The Small Rho GTPases Rac1 and Rac2 Are Important for T-Cell Independent Antigen Responses and for Suppressing...

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Rho GTPases, including Cdc42, Rac1, and Rac2, are key regulators of cellular processes like adhesion, migration, and proliferation.
• Previous studies indicated that combined deletion of Rac1 and Rac2 in early B cell development prevents splenic white pulp entry.

Purpose of the Study:

• To investigate the specific roles of Rac1 and Rac2 in B cell functionality and the humoral immune response.
• To overcome migratory defects by using an inducible deletion system.

Main Methods:

• Generated Rac1-inducible Rac2-deficient (Rac1^BRac2^-/-) mice to study B cell function in the spleen.
• Assessed B cell populations, adhesion, proliferation, and antibody responses to T-cell-independent and T-cell-dependent antigens.
• Analyzed in vitro immunoglobulin (Ig) class switching.

Main Results:

• Rac1^BRac2^-/- mice exhibited normal splenic B cell differentiation but reduced marginal zone B cells.
• Rac1^BRac2^-/- B cells showed normal spreading but reduced homotypic adhesion and proliferation.
• Antibody responses to T-cell-independent antigens were reduced, while IgG1 and IgG2b titers increased against T-cell-dependent antigens.
• In vitro studies revealed elevated germline γ2b transcripts and increased IgG2b class switching in Rac1^BRac2^-/- B cells.

Conclusions:

• Rac1 and Rac2 play significant roles in regulating B cell humoral immune responses.
• These GTPases appear to suppress immunoglobulin class switching to IgG2b.