Els R. de Groot

Human mononuclear leukocytes produce a growth factor (HGF) for hybridoma and plasmacytoma cells. HGF has recently been proven to be identical to IFN-beta 2, 26-kDa protein and BSF-2. HGF can be quantitated in a proliferation assay with the HGF-dependent hybridoma cell line B13.29. By selection of an extremely sensitive variant of this cell line, we were able to measure HGF production of single cells. Limiting dilution analysis of the producing cells in combination with size, density and adherence characteristics showed that HGF is produced by monocytes and not by lymphocytes. There was no need for the monocytes to be stimulated but the cells did require the presence of serum. This serum requirement could be met by purified bovine serum albumin, but not by other proteins like ovalbumin or human gamma-globulin. HGF production in vitro by monocytes starts after 2 h of incubation and is completed within 24 h.

C. luciliae are hemoflagellates nonpathogenic for man and easy to culture. They have a giant mitochondrion, in which the mitochondrial DNA is concentrated in a single large network, the kinetoplast. When used as a substrate for the indirect immunofluorescence technique, studying sera from patients with SLE, we could demonstrate a very good correlation between this test and the Farr assay for the demonstration of antibodies to double-stranded DNA. Although the sensitivity of both techniques is on the same order of magnitude, the IF technique has the following advantages over the Farr assay. It is easy to perform in laboratories equipped for autoimmune serology. It possesses an intrinsic check on the immunoglobulin character of the DNA-binding activity. It allows one to determine the Ig classes and subclasses of antibodies to DNA. It permits study of complement fixation to antibodies without interference of Clq fixation to DNA or anticomplementarity of the serum. There is an absence of interference with antibodies to single-stranded DNA.

Human monocytes produce a number of soluble mediators involved in regulation of inflammation and lymphocyte growth and differentiation such as interleukin 1 (IL 1) and tumor necrosis factor. Recently, the cDNA of another monocyte-derived factor, interleukin 6 (IL 6), was cloned. Herein we show that purified E. coli-derived recombinant IL 6 (rIL 6) is as active as IL 1 in the thymocyte assay. In addition, IL 1 and IL 6 synergize strongly in stimulating thymocyte proliferation. Another property shared by IL 1 and IL 6 is their pyrogenicity. Human rIL 6 induces a monophasic fever after i.v. injection into rabbits. Together with the observation that IL 1 induces IL 6 in a variety of cells including thymocytes, our data suggest that IL 6 is involved in many of the pleiotropic effects of IL 1.

Monoclonal antibodies (mAb) directed against the CD3 (T3), antigen are able to induce proliferation in resting human T lymphocytes. T cell proliferation only occurs in the presence of monocytes that carry the proper Fc receptor for the mAb used. To further analyze the role of the Fc portion of anti-CD3 mAb in proliferation induction, we isolated, starting from a gamma 1 anti-CD3-producing hybridoma, four heavy-chain isotype switch-variant antibody-secreting clones, producing gamma 2b, gamma 2a, epsilon and alpha, respectively. All variant antibodies recognize the CD3 antigen as determined by immunoprecipitation and cross-blocking experiments. With this series of isotype variant antibodies we were able, in proliferation induction experiments, to confirm the Fc receptor polymorphism for murine IgG2a, IgG2b and IgG1 on human monocytes. Moreover, we found that all 30 donors tested responded to the IgE anti-CD3 antibody, while no IgA responders could be identified. The induction of proliferation by the IgE variant antibody does not require the 72-kDa Fc receptor which is responsible for the interaction with mouse IgG2a. Nonresponsiveness to the IgG1 antibody, but not to the IgG2b or IgA variant antibodies, could be overcome by the addition of exogenous interleukin 2 to the cultures. When the switch-variant antibodies were used to induce IgM synthesis in peripheral blood mononuclear cells only low IgM synthesis was found, with the exception of the IgE variant, which induced excellent T cell help for IgM production.