Autoimmune-prone mice bear a hyper-active B cell population generated spontaneously in peripheral lymphoid organs. Expression of β RNA-primase GANP was shown to be an activation marker in lymphoid follicle germinal center (GC) B cells after immunization with T cell-dependent antigen (TD-Ag) in normal mice. In this study, we examined the expression of GANP in lymphoid tissues of autoimmune-prone mice. GANP expression was up-regulated in GC-B cells after stimulation with TD-Ags; however, highly GANP-positive (GANPhi) cells were also observed in lymph nodes of non-immunized MRL/lpr mice. GANPhicells in lymph nodes as well as in spleens of the different autoimmune-prone strains, MRL/lpr, NZB, (NZB×NZW)F1 and BXSB, gradually increased with age. This population was detected only in small numbers in the red pulp region of the spleen after immunization with TD-Ag in normal C57BL/6 and BALB/c mice. GANPhicells had a B220-IgM+Syndecan-1+phenotype, but were negative for PAS-staining and bromo-deoxyuridine incorporation. These results demonstrate that GANPhiplasma-like cells appear in lymph nodes of autoimmune mice during aging, suggesting that the new plasma cell population might be generated after hyper-activation of B cells during the course of autoimmune disease.
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