IL6 and B-cell chronic lymphocytic leukemia: These levels were linearly correlated [19], possibly indicative of a positive feedback loop between the two cytokines with IL-17A directly influencing IL-6 production in CLL patients, and IL-6, an important cytokine in the differentiation of Th17 cells, in turn regulating levels of Th17, the major source of IL-17A [35].