Immunoglobulin variable region gene expression in response to Haemophilus influenzae type b polysaccharide

The mechanism(s) responsible for the ontogenic patterns of acquisition of the antibody repertoire is unknown. The immune response to Haemophilus influenzae type b (Hib) capsular polysaccharide provides an excellent model system in which to examine the ontogeny of immunoglobulin variable region expression. A panel of hybridomas secreting human antibodies specific for Hib capsular polysaccharide was developed using peripheral blood lymphocytes from donors immunized with Hib vaccines. Nucleotide sequence analysis of the heavy chain V regions expressed by four of these hybridomas suggests selective use of members of the VHIII gene family in combination with different D and J segments. The nucleotide sequences were highly homologous to two candidate germline gene sequences. Others have reported that these particular germline sequences are expressed in fetal liver, suggesting that the inability of young children to produce antibody to the Hib capsular polysaccharide is not due to failure to express these VH regions early in ontogeny.