In vitro studies on human IgD. II. IgD-secreting cells preferentially elaborate IgD, lambda molecules.

Area of Science:

• Immunology
• Molecular Biology

Background:

• The IgD paradox highlights an unexpected discrepancy: IgD+ B cells typically express kappa light chains, yet secreted IgD proteins are predominantly lambda type.
• This phenomenon suggests a preferential association between delta heavy chains and lambda light chains in IgD-secreting cells.

Purpose of the Study:

• To investigate the preferential delta-lambda chain association in vitro.
• To analyze the relationship between cellular IgD location and delta-lambda chain association.
• To confirm the association in normal, nonmalignant human IgD-secreting B cells.

Main Methods:

• In vitro culture of tonsil supernatants to assess IgD secretion and lambda/kappa ratios.
• Fluorochrome-antibody double staining to analyze IgD-containing cells.
• Triton X-114 partitioning of cell lysates to differentiate membrane-enriched and intracellular fractions.
• Analysis of IgD lambda/kappa ratios in cell fractions and sera.

Main Results:

• Higher IgD-secreting cultures showed elevated IgD, lambda/kappa ratios, with stable IgD, kappa levels.
• IgD-containing cells in cultures predominantly displayed lambda chains, with some exclusively expressing lambda.
• Intracellular and supernatant fractions of IgD-secreting cells exhibited significantly higher IgD, lambda/kappa ratios compared to membrane-enriched fractions.
• Sera studies correlated total IgD with IgD, lambda/kappa ratios, supporting preferential lambda chain expression in secreted IgD.

Conclusions:

• The delta-lambda chain preferential association is a characteristic of normal, nonmalignant human IgD-secreting B cells, observed both in vitro and in vivo.
• This association is closely linked to the secretory form of IgD.
• The IgD, lambda/kappa ratio is a useful marker for monitoring IgD secretion.