Identification of a human follicular dendritic cell molecule that stimulates germinal center B cell growth

Area of Science:

• Immunology
• Cell Biology

Background:

• Germinal center (GC) formation relies on initial interactions between B cells and follicular dendritic cells (FDCs).
• Identifying molecules that regulate B cell-FDC interactions is crucial for understanding GC development.

Purpose of the Study:

• To identify and characterize molecules involved in B cell-FDC interactions that regulate B cell growth and differentiation.
• To investigate the role of the novel 8D6 antigen in mediating FDC-dependent B cell costimulation.

Main Methods:

• Generation and screening of FDC-staining monoclonal antibodies (mAbs) for inhibitory activity.
• Expression cloning of the cDNA encoding the 8D6 antigen from a human FDC line.
• Functional assays using COS cell transfectants and B cell cultures to assess B cell growth and proliferation.
• Inhibition studies using the 8D6 mAb on CD40 ligand-stimulated GC B cells and a GC lymphoma cell line.

Main Results:

• A novel protein, the 8D6 antigen (Ag), was identified and found to be abundantly expressed on FDCs.
• The 8D6 Ag, when expressed on COS cells, stimulated B cell growth.
• The 8D6 mAb completely blocked the costimulatory function of the 8D6 Ag.
• The 8D6 mAb inhibited cell cycle progression of CD40 ligand-stimulated GC B cells and the growth of a GC lymphoma line dependent on FDCs.

Conclusions:

• Follicular dendritic cells primarily function to stimulate B cell growth within the germinal center.
• The 8D6 antigen is a key FDC-derived signaling molecule mediating B cell growth stimulation.
• Targeting the 8D6 Ag may offer a strategy to modulate GC B cell responses.