Molecular investigation of the cytokines produced by normal and malignant B lymphocytes

Different normal and malignant human B-cell populations were studied with a twofold aim: to define which cytokines are produced in vivo, and to assess the relationship between cytokine production and kinetic state. To analyse normal B-cells representative of different stages of activation and proliferation in vivo, we purified germinal centre (GC)-B blasts and mantle B (M-B) cells from tonsils. To compare malignant B lymphocytes with their closest normal equivalent cells, we separated malignant CD5⁺B lymphocytes from the peripheral blood of patients with B-chronic lymphocytic leukemia (B-CLL) and normal CD5⁺B lymphocytes from cord blood. The expression of interleukins (IL) IL-1α, IL-1β, tumour necrosis factor α (TNF-α), transforming growth factor β (TGF-β), IL-2, IL-4, and IL-6 genes was analysed using Northern and Western blotting techniques. TNF-α mRNA is produced by resting (M-B) and actively proliferating (GC-B) normal B lymphocytes. TGF-β mRNA is present at high levels in resting normal M-B cells, while the transcript levels are lower in proliferating GC-B and in activated CD5⁺B lymphocytes. IL-2 production is limited to the actively proliferating GC-B blasts, IL-1β and IL-6 to resting M-B cells. The cytokine production profile of CD5⁺ malignant B-CLL cells differs from that of their putative normal counterparts and is more like the profile of M-B cells, since B-CLL cells produce IL-1β, TNF-α, TGF-β, and IL-6. These observations lead to the following conclusions: among normal B lymphocyte populations, resting M-B lymphocytes are the most active cytokine producers, and B-CLL malignant B cells reflect the production pattern of normal resting B lymphocytes.