FOS and diffuse large B-cell lymphoma: Therefore, we propose a hypothetical model for growth regulation by IL-21 in EBV-positive DLBCL in which IL-21 signalling leads to STAT3 phosphorylation and induces LMP-1 expression to form a positive autoregulatory loop, which amplifies the signals for Myc and AP-1 (composed of homoor heterodimers formed by related Jun and Fos family proteins) transcription (Fig. 7a).