The human VH3b gene subfamily is highly polymorphic

Area of Science:

• Immunology
• Genetics
• Microbiology

Background:

• Human antibodies targeting Haemophilus influenzae type b (Hib) are primarily encoded by VH3 gene family members, particularly the VH3b subfamily.
• Previous research indicated a limited set of VH3 genes contribute to anti-Hib polysaccharide antibody production.

Purpose of the Study:

• To directly investigate the human VH3 germline repertoire available for anti-Hib polysaccharide antibody generation.
• To analyze the genetic diversity and conservation of VH3b germline genes in unrelated individuals.

Main Methods:

• Polymerase chain reaction (PCR) was employed to amplify and clone candidate germline VH3b heavy chain V region genes.
• Germline genes were isolated from two unrelated subjects who had previously produced anti-Hib polysaccharide monoclonal antibodies (mAbs).
• Sequencing and homology analysis were performed on the amplified germline VH3b genes.

Main Results:

• One subject yielded a single functional VH3b germline gene, identical to the known gene 9.1.
• The second subject provided twelve distinct VH3b germline sequences with high homology (87.6-99.8%) to each other.
• These germline VH3b genes exhibited significant homology (82.7-94.1%) to previously identified rearranged anti-Hib polysaccharide VH3b segments from the same subjects.
• Identified genes LSG1.1 and LSG6.1 were identical to the 9.1 germline gene and the M85 cDNA, respectively.

Conclusions:

• The human VH3 repertoire is subject to considerable polymorphism within the population.
• Despite extensive germline VH segment diversity, certain genes demonstrate high conservation in the outbred human population.
• This suggests a selective pressure maintaining specific VH3b genes for effective immune responses against pathogens like Hib.