IL4 and B-cell chronic lymphocytic leukemia: In CLL, cell-surface IgM levels and BCR signaling is increased by the IL4 produced by T cells which also activates the JAK1-3/STAT6 pathway and upregulates the levels of anti-apoptotic proteins from BCL2 family, resulting in partial malignant B cell protection from the effects of “BCR inhibitors” (46, 47).