Search

Autocrine production of growth factors is thought to be an essential element in the development of hemopoietic tumors in vivo. Tumor-derived cell lines frequently show this capability in vitro. It is not understood how autonomous growth in vitro is maintained by lymphoid cell lines that are not of tumorigenic origin. We have previously established human B cell clones that proliferate in serum-free media with unlimited potential. However, the cells need a critical density for continuous growth. Culture supernatant conditioned by these cell lines sustained proliferation even in low density cultures. All B cell clones analyzed were found to secrete the cytokines IL-1 alpha, IL-6, TNF-alpha, and TNF-beta whereas no activity of IL-2, IL-4, low m. w.-B cell growth factor, CSF, or IFN-gamma was recorded. In low density cultures supplemented with rIL-1 alpha, +/- IL-6, +/- TNF-alpha, and +/- TNF-beta together, B cell proliferation is maintained to the same extent as with conditioned medium. Addition of anti-sense oligonucleotides directed to the mRNA of IL-1 alpha, IL-6, and TNF-alpha, respectively, resulted in growth arrest and cell death. This effect could be prevented by supplementation with these cytokines. Scatchard plot analyses and internalization studies revealed that the cells express on their surface high affinity receptors for IL-1 alpha, IL-6, and TNF, respectively, and internalize the cytokines from the supernatant. These results demonstrate that (i) autonomous growth of immortalized B cells is maintained by secretion and reinternalization of IL-1 alpha, IL-6, TNF-alpha, and TNF-beta, (ii) these cytokines act in a synergistic fashion, and (iii) autocrine growth stimulation of human B cells in vitro does not necessarily represent their tumorigenic potential in vivo.

Human lymphocytes from peripheral blood were induced to proliferate indefinitely in vitro by transfection with cytoplasmic DNA isolated from transformed mouse L929 cells. Two cell lines analyzed proliferate in chemically defined, serum-free media without addition of cytokines. Using RIA and bioassays, the cells were found to secrete IL-1 alpha, IL-6, and TNF into the culture medium whereas no IL-2, IL-4, BCGF, CSF, or IFN-gamma were detected. Northern blot hybridizations revealed TNF alpha mRNA (1.5 kb) as well as TNF beta mRNA (1.4 kb) transcripts in RNA of the immortalized cells. Since the immortalized lymphoid cell lines neither form colonies in soft agar medium nor induce tumors after injection into immunodeficient nude mice, we suggest that these cytokines may be involved in autocrine growth stimulation of human lymphoid cell lines immortalized by transfection with cytoplasmic DNA from mouse L-cells.