Epstein-Barr Virus-containing B-cell Line Produces an Interleukin 1 That It Uses As a Growth Factor

We report the establishment of a spontaneous interleukin 1 (IL-1)-producing subclone derived from the human Epstein-Barr virus (EBV)-containing B-lymphoblastoid cell line (721 LCL) and show that the IL-1 produced by this B-cell subclone is distinct from other types of IL-1. The parental cell line 84.5, a deletion mutant of the 721 LCL cell line, can be induced to produce IL-1 activity when stimulated by certain inducers such as phorbol 12-myristate 13-acetate in the presence of fetal calf serum. From this parental 721/84.5 clone, a subclone, termed 3B6, has been developed. This 3B6 subclone has an immature B-cell phenotype, expresses only HLA class II DP subregion antigens, and spontaneously releases IL-1 in the culture supernatant with relatively few inhibitory molecules under serum-free culture conditions. The 3B6-derived IL-1 was purified from 3B6 conditioned medium with a three-step procedure. The molecular weight of this IL-1 is 13,500, and the isoelectric point values are pH 4.9 and 5.1 without any component focusing near pH 7. The N-terminal amino acid sequence differs markedly from those reported for the two IL-1 species produced by monocytes. The purified material shares several biological properties with monocyte IL-1, since it could induce the proliferation of murine thymocytes, the production of interleukin 2 by phytohemagglutinin-stimulated cloned HSB2 T cells, and the proliferation of human fibroblasts. However, this IL-1 activity could not be blocked by polyclonal anti-monocytic IL-1 antibodies, and, more importantly, it was not pyrogenic in rabbits. Finally, it promotes the growth of B-cell clones derived from the parental 721/84.5 lines in the absence of fetal calf serum, which suggests that it could act as an autocrine growth factor in this Epstein-Barr virus-transformed B-cell line.