'Autoreactivity' of some hybridomas may be caused by a three-cell interaction

We have produced hybridomas by the fusion of BALB/c (H-2d) bone marrow cells, bone marrow cells from BALB/c-nu/nu mice, BALB/c fetal liver cells, and BALB/c fetal thymocytes with the AKR (H-2k) thymoma BW5147. The hybridomas were selected for the expression of the Thy-1.2 antigen of the normal cell donor and for their ability to produce IL-2 upon co-culture with irradiated normal spleen cells. The hybridomas produce IL-2 when co-cultured with H-2k, H-2u, H-2j, or H-2v cells of some strains but not in mixtures with H-2p, H-2s, H-2f, H-2b, H-2q, or H-2d cells. An investigation into the nature of these differences revealed a novel type of interaction between hybridomas, mature T lymphocytes and class II-positive spleen or lymph node cells. The experiments described in this communication suggest that irradiated L3T4+, Ly-1 High T cells recognize syngeneic class II-positive spleen or lymph node cells, but only in some strains. The ability to recognize the syngeneic cells depends both upon the H-2 complex and on the non-H-2 genes. The recognition leads, in the absence of proliferation, to the secretion of an as yet unidentified and largely hypothetical factor which then acts on the hybridoma cells. Upon stimulation with the T lymphocyte-derived factor, the hybridoma cells begin to secrete IL-2, which can then be measured by the proliferation of the IL-2-dependent CTLL line. The IL-2 production by the hybridoma cells is independent of their proliferation. The described interaction apparently does not involve the T-cell receptor of the hybridoma cells. The interaction resembles the autoreactivity of thymocyte hybridomas described by other investigators, and therefore it is possible that this 'autoreactivity' may in fact be generated by a similar mechanism to the one described here.