Allotyping human complement factor B in Asian Indian type 1 diabetic patients

Area of Science:

• Immunogenetics
• Molecular Biology
• Human Genetics

Background:

• Human complement factor B (BF) is vital for the alternate complement pathway, playing a key role in innate immunity and autoimmune responses.
• The BF gene resides within the major histocompatibility complex (MHC) and encodes numerous protein variants, with three primary alleles (BF*S, BF*FB, BF*FA) differing at codon 7.

Purpose of the Study:

• To develop and validate a novel polymerase chain reaction (PCR) assay using sequence-specific primers (SSP) for precise allotyping of BF alleles.
• To investigate the distribution of BF alleles within human leukocyte antigen (HLA)-DR3 haplotypes in the Indian population, particularly in relation to autoimmune diseases.

Main Methods:

• Development of a novel sequence-specific primer (SSP)-based PCR assay for identifying nucleotide substitutions at codon 7 of the BF gene.
• Validation of the SSP assay through sequencing and amplified fragment length polymorphism (AFLP) analysis.
• Application of the SSP assay to determine BF allele frequencies in North Indian type 1 diabetes (T1D) patients and healthy controls, focusing on specific MHC haplotypes.

Main Results:

• The novel SSP assay accurately identified nucleotide variations in all three BF alleles (BF*S, BF*FB, BF*FA).
• In North Indian T1D patients, the HLA-A26-B8-DR3 (ancestral haplotype AH8.2) was the most common MHC haplotype, carrying the BF*FB allele.
• The BF*FB allele was significantly overrepresented in North Indian T1D patients (51.03%) compared to healthy controls (32.7%), indicating a strong association with T1D in this population (OR = 2.148, P = 0.002).

Conclusions:

• The developed SSP assay is a reliable tool for BF allotyping, crucial for understanding immune responses and disease associations.
• The BF*FB allele, associated with the AH8.2 haplotype, shows a significant overrepresentation in North Indian T1D patients, highlighting its role in autoimmunity.
• Further population-based studies on BF allotyping within diverse MHC haplotypes are essential for elucidating MHC diversification mechanisms and guiding therapeutic strategies for autoimmune diseases.