Dextran sulfate-mediated enhancement of mitogen-induced B-cell proliferation

Glial cells as suppressor cells: characterization of the inhibitory function

Rat retinal glial cells (Müller cells) profoundly suppress antigen-driven activation, as well as the subsequent interleukin-2 (IL-2)-dependent expansion of autoimmune and conventional-immune syngeneic T-helper lymphocytes, through a contact-dependent mechanism. Characterization of this inhibitory function showed that some activation parameters of autoimmune T-helper lymphocytes specific to the retinal soluble antigen, responding to antigen presented on syngeneic antigen-presenting cells, were differentially affected by coculture with Müller cells. In contrast to endogenous IL-2 production, IL-2-receptor generation and proliferation, the production of interleukin-3 and of interferon-gamma were not inhibited. Inhibition of IL-2-supported proliferation of cells which had already generated the IL-2 receptor was markedly potentiated in the presence of the specific antigen, in a dose-dependent manner. The extent of inhibition was proportional to the number of Müller cells in the culture. The suppression appeared not to involve a major histocompatibility complex (MHC) Class II-related interaction and could act across allogeneic and even xenogeneic barriers. Inhibition affected normal lymphocytes, including primed T cells responding to antigen or to IL-2, unprimed spleen cells responding to the T-cell mitogen concanavalin A (Con-A) and, to a lesser extent, unprimed spleen cells responding to the B-cell mitogen bacterial lipopolysaccharide (LPS). Several permanently transformed cell lines of mouse, rat and human origin were not affected. These results may suggest participation of organ-resident cells in regulation of locally occurring immune processes.

Clonal analysis of the synergistic mitogenic effect of lipopolysaccharide and dextran sulphate on B cell activation, growth, and differentiation into Ig-secreting cells

Splenic B cells of BALB/c mice were stimulated in vitro either with lipopolysaccharide (LPS), dextran sulphate (DxS), or with both LPS and DxS. The absolute frequency of B cells that differentiate into clones of immunoglobulin (Ig)-secreting cells upon activation with these mitogens was determined by means of limiting dilution analysis. Determination of the number of Ig-secreting cells in DxS-stimulated cultures with the protein A plaque assay proved to be difficult because of the anti-complementary activity of DxS. Therefore, we assayed the number of Ig-secreting cells with a reverse ELISA-plaque assay. This assay is complement-independent and is at least as sensitive as the protein A plaque assay. The results showed that LPS, DxS, and the combination of LPS and DxS stimulate 1 in 27, less than 1 in 500 and 1 in 15 nucleated spleen cells of BALB/c mice to proliferation and differentiation into a clone of Ig-secreting cells, respectively, indicating that these mitogens have a synergistic effect on B cells at the precursor cell level. Analysis of the clone size of the activated B cells showed that the combination of both mitogens also caused a larger clone size. Thus, the synergistic effect of LPS and DxS that was previously observed in mass cultures is due to two separate effects. Quantitatively most important, however, is that more precursors are activated by the combination of the two mitogens.

Role of adherent cells in dextran sulfate-mediated enhancement of mitogen-induced B-cell proliferation

We have studied lipopolysaccharide (LPS)-induced proliferation in the rat and have found that the addition of the compound Dextran sulfate (DxS), which itself is not mitogenic, to LPS stimulated cultures results in significant enhancement of cell division. A "DxS-free" supernatant from DxS stimulated spleen cell cultures is able to substitute for DxS in stimulatory activity. This supernatant possesses interleukin 1 (IL-1) activity, however, the addition of purified recombinant IL-1 to LPS-stimulated cultures does not result in augmentation of proliferation. A DxS-free supernatant from DxS stimulated adherent cells is also able to substitute for DxS in stimulatory activity. The active molecule(s) present in the adherent cell-derived DxS-free culture supernatant appears to be distinct from classical IL-1.