Interleukin-2 effects on human B cells activated in vivo

Area of Science:

• Immunology
• Cell Biology

Background:

• The precise physiological role of interleukin-2 (IL-2) in B-cell immune responses remains incompletely understood, despite the expression of functional IL-2 receptors (IL-2R) on activated B cells.
• Activated T cells are known to proliferate vigorously in response to IL-2, utilizing IL-2R (Tac antigen) for growth perpetuation.

Purpose of the Study:

• To investigate the role of recombinant IL-2 (rIL-2) in the proliferation, IL-2R expression, and terminal differentiation of human tonsillar B cells.
• To compare the effects of IL-2 on B cells with its known effects on T cells from the same source.

Main Methods:

• Separation of human tonsillar lymphocytes into B and T cell subpopulations.
• Enrichment of resting and preactivated cells based on cell density and activation antigen expression (Tac, Bac-1).
• Culture of B and T cells with rIL-2 and analysis of IL-2R expression, proliferation, and immunoglobulin secretion.

Main Results:

• Activated T cells showed robust proliferation and heightened IL-2R (Tac) expression upon IL-2 stimulation.
• Relatively few resting B cells expressed IL-2R, but rIL-2 increased Tac+ B cells with a minimal proliferative response.
• rIL-2 induced a transient proliferative response in a subpopulation of activated B cells (Bac-1+) expressing IL-2R, enhancing immunoglobulin secretion.
• IL-2-induced Tac+ B cells were larger and a fraction produced and secreted immunoglobulins, with this enhancement blocked by anti-Tac antibody.

Conclusions:

• IL-2 transiently upregulates IL-2R (Tac) expression on activated B cells.
• IL-2, through IL-2R, facilitates the terminal growth and differentiation of activated B cells into immunoglobulin-secreting plasma cells.
• These findings clarify a significant aspect of IL-2's role in adaptive immunity, specifically within B cell maturation pathways.