Analysis of soluble and cell surface factors regulating anti-DNA topoisomerase I autoantibody production demonstrates synergy between Th1 and Th2 autoreactive T cells

The cellular and subcellular events governing Ab production with specificit y for self Ags are poorly understood. In this study we examined the role of cellular interactions and cytokines in regulating the production of anti-D NA topoisomerase I (topo I) Ab, a major autoantibody in patients with syste mic sclerosis (SSc), Topo I-specific T cell clones derived from SSc subject s and healthy donors were cultured with autologous peripheral blood B cells . Anti-topo I Ab production was induced by five of seven topo I-specific T cell clones derived from SSc subjects, but by none of eight T cell clones g enerated from healthy controls. However, two of the T cell clones from heal thy controls provided help to HLA-DR-matched SSc B cells to produce anti-to po I Ab, The analysis of cytokine mRNA expression revealed that the ability to promote anti-topo I autoantibody production was strictly correlated wit h IL-2 and IL-6 expression by the T cell clones. Kinetic studies showed tha t IL-2 was required throughout the culture period for maximal autoantibody production and that both MHC-TCR and CD40-CD40L interactions were essential during the early phase of the culture. IL-6 was important in the late phas e. Th1 clones (producing IL-2, but no IL-6) and Th2 clones (producing IL-6, but no IL-2) synergically activated autologous B cells to produce anti-top o I Ab, These results indicate that T cell-dependent B cell activation resu lting in anti-topo I autoantibody production requires a series of temporall y defined cell contact and soluble stimuli.