Sea star factor blocks development of T-dependent antibody secreting clones by preventing lymphokine secretion

Area of Science:

• Immunology
• Marine Biology
• Biochemistry

Background:

• Sea star factor (SSF) is a 39 kDa protein from the echinoderm Asterias forbesi.
• SSF exhibits potent immunosuppressive effects on T-dependent antibody responses in vivo.
• Its specific mechanism of action on immune cells requires further elucidation.

Purpose of the Study:

• To investigate the immunosuppressive mechanism of Sea Star Factor (SSF) on T-dependent antibody production.
• To determine if SSF affects T cell-independent antibody responses.
• To explore the impact of SSF on cytokine production and availability.

Main Methods:

• In vitro clonal microculture assays using fluorescein (Flu)-specific B cells and conalbumin-specific T cells (D10.G4.1).
• Antigenic stimulation with Flu-conalbumin and T cell-independent stimulus (lipopolysaccharide - LPS).
• Analysis of immunoglobulin (Ig) secretion, cytokine concentrations in supernatants, and intracellular mRNA levels (IL-4, IL-5).

Main Results:

• SSF (0.5 microgram/ml) significantly inhibited T-dependent antibody production but not T cell-independent Ig secretion induced by LPS.
• Inhibition of antibody production was dose-dependently reversed by lymphokine-rich supernatants from stimulated T cells.
• SSF diminished detectable stimulatory cytokines in supernatants, suggesting reduced lymphokine availability, without altering intracellular IL-4/IL-5 mRNA levels.

Conclusions:

• Sea star factor (SSF) inhibits antibody responses by limiting the availability of helper T cell-derived lymphokines.
• The mechanism may involve direct effects on T cells or impaired T cell-B cell interactions.
• SSF's action highlights a novel pathway for immune modulation potentially relevant to understanding immune regulation.