Variable region sequences of a protective human monoclonal antibody specific for the Haemophilus influenzae type b capsular polysaccharide

Abstract

A hybridoma secreting a human immunoglobulin G2 κ monoclonal antibody (MAb) specific for the capsular polysaccharide of Haemophilus influenzae type b (Hib) was isolated. This MAb, designated CA4, was bactericidal to Hib in vitro and protected infant rats from Hib bacteremia. Nucleotide sequence analysis of CA4 variable (V) region cDNA showed that the heavy (H)-chain V region was of subgroup III and was 96% identical to the V(H) germ line gene segment DP77 (V3-21). The light (L)-chain V region was of the κ subgroup III and was 94% identical to the A27 (Humkv325) germ line gene, which is commonly used by rheumatoid factors and other autoantibodies. MAb CA4 did not have rheumatoid factor activity and did not react with histones, DNA, or chromatin. These findings identify an additional V(H)III gene segment which can contribute to the anti-Hib capsular polysaccharide repertoire and demonstrate that a V(L) gene commonly encoding autoantibodies can be utilized for protective immunity.