Naive CD4 T cells constitutively express CD40L and augment autoreactive B cell survival

Area of Science:

• Immunology
• Autoimmunity
• Cellular Biology

Background:

• Chronic B cell receptor engagement by soluble autoantigen typically reduces B cell survival.
• The role of T cell-mediated signaling in regulating autoreactive B cell survival under homeostatic conditions is not fully understood.

Purpose of the Study:

• To investigate the impact of CD4 T cells and CD40 signaling on the survival of autoreactive B cells.
• To elucidate the mechanism by which the CD40L-CD40 pathway influences B cell homeostasis in the absence of T cell activation.

Main Methods:

• Utilized the Ig and hen egg lysozyme double transgenic mouse model.
• Employed mixed bone marrow chimera experiments.
• Analyzed CD40L and CD40 expression on naive CD4 T cells and other immune cells.

Main Results:

• Survival of autoantigen-engaged B cells was further reduced in mice lacking CD4 T cells or deficient in CD40.
• The CD40L-CD40 pathway augmented autoreactive B cell survival in a non-cell-autonomous manner under homeostatic conditions.
• Naive CD4 T cells constitutively express CD40L, though cell surface abundance is low.

Conclusions:

• The CD40L-CD40 pathway can enhance the survival of autoantigen-engaged B cells independently of T cell activation.
• Constitutive CD40L expression by naive CD4 T cells may shape the B cell repertoire and impact regulatory T cell homeostasis.