J chain biosynthesis in pre-B cells and other possible precursor B cells

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• J chain is a protein component of polymeric immunoglobulins.
• Its synthesis and role in early B cell differentiation are not fully understood.

Purpose of the Study:

• To investigate the onset of J chain biosynthesis during B cell ontogeny.
• To determine if J chain synthesis precedes immunoglobulin secretion.

Main Methods:

• In vivo pulse labeling of human B cell lines.
• In vitro translation using a wheat germ cell-free system.
• Analysis of J chain products via serologic criteria, SDS-PAGE, gel electrophoresis, and peptide mapping.

Main Results:

• J chain synthesis was detected in various B cell precursors, including pre-B-like and surface IgM-expressing lines.
• The primary translation products of J chain were identical across all tested cell lines.
• J chain biosynthesis was observed before the development of immunoglobulin-secreting cells.

Conclusions:

• J chain biosynthesis is an early event in B cell differentiation.
• The findings suggest a fundamental role for J chain in the biosynthesis of all immunoglobulins at different differentiation stages.