IGH V3-23*01 and its allele V3-23*03 differ in their capacity to form the canonical human antibody combining site specific for the capsular polysaccharide of Haemophilus influenzae type b.

The IGH V3-2301 gene is used in the formation of the canonical combining site which dominates the human antibody repertoire to the Haemophilus influenzae type b (Hib) polysaccharide (PS). An allele of the human IGH V3-2301 gene, known as V3-2303, differs from V3-2301 in nine bases, eight of which are located in the second complementarity determining region. These eight differences encode five amino acid substitutions. In this study we investigated whether the V3-2303 sequence polymorphism affected Hib PS binding. We constructed two Fab fragments that had the canonical Hib PS combining site VH-VL configuration but that had either V3-2301 or V3-2303. Radioantigen binding assay showed that on a concentration basis the V3-2303 Fab was 20-fold more effective in binding Hib PS than the V3-2301 Fab. The V3-2303 Fab was 4-fold more effective than the V3-2301 Fab in mediating facilitated bactericidal activity against Hib organisms. These findings identify a functional consequence of V3-23 allelism, and suggest that utilization of the V3-2303 gene in the human Hib PS repertoire would generate canonical antibodies with higher affinity and protective efficacy than canonical antibodies utilizing V3-23*01. Thus, IGH V gene allelic variation has the potential to impact the generation of protective immunity to Hib.