Role of HLA-DR antigens in antibody production: monoclonal anti-HLA-DR antibodies differ in their ability to directly inhibit B-cell response

Interleukin (IL) 4 counteracts the helper effect of IL2 on antigen-activated human B cells

We tested the effect of interleukin (IL) 4 on the specific IgM antibody response induced by trinitrophenylated-polyacrylamide beads (TNP-PAA) in cultures of human B cells. T cell help was provided by exogeneous IL2. IL4 profoundly suppressed the response to optimal concentrations (50 U/ml) of IL2, with a 50% inhibitory concentration of 6 U/ml. This was due neither to a shift in the kinetics nor to a switch to an IgG response. The production of anti-TNP antibody (as measured by an enzyme-linked immunosorbent assay in the culture supernatant) was inhibited to the same extent as the generation of plaque-forming cells. The effect of IL4 was completely abolished by a neutralizing antibody toward IL4. Kinetic studies showed that IL4 had to be present during the first 48 h of culture to fully inhibit the response. The sequential stimulation of B cells by antigen and by IL2 showed that IL4 does not negatively interfere with signaling through membrane Ig but counteracts the effect of IL2 on antigen-activated B cells.

Antigen-induced and polyclonal B-cell responses in human peripheral blood lymphocyte cultures

This work was designed to delineate the anti-hapten antibody (Ab) response induced by trinitrophenol-polyacrylamide (TNP-PAA) beads from the nonspecific B-cell response which concomitantly occurs in human peripheral blood mononuclear cell (PBMC) cultures. Indeed human PBMC produce consistent amounts of immunoglobulins when cultured at high cell density in the presence of fetal bovine serum, regardless of the presence of antigen. In contrast, the stimulation of such cultures by TNP-PAA leads to an Ab response characterized by the following: cells secreting anti-hapten Ab at a high rate (detected by a plaque-forming cel (PFC) assay); a 10-30 times enhancement in the number of hapten-specific binding cells (detected by a rosette-forming cell (RFC) assay); the production of anti-TNP IgM Ab (detected by an ELISA assay). The anti-TNP response is specifically triggered by the particulate antigen, as shown by the following: The TNP-PAA antigen induces a clear-cut increase in the amount of anti-TNP Ab whereas it only marginally increases that of total IgM. The anti-TNP Ab response is specifically abolished when anti-TNP RFC are depleted from the PBMC preparation before the initiation of the cultures. The anti-TNP Ab response is specifically abolished when PBMC are triggered by TNP-PAA in the concomitant presence of a soluble TNP-protein conjugate. These results demonstrate the ability of polymeric antigens to specifically activate human peripheral blood B cells.

Possible T4-HLA class II interaction as an essential event in antigen-specific helper T lymphocyte-dependent B cell activation

We have previously shown that the interaction between influenza virus-specific helper T lymphocytes and B lymphocytes is HLA class II restricted (Fischer, A. et al., Eur. J. Immunol. 1985. 15: 620). In the present study, we used a panel of antibodies specific for the T4 and HLA-DR molecules to investigate the role of both structures in T-B lymphocyte interaction. Several anti-T4 monoclonal antibodies were shown to block the in vitro antibody production to A/Bangkok influenza virus while they were unable to inhibit the A/Bangkok-induced proliferation of specific helper T cell clones. Some anti-HLA-DR monoclonal antibodies inhibited the antibody production to A/Bangkok, the target of the inhibition being either monocytes or B lymphocytes. The incubation of helper T cell clones with an infra-inhibitory concentration of anti-T4 antibody and of B lymphocytes with an infra-inhibitory concentration of anti-HLA-DR antibody resulted in a mutual enhancement of inhibition. Such synergistic interactions were not observed using combinations of anti-T4 and anti-B membrane structures such as p35 or LFA-1 or anti-HLA-DR and anti-T membrane structures such as T11 or LFA-1. First, these results indicate that the T4 molecule plays an essential role in T-B cell interaction even when it is not absolutely required for T cell proliferation. Second, they strongly suggest that the T4 molecule directly interacts with HLA-DR at the B cell surface. Whether such interaction is required to enhance the stability of T3/T cell receptor-antigen plus HLA class II association or whether T4-HLA-DR may transduce a signal towards B lymphocytes that is required in B cell activation remains unknown.

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.

Monoclonal antibodies against human Ia antigens stimulate monocytes to secrete interleukin 1

The monoclonal antibodies (mAb) DA6.147, DA6.164, and HIG.48 against human Ia antigens, but not the W6/32 mAb against human class I major histocompatibility complex antigens or the anti-monocyte OKM1 and 63D3 mAb, stimulated monocytes to secrete interleukin 1 (IL-1). IL-1 was measured by its property of promoting the production of interleukin 2 (IL-2) by phytohemagglutinin-treated LBRM-33 clone 1A5 cells. IL-1 activity induced by anti-Ia antibodies could be detected 24 hr after initiation of the cultures and reached its highest levels at days 3-4 of culture. Concentrations of 1 microgram/ml or higher of the anti-Ia antibodies induced monocytes to secrete significant levels of IL-1 activity. The anti-Ia mAb induced Ia-bearing but not Ia-negative monocytes to secrete IL-1. Both Ia-positive and Ia-negative monocytes produced IL-1 activity under the stimulus of lipopolysaccharide. It is concluded that the DA6.147, DA6.164, and HIG.48 mAb stimulate secretion of IL-1 by interacting Ia antigens on monocytes. The data support the view that besides serving as restricting elements for recognition of foreign antigens by T cells, Ia antigens may also function as transducer elements.

HLA class II restriction governing cell cooperation between antigen-specific helper T lymphocytes, B lymphocytes and monocytes for in vitro antibody production to influenza virus

To study HLA class II compatibility requirement for in vitro antibody production to influenza virus, semipurified T lymphocytes, B lymphocytes and monocytes from HLA-typed responder donors were used. The presence of the three subpopulations was required for antibody production while a mixture of only two of those was ineffective. When using fresh T lymphocytes which exert an allogeneic suppressive effect and may also exhibit allogeneic helper activity, it was not possible to conclude an HLA class II-linked restriction of T-B cell cooperation although there was a suggestion of it. However, a grown H3 hemagglutinin-specific T cell line (L2), previously shown to be restricted by HLA-DR molecule (DR1) for interaction with antigen-presenting cells and devoid of allogeneic reactivity, exerts an HLA class II-restricted helper activity. This was demonstrated by various combinations of HLA-DR semi-compatible or incompatible B lymphocytes and/or monocytes with L2 T cells. The restriction element was identified as an HLA-DR determined since HLA-DC-compatible, HLA-DR-incompatible B lymphocytes were not helped by L2 T cells. In addition, monoclonal anti-HLA-DR but not anti-HLA-DC antibodies directed to the relevant specificity did inhibit the antigen-specific helper activity. We present evidence that not only T monocyte but also T-B and/or T-B-monocyte interactions are HLA class II restricted.

Production and characterization of a unique monoclonal antibody against human B cells (33.2.1)

A monoclonal antibody specific for a polymorphic antigen on human B cells (33.2.1) was produced and characterized. By flow cytometry, 33.2.1 was found to react with peripheral blood B cells, monocytes, and Epstein-Barr virus (EBV)-transformed B-cell lines, but not with peripheral blood T cells, mitogen-activated T cells, or allo- or autoactivated T cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that 33.2.1 recognizes a noncovalently bound bimolecular complex composed of an alpha chain of about 32 kDa and a beta chain of about 28 kDa. The failure of anti-HLA-DR, anti-Leu-10, and anti-HLA-DC1 to remove the 33.2.1 antigen by sequential immunoprecipitation suggests that 33.2.1 recognizes a distinct molecule rather than a different epitope on either HLA-DR or DS/DC/MB. In T-cell-independent B-cell activation systems, preincubation with 33.2.1 markedly inhibited RNA and DNA synthesis as well as polyclonal Ig production. In contrast, anti-HLA-DR was inhibitory only when it was present throughout the culture, but not when it was used for preincubation. Anti-Leu-10 led to only moderate inhibition. These results suggest that 33.2.1 recognizes a unique Ia-like antigen critical for B-cell activation.

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

It is shown that the anti-trinitrophenyl (TNP) response of human B cells to trinitrophenyl polyacrylamide beads (TNP-PAA) is monocyte dependent. This response is abolished by extensive adherent cell depletion and restored by the addition of monocytes. The optimal response is obtained with 3% monocytes, higher numbers being suppressive. Supernatants from muramyl dipeptide (MDP)-activated monocytes can restore the response of monocyte-depleted preparations even when cells are cultured at suboptimal concentration. A partially purified preparation of interleukin (IL-1) has a comparable restorative ability. The following arguments suggest that monocytes do not function as antigen-presenting cells for this particulate antigen: (i) antigen-pulsed monocytes induce neither an anti-TNP response nor a specific T-cell proliferative response; (ii) allogeneic monocytes function as well as autologous monocytes to restore the response of nonadherent cells; (iii) HLA-DR-negative cells from the human leukemia cell line K562 can replace monocytes for this response. Monocyte supernatants do not replace T cells for the response of B-enriched lymphocytes, showing that T cells are directly involved in B-cell activation.

Helper T cell activation for the human B cell response to trinitrophenylated polyacrylamide beads: involvement of the T4 antigen

The monoclonal antibody (mAb) OKT4A (but not OKT4) inhibits the in vitro antibody response of human peripheral blood mononuclear cells. The target of OKT4A mAb is the helper T cell, as the helper cells for the antibody response to trinitrophenylated polyacrylamide beads (TNP-PAA) are exclusively in the T4 subset. The OKT4A mAb is still suppressive when the anti-TNP response of cultures of monocyte-depleted cells is supported by purified interleukin 1. Both the OKT4A mAb and anti-DR mAb suppress the non-specific T cell proliferation in the cultures leading to the in vitro mAb response. A parallel inhibition is observed for the autologous mixed lymphocyte reaction, the nonspecific B cell response, but the T cell response to mitogens is not affected. These results suggest that the recognition of self major histocompatibility complex class II determinants by the T4 molecule plays a major role in the activation of T helper cells for antibody production to this particulate antigen.

Prostaglandin E2 regulation of human specific B-cell response: interaction with a monocyte product

The effect of exogeneous prostaglandin E2 (PGE2) on the specific plaque-forming cell (PFC) response in cultures of non-adherent human peripheral blood mononuclear cells (PBM) was tested. When added on Day 2 of the cultures PGE2 inhibits the induction of the PFC response, and the maximum inhibition (50%) is obtained with 300 nM PGE2. When PBM are cultured during the first 24 hr with the same concentration of PGE2 their PFC response is enhanced and the target of this enhancement is a T cell. When PGE2 is added on Day 0 it does not affect the response, probably because of a balance between these two opposing effects. However, in the latter conditions a prostaglandin-free monocyte supernatant can render PGE2 suppressive. The monocyte supernatant acts by inhibiting the stimulatory effect after the interaction between PGE2 and T cells. Thus the effect of PGE2 depends on its time of action and on the concomitant production of a nondialyzable factor by monocytes.

Differential effect of monoclonal anti-DR antibody on monocytes in antigen- and mitogen-stimulated responses: mechanism of inhibition and relationship to interleukin 1 secretion

A differential role for DR antigens on monocytes in antigen-stimulated as opposed to mitogen-stimulated human lymphocyte responses has been observed. A monoclonal anti-DR antibody used to treat monocytes caused inhibition of antigen-induced T-cell responses and of T-cell-dependent B-cell responses. However, anti-DR antibody treatment of monocytes did not inhibit mitogen-induced responses. Anti-DR treatment of monocytes did not induce suppression, as antigen-induced responses could be reconstituted with untreated monocytes. Anti-DR treatment of monocytes did not merely block interleukin 1 (IL-1) secretion since addition of IL-1 could not restore antigen-induced responses. Monoclonal anti-DR antibody did not directly inhibit monocyte secretion of IL-1. DR-negative monocytes, selected by antibody and complement, could not present antigen, even though they were capable of secreting IL-1. Thus, this monoclonal anti-DR antibody sterically blocks antigen presentation by monocytes without induction of suppression or inhibition of IL-1 secretion. Monocyte DR antigens appear essential for stimulation of antigen-induced responses, but DR antigens on monocytes may not be essential for mitogen-stimulated responses and do not appear to be related to the ability of monocytes to secrete IL-1.

Effect of hydrocortisone on the in vitro human antibody response: interaction with monocytes and prostaglandins

The specific plaque-forming cell response induced by trinitrophenyl polyacrylamide beads in cultures of nonadherent human peripheral blood mononuclear cells (PBM) is resistant to the inhibitory effect of hydrocortisone (HC). Previous results showed that low concentrations (up to 10(-7 M) of HC inhibit the same response in cultures of unfractionated human PBM. It is shown that the addition of 5-10% monocytes to nonadherent PBM renders their response HC-sensitive. One mechanism of the interaction between HC and monocytes is the potentiation of prostaglandin E2-mediated suppression by HC, which can be demonstrated in vitro and after in vivo administration of HC. However, interaction with a non-prostaglandin-mediated suppression by monocytes should be involved, particularly with high (10(-6) M) concentrations of HC.