appears to determine the expression of certain Ab idiotypes and fine antigen specificity. To further define the role of light-chain variable region gene usage in important anti-Hib PS Ab subgroups, we have cloned and sequenced a number of immunoglobulin light-chain variable region genes (IgVL) from human monoclonal IgA anti-Hib PS Ab generated in response to Hib PS-protein conjugate vaccines. Three of these Ab are encoded by unusual variable segments. One kappa-Ab is encoded by the ''predominant'' VkappaII A2 germline gene but, in contrast to a previously reported A2-encoded IgVL sequence, differs from the A2 germline sequence. The IgVL sequence of a second Ab is the only sequence of a kappa-Ab that cross-reacts with the structurally related antigen Escherichia coli K100 polysaccharide reported to date. This IgVL is encoded by a VkappaIII-segment most closely homologous to the Humhv328/L16 germline gene, whereas previous reports suggested VkappaIII encoded anti-Hib PS Ab might be exclusively encoded by the germline gene Humhv325/A27. A lambda-Ab, also cross-reactive with K100 polysaccharide, is encoded by a VlambdaIII family member, in contrast to our previous report of four lambda-Ab with similar antigen specificity that appeared to be encoded by a single VlambdaVII-gene family member. Each of the three Ab reported here contain an arginine codon at the VJ joint, indicating an important role in antigen binding. Our data indicate, in marked contrast to the restricted nature of the heavy-chain anti-Hib PS repertoire, a much greater diversity in light-chain variable gene segment usage.