INTERLEUKIN-6 IS REQUIRED FOR PRISTANE-INDUCED PLASMA-CELL HYPERPLASIA IN MICE

Intraperitoneal injection of pristane induces production of interleuki n-6 (IL-6) and either plasmacytosis or plasmacytoma in mice, depending upon the genetic background Pristane does not induce plasmacytoma in IL-6 knockout (IL-6-/-) mice, suggesting that IL-6 is required for thi s process. In the present study we determined whether IL-6 is also req uired for pristane-induced hyperplasia of normal plasma cells. Pristan e was injected intraperitoneally into IL-6-/- and IL-6 wild-type (IL-6 +/+) mice. Overall there were more deaths in IL-6+/+ mice (85%) than i n IL-6-/- mice (40%), P = 0.024, Hyperplastic lymph node and spleen we ight did not differ (P = 0.82 and P = 0.15, respectively) in IL-6-/- v ersus IL-6+/+ mice. Lymphocytosis with similar patterns of expression of B-cell (B220) and T-cell (Thy-1) antigens was noted in both IL-6-/- and IL-6+/+ mice. However, morphological studies, dual fluorescent st aining for Syn-1 and B220 antigens (syn-1(+) B220(+) cells), and intra cytoplasmic Ig staining revealed plasma cell hyperplasia in lymph node and spleen from IL-6+/+, but not IL-6-/-, mice. These plasma cells fr om IL-6+/+ mice were polyclonal and unable to induce tumour formation in severe combined immunodeficient mice. These data demonstrate that I L-6 is required for pristane-induced hyperplasia of polyclonal plasma cells in mice.