Together with 2 × 105 allogenic T cells, 5 × 104-irradiated CD19+ CD25+ or CD19+ CD25− B cells were incubated in Iscoves medium at a final volume of 200 μl in triplicates. As control 2 × 105 T cells in medium without any stimuli or stimulated BTK inhibitor libraries with 5 μg/ml ConA (Sigma-Aldrich) were used. Cells were incubated in a humidified atmosphere containing 5% CO2 at 37° for 48 h and pulsed with 1 μCi 3H-thymidine for additional 8 h, harvested and analysed as described previously. ELISPOT assay for evaluation of Ig production.  Ninety-six well plates (Millipore Corporation, Billerca, MA, USA) were coated with affinity-purified goat F(ab’)2 fragments specific for mouse Ig(H + L) (MP Biomedicals, Aurora, OH, usa) at 0.25 μg

per well overnight at 4 °C. After washing with PBS, plates were blocked with 5% FCS in PBS for one hour at room temperature. Splenic B cells, sorted into CD19+ CD25+ and CD19+ CD25−, were

added in a serial dilution of 1000, 10,000, 50,000 and 70,000 cells per well in duplicates in 50 μl complete Iscove’s medium followed by incubation in a humidified atmosphere containing 5% CO2 at 37° for 4 h. After washing the plates, alkaline phosphatase-labelled goat anti-mouse IgA, IgG or IgM (Southern Biotechnology, Birmingham, AL, USA) were added at optimal concentration and plates were incubated overnight at 4 °C. After another washing step, BCIP/NBT (Bio-Rad Laboratories, Hercules, CA, USA) was added for 20–30 min at room temperature. Spots were counted using a microscope and the results are presented as spot-forming cells (SFC) per 70,000 B cells. drug discovery OVA-specific ELISPOT.  Ninety-six well plates (Millipore Corporation) were coated with 25 μg/ml of OVA dissolved in PBS overnight at 4 °C. After washing with PBS, uncoated sites were blocked with 5% FCS in PBS for one hour at room temperature. Splenic B cells from OVA-immunized mice,

sorted into CD19+ CD25+ and CD19+ CD25−, were plated in duplicates of 50,000, 25,000 and 10,000 cells per well in 50 μl complete Iscove’s medium. The assay was performed as described in the paragraph above and presented as spot-forming cells (SFC) per 106 B cells. Immunization with pheromone OVA.  Ovalbumin (Sigma-Aldrich) was dissolved in PBS and filtered using through a 40-μm filter (Millipore Corporation Bedford, MA, USA). NMRI mice (n = 10) were immunized by an intraperitoneal injection with 100 μg of OVA mixed with Freund’s complete adjuvant (Sigma-Aldrich). Seven days later, the mice were boosted, as previously described [12]. The animals were sacrificed on day 14 after immunization, and CD19+ CD25+ and CD19+ CD25− B cells were sorted from the spleens as previously described. OVA-specific ELISPOT assay was performed on the sorted cells. Migration assay.  The ability of CD19+ CD25+ or CD19+ CD25− B cells to migrate towards recombinant mouse, CXCL13 (R&D) was analysed using the ChemoTx system with pore size of 3 μm (Neuro Probe Inc.