Interleukin 1 can replace monocytes for the specific human B-cell response to a particulate antigen

Glucocorticosteroid-dependent synergy between interleukin 1 and interleukin 6 for human B lymphocyte differentiation

In order to analyze the effects of interleukin (IL) 6 on human in vitro Ig production B lymphocytes were activated by Staphylococcus aureus Cowan strain I (SAC) in the presence of low concentrations of IL2 (1 U/ml) and dexamethasone (10(-7) M). Previously we showed that this model of B cell response is completely monocyte dependent. We here demonstrate that, under these experimental conditions, IL6 is able to replace monocytes and stimulate Ig production provided IL1 is also present. Dose-effect curves show that these two monokines act synergistically. This synergy is demonstrable only in the presence of dexamethasone, when B lymphocytes are activated (by SAC) and when T cell help (provided by IL2) is present. It results in the production of both IgM and IgG. Both IL1 and IL6 have to be present during the first 48 h of culture to exert an optimal effect. These results show that IL6 may act on early (as well as on late) stages of normal B lymphocyte differentiation. Moreover, glucocorticosteroids potentiate the synergistic effect of IL1 and IL6 on their B lymphocyte target, an effect comparable to that exerted on hepatocytes.

Functional effects of epidermal cell culture supernatants (ECCS) on human B-cell activation

Epidermal cells (EC) were cultured without stimulation and the effect of these EC culture supernatants (ECCS) on human in vitro B-cell response was determined. Supernatants obtained between Days 5 and 7 were able to replace monocytes in the antibody response to the particulate antigen trinitrophenyl-polyacrylamide (TNP-PAA). These results were obtained when highly monocyte-depleted cultures (less than 0.5% peroxidase-positive cells) were used and were reproduced with supernatants from several different EC cultures. ECCS could not substitute for T cells in the T-dependent response to TNP-PAA. They contained an interleukin 1 (IL-1) activity but no interleukin 2 or B-cell growth factor (BCGF) activities. We tested the effect of ECCS on the proliferative response of highly monocyte-depleted B cells cultured at low cell density costimulated with anti-u antibody and BCGF. ECCS had no BCGF-like activity of its own but did potentiate the effect of BCGF. Thus EC cultures produce IL-1-like factor(s) which act directly on the early stages of B-cell activation.

Production of human--human hybridomas secreting antibody to sheep erythrocytes after in vitro immunization of peripheral blood lymphocytes

This report describes the formation of human hybridomas after in vitro immunization of peripheral blood lymphocytes (PBL) with an antigen and fusion of the stimulated lymphocytes with a HAT-sensitive human myeloma cell line, RPMI 8226. PBL were stimulated in vitro with sheep erythrocytes (SRBC) plus fresh human serum. PBL of some donors produced anti-SRBC antibody when they were cultured at 2 X 10(6) cells per well in a 24-well plate with the antigen plus fresh human serum for 7 days. Although lymphocytes of some donors were "low-responders" under the above conditions, they responded to SRBC when they were cultured with not only the antigen plus fresh human serum but also with the culture supernatant obtained after phytohemagglutinin (PHA) stimulation of a mixture of PBL from two donors (MLC-PHA sup). The cells sensitized by this procedure were fused with RPMI 8226 cells. Hybrids secreting IgM or IgG anti-SRBC antibodies were obtained. Additionally the ratio of total IgG-producing hybridomas to IgM-producing ones was higher when the MLC-PHA sup was used at the time of the in vitro immunization.

Differentiation factors for human specific B cell response

Nonspecific T cell factors produced by lectin-activated human peripheral blood lymphocytes (PBL) were used to restore the T-dependent B cell response to trinitrophenyl-polyacrylamide (TNP-PAA). Preincubation experiments with the particulate antigen TNP-PAA and/or a soluble TNP-protein conjugate show that a first specific signal provided by the antigen and nonspecific lymphokines sequentially acts on B cells. By gel filtration the T cell-replacing factor (TRF) activity is present in the 30-15-kDa fraction of T cell supernatants and is associated to interleukin 2 (IL2). However, absorption of IL2 does not abolish the TRF activity. Moreover, chromatofocusing of this 30-15-kDa material allows the obtaining of an IL2-free fraction containing a differentiation factor (with an isoelectric point of 5.7 +/- 0.2). The ability of this fraction to restore the anti-TNP response is manifest in the presence of a 50-kDa B cell growth factor. This latter, prepared by a combination of absorption on concanavalin A-Sepharose and gel filtration, was IL2 free and unable to support the anti-TNP response. We thus directly demonstrate that in the absence of IL2 three separate signals (the antigen, T cell-derived growth and differentiation factors) are involved in human-specific B cell response.

Suppressor T cell induction by soluble OKT3 antibody does not require cross-linking of the T3 molecule

The monoclonal antibody OKT3 can induce T suppressor cells of the in vitro antibody response when used at concentrations as low as 10 ng/ml and in cultures containing as few as 4% OKT3-pretreated T cells. These suppressor cells are radioresistant, cyclosporin sensitive and belong to the T4 as well as the T8 subpopulations. In contrast with the mitogenic effect of OKT3 the suppressor activity can be induced and expressed in highly monocyte-depleted cultures. Moreover F(ab')2 fragments of OKT3, although not mitogenic, are able to induce suppressor cells. Thus cross-linking of the T3 molecule (such as that realized when intact OKT3 IgG and monocytes are present) is not required to induce suppressor cells among resting normal T cells.