B cells regulate thymic CD8⁺T cell differentiation in lupus-prone mice.

Area of Science:

• Immunology
• Autoimmune Diseases
• T cell Biology

Background:

• Thymic B cells are crucial for T cell negative selection under normal conditions.
• The role of thymic B cells in T cell differentiation during autoimmune diseases like systemic lupus erythematosus (SLE) requires further investigation.

Purpose of the Study:

• To investigate the effect of thymic B cells on T cell differentiation in lupus-prone mice.
• To elucidate the mechanisms by which B cells influence T cell populations in SLE.

Main Methods:

• Comparative analysis of thymic T cell populations (CD4+, CD8+, CD4+CD8+) in lupus-prone mice versus controls.
• Assessment of T cell differentiation following B cell reduction.
• Identification and characterization of novel thymic T cell populations using flow cytometry and gene expression analysis (RORγt).
• Investigation of the role of IgG in T cell differentiation.

Main Results:

• Lupus-prone mice exhibited increased thymic B cells, CD8- CD4+ and CD4- CD8+ T cells, and decreased CD4+CD8+ T cells.
• B cell reduction reversed these changes.
• B cells inhibited the differentiation of thymic immature single positive (ISP) CD4-CD8+CD3lo/-RORγt- T cells into CD4+CD8+ T cells.
• A novel population of thymic immature CD4-CD8+CD3loRORγt+ T cells was identified, induced into mature CD4-CD8+CD3+RORγt+ T cells by B cells.
• Thymic B cell-derived IgG was critical for the differentiation of thymic CD8+ISP and mature RORγt+CD8+ T cells.

Conclusions:

• In lupus-prone mice, thymic B cells impede CD8+ISP T cell differentiation while promoting a novel RORγt+CD8+ T cell subset.
• B cell-secreted IgG is a key mediator in driving the differentiation of these specific T cell populations in the context of SLE.