Nucleobindin (Nuc) was originally identified as a 55 kDa protein that enhanced anti-DNA antibody production when added to cultures of autoimmune MRL/lpr mouse spleen cells. Nuc is a DNA- and calcium-binding leucine zipper protein whose physiological functions remain unknown. In previous studies, the authors showed that Nuc is not only able to augment anti-DNA production in vitro, but also to accelerate the autoimmune response in vivo in MRL/+/+ mice. Moreover, Nuc mRNA expression was found to be increased in lymphatic organs of lupus mice. To verify if Nuc is involved in anti-DNA production by stimulating autoreactive T cells, the authors studied the T-cell response both in lupus mice and in normal mice injected with recombinant Nuc (rNuc).