Autoreactive marginal zone B cells are spontaneously activated but lymph node B cells require T cell help

Area of Science:

• Immunology
• Autoimmunity
• B cell biology

Background:

• Arthritis in K/BxN mice is caused by autoantibodies against glucose-6-phosphate-isomerase (GPI).
• Investigating B cell tolerance to ubiquitous autoantigens like GPI is crucial for understanding autoimmunity.

Purpose of the Study:

• To explore B cell tolerance mechanisms to the autoantigen glucose-6-phosphate-isomerase (GPI) in nonautoimmune mice.
• To determine how B cells with low affinity for GPI are regulated.

Main Methods:

• Utilized a low affinity anti-GPI heavy chain transgene to increase the frequency of GPI-reactive B cells in mice.
• Analyzed the distribution and functional state of these B cells in splenic marginal zone (MZ) and lymph node (LN) compartments.
• Assessed the capacity of B cells to secrete autoantibodies in response to T cell help in vitro and in vivo.

Main Results:

• Contrary to expectations, anti-GPI B cells were not tolerant to the autoantigen.
• Two distinct B cell populations emerged: activated cells in the MZ and antigenically ignorant cells in the LN pool.
• Increased autoantigen availability in the MZ drives B cell activation, while LN B cells remain functionally competent for T cell-dependent activation.

Conclusions:

• Low affinity autoreactive B cells exhibit distinct activation states based on autoantigen availability.
• Two activation pathways for autoreactive B cells exist: T cell-independent (MZ) and T cell-dependent (LN).
• These findings shed light on the complex regulation of B cell tolerance and autoimmunity.