Human IL-6 enhances human lymphocyte engraftment and activation but not human antibody production in SCIDhu PBL mice.

The SCIDhu PBL model of human Ig production was modified by using human interleukin-6 (hIL-6) secreting tumors for continuous hIL-6 production, in vivo. On day one, SCID mice were injected subcutaneously with 200 microliters PBS (control mice), 10(4) SP2/0-Ag14 cells (IL-6+ mice) or 10(4) hIL-6 secreting SP2/0-hIL6.17 cells (IL-6- mice). The mice were reconstituted with human PBMC on day two and immunized with 100 micrograms of tetanus toxoid (TT) on days two and fifteen. Serum hIL-6 concentrations in IL-6+ mice ranged between 2.9 and 38.1 ng/ml by days 26-33. IL-6+ mice had enlarged spleens and lymph nodes (LN). Flow cytometry and histology showed that SCIDhu PBL mouse spleen, LN and peritoneal exudate cells (PEC) contained mostly murine myeloid lineage cells. In addition, many more human B cells, T cells and IL-2R(+)-activated lymphocytes were present in spleen, LN and PEC of IL-6+ mice. Despite enhanced lymphocyte engraftment and activation, by day 14 IL-6+ mice produced up to 6-fold less TT-specific IgG relative to total IgG than either control group. TT-specific and total Ig sera concentrations were equivalent in all three groups on days 26-33. Our results suggest that sustained circulating hIL-6 enhanced human delayed-type hypersensitivity (DTH)-like inflammatory responses with consequential inhibition of TT-specific IgG production in SCIDhu PBL mice.