IL 2 restores memory B cell activation by antigen-specific T cell clone variants

Area of Science:

• Immunology
• Cellular immunology
• T cell and B cell interactions

Background:

• Two pathways exist for T cell clones to induce B cell differentiation.
• High-dose antigen drives primary anti-TNP responses, while low-dose antigen elicits IgG responses in primed B cells.
• Variant T cell clones exist that lack low-dose antigen helper activity but retain high-dose activity.

Purpose of the Study:

• To investigate the role of interleukin 2 (IL 2) in low-dose, antigen-driven T cell responses.
• To determine the requirement for accessory cells in IL 2-mediated low-dose responses.
• To explore the mechanism of accessory cell involvement in T cell-dependent B cell differentiation.

Main Methods:

• Utilized a variant T cell clone lacking low-dose helper activity.
• Assessed IL 2's ability to reconstitute low-dose antigen responses.
• Investigated accessory cell requirements by removing adherent cells and performing add-back experiments.
• Tested the ability of concanavalin A (Con A) supernatant and IL 1 to replace accessory cell function.

Main Results:

• IL 2 reconstituted the low-dose, antigen-driven helper activity in the variant T cell clone.
• Removal of adherent cells abolished the IL 2-induced low-dose response.
• The accessory cell population did not require MHC restriction for reconstituting the IL 2-dependent response.
• Con A supernatant, but not IL 1, could replace the function of adherent cells.

Conclusions:

• IL 2 bypasses MHC-restricted interactions between T cells and antigen-presenting cells in this system.
• B cells efficiently present antigen for primary responses, but require additional factors for IgG production.
• Adherent cells are crucial for IgG production in primed B cells, likely via soluble factors present in Con A supernatant.