Immunoglobulin kappa light chain germ-line transcripts in human precursor B lymphocytes

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Severe combined immunodeficiency (SCID) patients exhibit a lack of immunoglobulin gene rearrangements.
• B lymphoblastoid cell lines (BLCL) from SCID patients were analyzed for immunoglobulin (Ig) heavy (H) and light (L) chain loci.
• The study investigated germline transcripts in the Ig kappa region.

Purpose of the Study:

• To characterize germline transcripts of the Ig kappa locus.
• To identify novel gene segments and regulatory elements involved in Ig gene expression.
• To determine the presence of these transcripts in both SCID and normal developing lymphocytes.

Main Methods:

• cDNA cloning and sequence analysis of Ig kappa transcripts.
• Genomic restriction mapping and DNA sequencing.
• Analysis of BLCL from SCID patients and normal fetal bone marrow.

Main Results:

• Absence of genomic rearrangements in Ig H and L chain loci in SCID BLCL.
• Identification of a 1.2 kb germline transcript containing a novel 5' segment (human kappa zero).
• Human kappa zero segment located upstream of J kappa 1, containing a putative promoter with an OCT2 binding site.
• Expression of kappa zero gene segment found in normal developing pre-B lymphocytes.

Conclusions:

• Germline Ig kappa L chain transcripts are present in both SCID and normal developing B lymphocytes.
• The human kappa zero segment and its regulatory elements are involved in Ig kappa locus regulation.
• Expression of these transcripts may indicate locus accessibility for gene rearrangement.