Interleukin-2 enhances the production of tumor necrosis factor-alpha in activated B-type chronic lymphocytic leukemia (B-CLL) cells.
Tumor necrosis factor-alpha (TNF-alpha) has recently been implicated as a regulator growth and differentiation of normal and malignant B cells. We utilized a selected clone (I-83) of primary resting B-type chronic lymphocytic leukemia (B-CLL) cells, inducible to activation, growth and differentiation in vitro, as a model system to study the possible role of TNF-alpha as an autocrine growth factor for such cells. Our results show that unstimulated I-83 B-CLL cells produced a low level of TNF-alpha mRNA, as shown by Northern blot analysis, and cytoplasmic TNF-alpha, determined in individual cells by immunocytochemistry. Secreted TNF-alpha could, however, not be detected in the medium by ELISA. TNF-alpha synthesis and secretion was, however, induced to high levels by stimulation of the B-CLL cells with interleukin-2 (IL-2) after activation by 12-O-tetradecanoylphorbol-13-acetate (TPA) or Staphylococcus aureus Cowan strain I (SAC) and B-cell stimulatory factor-MP6 (thioredoxin). A moderate increase in TNF-alpha secretion was also induced by TPA or IL-2 alone. IL-4 did not have any major effects on the production of TNF-alpha in activated cells, but inhibited the IL-2-induced production of TNF-alpha in SAC-activated cells. The cell surface expression of TNF-alpha receptors (TNF-R), as determined by binding assay using 125I-labelled recombinant TNF-alpha (rTNF-alpha), was also induced after SAC or TPA activation, but shed receptors (TNF-binding proteins) were only observed after TPA activation. Exogenously added rTNF-alpha in combination with TPA or SAC induced a high level of DNA synthesis in I-83 B-CLL cells. The increased endogenous production and secretion of TNF-alpha during induced growth stimulation, the induced expression of TNF-R, and the mitogenic effect of TNF-alpha on activated B-CLL cells raise the question whether TNF-alpha may function as an autocrine co-stimulator of B-CLL cell growth as recently suggested. anti-TNF-alpha and anti-TNF-R antibodies, however, failed to inhibit the IL-2- and IL-4-induced proliferation of activated I-83 B-CLL cells.
Department of Pathology, University of Uppsala, University Hospital, Sweden.
L G
LG
Larsson
M
M
Carlsson
M
M
Schena
M
M
Lantz
F
F
Caligaris-Cappio
K
K
Nilsson
D004273:DNA, Neoplasm / Q000096:biosynthesis; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology*; D015847:Interleukin-4 / Q000494:pharmacology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018124:Receptors, Tumor Necrosis Factor; D013211:Staphylococcus aureus; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013879:Thioredoxins / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis* / Q000235:genetics
D004273:DNA, Neoplasm; D007376:Interleukin-2; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D015847:Interleukin-4; D013879:Thioredoxins; D013755:Tetradecanoylphorbol Acetate