Constitutive production of lymphokines by cloned murine B-cell lymphomas--CH12 B lymphoma produces interleukin-4.

B cells can be activated by T-independent antigens or mitogens such as lipopolysaccharide (LPS) which will induce proliferation and differentiation of the B cells into Ig-secreting cells, without the intervention of T cells. The precise mechanism of T-independent proliferation and differentiation of B cells is still unclear. It is possible however that antigen-stimulated B cells may produce some factors which play a role in T-independent B-cell responses. In addition, since it has now been established that B cells can function as antigen-presenting cells, it is possible that they too secrete a molecule which is involved in the activation of T cells, analogous to IL-1 production by antigen-presenting macrophages. A number of human B-cell lines, as well as human normal B cells activated appropriately, have been shown to produce various cytokines, and similar studies are now being undertaken in the mouse. In the present study, six cloned murine B-cell lymphomas of different origin were analyzed for the presence of mRNA encoding a number of lymphokines by hybridization of specific cDNA probes to poly-A RNA, followed by the sensitive S1 nuclease digestion technique. The lymphokines included (IL-) 1, 2, 3, 4, 5, and neuroleukin. Whereas none of the lines expressed detectable levels of IL-2, IL-3, or IL-5 mRNA, all the lines expressed high levels of neuroleukin mRNA. Three of the lymphomas (CH12, CH31, and NBL) expressed low levels of IL-1 mRNA. The most striking finding was that one lymphoma, CH12, constitutively expressed IL-4 mRNA. This mRNA appeared to be functional, as IL-4 activity measured by the HT-2 T cell proliferation assay could be detected in supernatants collected from CH12 cells. The growth-inducing activity of CH12 supernatant on HT-2 cells could be completely blocked by an anti-IL-4 monoclonal (11B11), but not by an anti-IL-2 antibody (S4B6), consistent with our observations that CH12 cells produce IL-4 but not IL-2. CH12 cells were also found to express high affinity receptors for IL-4. Proliferation of CH12 cells was not affected by the addition of exogenous IL-4. Addition of anti-IL-4 antibodies to CH12 cells in culture caused a slight but reproducible increase in their proliferation at low cell numbers, which is probably not highly significant. These findings open the possibilities that murine B lymphocytes are capable of lymphokine production or alternatively that aberrant lymphokine production underlies B-lymphocyte transformation.