The production of interleukin 1 by a differentiating rat myelomonocytic leukemia line

We have succeeded in isolating a rat myelomonocytic leukemia cell line (c-WRT-7) that is capable of producing a factor with biological and biochemical properties similar to those ascribed to interleukin 1 (IL-1). Lipopolysaccharides (LPS), phorbol myristate acetate (PMA) and mezerein were found to be capable of inducing c-WRT-7 cells to secret IL-1, while non-stimulated c-WRT-7 cells were unable to produce any IL-1 whatever. After treatment of c-WRT-7 cells with LPS, IL-1 activity reached a maximum level after approximately 48 hrs of culture. Supernatants from LPS-stimulated c-WRT-7 cells promoted the proliferation of thymocytes initiated by suboptimal doses of lectins, and restored depressed mitogenic responses of macrophage depleted spleen cells. However, no detectable interleukin 2 (IL-2) activity was observed in the supernatants of LPS-stimulated c-WRT-7 cells. The IL-1 from c-WRT-7 cells had an apparent molecular weight between 15,000 and 20,000 when measured by gel filtration. The thymocyte comitogenic activity was maintained mainly at alkaline pH and the reduction was noted at the pH below 4. The activity was partially inactivated by heating at 60 degrees C for 60 min or at 70 degrees C for more than 10 min. Papain and pronase reduced the activity completely, whereas chymotrypsin and trypsin had little effect. To our knowledge this is the first established rat myelomonocytic leukemia cell line that has been found to be capable of producing IL-1.