A Screening Platform for Immunomodulatory Compounds Targeting B Lymphocytes

B cells play a critical role in humoral immunity as part of the adaptive immune system with roles in antigen presentation, cytokine secretion and antibody production. B cells can be activated via different pathways, including T cell-independent (TI) and T cell-dependent (TD) mechanisms.

Furthermore, B cell activity can be modulated by a B-cell-activating factor (BAFF), a survival and maturation factor for B cells. Abnormal B cell activity can lead to many B cell-specific malignancies and autoimmune diseases, including systemic lupus erythematosus and B-cell lymphomas. Here, we establish an in vitro screening platform to study B cell activity and assess compounds specifically targeting B cell signalling and function. 

Following stimulation with either CpG-ODN + IL-15 (a model for TI activation) or CD40L + IL-4, (a model for TD activation) there was a marked increase in B cell activation marker expression (CD71, CD80, CD86) and proliferation (analysed by Flow Cytometry) compared to unstimulated B cells. Moreover, BAFF augmented this response with similar activity after 6 or 9 days of culture. As measured by Flow Cytometry, the frequency of B cell subpopulations (IgD+ memory, IgD- memory cells and plasmablasts) increased with TI and TD stimulation. Moreover, the proportion of these subpopulations was further enhanced with BAFF treatment. B cell-specific inhibitors ((BTK (ibrutinib) and Syk (BAY-61-3606)) and the immunosuppressant dexamethasone reduced B cell activation, proliferation and IgG secretion elicited by CpG-ODN. 

We have validated an in vitro model of B cell activity (proliferation, activation, IgG production) using both TD and TI stimuli and further confirmed this model using specific B cell inhibitors and a general immunosuppressant. This allows for the screening of therapeutics targeting B cell signalling and function for treating autoimmune conditions.