Possamaï et al. studied the effects of IL-4 and IL-21 on CD40L-stimulated human blood B (CD40-B) cells. IL-21 induced CD40-B cell differentiation to antibody-secreting cells. IL-4 plus IL-21 induced CD40-B cells to expand and upregulate receptors that mediate homing to secondary lymphoid organs. IL-4 alone and IL-4 plus IL-21 induced CD40-B cells to secrete TH1- and TH2-associated cytokines and express molecules required for antigen presentation and T cell stimulation. In co-cultures, IL-4 plus IL-21 induced CD40-B cells to activate antigen-specific CD8+ T cells, and may provide an alternative to antigen-presenting DCs for vaccine/immunotherapy strategies.
Contributed by Paula Hochman
B lymphocytes have multiple functions central to humoral immunity, including Ag presentation to T cells, cytokine secretion, and differentiation into Ab-secreting plasma cells. In vitro expansion of human B cells by continuous IL-4 stimulation and engagement of their CD40 receptor by CD40L has allowed the use of these IL-4-CD40-B cells in research for the induction of Ag-specific T cell immune responses. However, in vivo, follicular helper T cells also influence B cell activity through the secretion of IL-21. The impact of both cytokines on multiple B cell functions is not clearly defined. To further understand these cytokines in CD40-B cell biology, we stimulated CD40-B cells with IL-4 or IL-21 or both (Combo) and characterized the proliferation, subsets, and functions of these cells. We demonstrate that IL-21- and Combo-CD40-B cells are highly proliferative cells that can be rapidly expanded to high numbers. We show that IL-21-CD40-B cells polarize to Ab-secreting plasma cells, whereas IL-4- and Combo-CD40-B cells are mostly activated mature B cells that express molecules associated with favorable APC functions. We further demonstrate that both IL-4- and Combo-CD40-B cells are efficient in promoting T cell activation and proliferation compared with IL-21-CD40-B cells. Thus, our study provides a better appreciation of CD40-B cell plasticity and biology. In addition, the stimulation of B cells with CD40L, IL-4, and IL-21 allows for the fast generation of high numbers of efficient APC, therefore providing a prospective tool for research and clinical applications such as cancer immunotherapy.