In vitro sensitization of human T lymphocytes to hapten (TNP)-conjugated and non-treated autologous cells is restricted by self-HLA-D

In the murine syngeneic mixed lymphocyte reaction, one T cell subset replicates in the presence of B cells or macrophages and replication is inhibited by simultaneous presence of both stimulator cells

The murine T-non-T cell syngeneic mixed lymphocyte reaction has been examined to determine whether B cells and macrophages stimulate the same or different subpopulations of T cells. By using experiments in which replicating T cells were suicided, we found that the two different stimulators caused replication of what appears to be the same subset(s) of T cells. Since B cells and macrophages carry the same stimulating antigens (class II plus mls or others), one would expect them to stimulate the same T cell subpopulations were it not that they have been reported to stimulate two different subpopulations in humans. When B cells and macrophages were simultaneously used as stimulators, diminished T cell replication occurred. We have found the reduced response is not attributable to exhaustion of culture nutrients or to displacement of the response peak. Other possibilities to account for this marked reduction have been discussed from the viewpoint of suppression emanating from macrophages and/or T cells.

A monoclonal antibody that blocks class II histocompatibility-related immune interactions

Previous studies using conventional hetero- or isoantisera have indicated the involvement of class II (Ia) molecules in presentation of soluble antigen by monocytes to inducer T lymphocytes, stimulation of inducer T cells in MLR, and recognition of Ia-bearing target cells by cytotoxic T lymphocytes (CTL). The experience in using monoclonal anti-Ia reagents capable of blocking these phenomena in the human system is limited. Recently, however, we have characterized a lytic IgG2a monoclonal antibody, 9-49, that binds to functionally significant class II molecules. This antibody blocks (in the absence of complement): (1) specific binding of peripheral blood lymphocytes (PBL) to antigen-pulsed monocyte monolayers, (2) proliferation of PBL in response to soluble antigen (tetanus toxoid or mumps) or cell surface class II antigen stimulation in allogeneic or autologous MLR, (3) proliferation of cloned T4+ (inducer) lymphocyte cell lines to class II antigens, (4) generation of cytotoxic lymphocytes during allogeneic MLR, and (5) recognition (and killing) of class II-bearing target cells by T4+ CTL clones. Proliferation and CTL activity of a T8+ clone is unaffected by the 9-49 antibody. These results indicate the usefulness of this monoclonal reagent in studies evaluating the functional role of Ia molecules in immune recognition phenomena.

Plaque-forming cells in man. III. Generation of plaque-forming cells in allogeneic in vitro cultures of HLA-D/DR-incompatible B and T lymphocytes

We have investigated the ability of allogeneic, irradiated T lymphocytes to induce proliferation and immunoglobulin (Ig) secretion in untreated peripheral blood B lymphocytes. Non-mitogen-activated co-cultures of isolated T and B lymphocytes from selected, full-house HLA-A,B and D/DR antigen-phenotyped donors were reconstituted in a ratio of 4:1. Proliferation was assessed on day 5-6 of culture by the 3H-thymidine incorporation technique, and the Ig secretion was monitored on day 6 with a protein A plaque-forming cell (PFC) assay. B lymphocytes were able to differentiate into PFC, and the number of plaques was significantly higher in cultures of cells with two HLA-D/DR antigen incompatibilities than in those sharing one antigen. In cultures of peripheral blood lymphocytes with no HLA-D/DR antigen difference, only a few PFC developed. HLA-A and B antigens had no influence on the response. Further, monocytes were not an absolute requirement for allogeneic activation of B cells. Sonicated T cells and culture supernatants from allogeneic T- and B-cells cultures were not able to induce PFC formation in B lymphocytes. Our results indicate that the PFC response obtained in non-mitogen-activated cultures of allogeneic T and B lymphocytes is dependent on HLA-D/DR disparity or on genes encoded in the HLA-D/DR region.

Cell-mediated PPD-specific cytotoxicity against human monocyte targets: evidence for restriction by class II HLA antigens

Human Purified Protein Derivative of tuberculin- (PPD-) specific cytotoxic cells have been detected in cultures of peripheral blood mononuclear cells stimulated for 6 days with PPD. These cytotoxic cells are demonstrated by their ability to lyse PPD-pulsed autologous monocyte target cells, but not unpulsed targets. In a series of checkerboard experiments each involving 3-5 randomly combined donors, effector cells from 35 donors have been tested in autologous and 130 allogeneic combinations. Analysis of results from the pooled allogeneic combinations reveals that HLA-B - and even more pronounced HLA-DR - antigen sharing correlates positively to high lysis. No effect of HLA-A antigen sharing is found. A more detailed analysis shows that the effect of HLA-B sharing may be fully accounted for by HLA-B-DR linkage disequilibrium. The results thus indicate that cell-mediated PPD specific cytotoxicity is HLA-restricted. Further, the correlation to HLA-DR sharing indicates that the restriction element in this system in all probability is a class II antigen.

Monoclonal antibody analysis of responder and stimulator cells in the human autologous mixed lymphocyte reaction

Responder and stimulator cell subpopulations in the autologous mixed lymphocyte reaction (AMLR) were determined with the OK series of monoclonal antibodies. Mitomycin-C-treated, monocyte-enriched cell populations were used as stimulator cells in the AMLR. Treatment of these monocytes with either OKM and/or OKI monoclonal antibodies and complement resulted in a marked loss of ability of these cells to act as stimulators in the AMLR. Removal of OKT3+ and OKT4+ cells diminished the proliferative responses of AMLR cultures. Interaction of T cells with autologous monocytes resulted in generation of cells capable of suppressing both MLR and AMLR cultures. The suppressor activity of these cells was diminished by treatment with OKI , OKT4 or OKT8 monoclonal antibodies. No cytotoxic activity to autologous or allogeneic monocytes was observed. Additional studies showed an increased number of OKT9 + and OKI + as well as OKT8+ T cells in the AMLR responder cell population. This study indicates that cultures of T lymphocytes with autologous monocytes yield T cell subset(s) which suppress MLR and AMLR reactivity.

Studies of autologous mixed lymphocyte reactions in patients with systemic lupus erythematosus

The autologous mixed lymphocyte reaction (AMLR) measures the proliferative response of peripheral blood T cells to surface antigens of non T cells. The AMLR of SLE patients with active or inactive disease either with (13) or without (6) immunosuppressive treatment was low compared with age and sex-matched controls, confirming previous reports. Only one patient with inactive, untreated SLE and one with drug induced lupus (procainamide) showed normal AMLR. Autologous reactivity was also reduced in 2 patients without treatment who presented with clinically complex disease syndromes, including primary biliary cirrhosis, or polyarteritis nodosa, together with Sjögren's syndrome and serological evidence of lupus. The AMLR could not be increased by changing the ratio of responder to stimulator cells. Patients with decreased AMLR also showed a decreased response to phytohemagglutinin which suggested a general depression of T cells. There was no correlation between the decreased AMLR and age, clinical features or anti-DNA antibody levels of the patients. In allogeneic mixed lymphocyte reactions (MLR) it was shown that non-T cells from SLE patients were poorer stimulators of allogeneic T cells than normal cells, and T lymphocytes from SLE patients were poorer responders to allogeneic non-T cells than were normal T cells. Both effects were much more marked in patients with active disease than in those with inactive SLE. This suggests a defect in both responder and stimulating cell populations in SLE.

Activation of human alloreactive cytotoxic precursor T lymphocytes

The requirements for allogeneic T-cell activation have been studied in experiments with T and/or B cells as stimulator. Although target determinants (TDs, defined by CTL effectors in CML) are present on B and T cells used as target cells, this study indicates that TDs are functionally different when expressed on B and T cells used as stimulator cells, as only B cells can activate CTL precursors. Further, the study confirms that inducing TDs and strong lymphocyte-activating determinants (LADs, defined by proliferation in MLC) can be distinct structures found on two different stimulator B cells. The study suggests that binding of cytotoxic precursor T cells to TDs per se does not allow any detectable activation or start of proliferation and differentiation but requires another function of the stimulator cells in the non-T-cell compartment. The nature of this function is unknown, but it is the background for the first signal received by the TD-specific clones of CTL precursors, resulting in the expression of growth receptors for T-cell growth factor or interleukin 2 which is the second signal necessary for clonal expansion and differentiation.

Sensitization of human lymphocytes in vitro. Kinetics and specificity of the response to hemocyanins

In vitro primary sensitization of human peripheral blood T-cells to hemocyanins was detected during a 12-14 day culture period with antigen (KLH or HCH)-pulsed macrophages. Primed T-cells proliferate in secondary culture (2-3 days) when restimulated with antigen presented by macrophages. The kinetics of primary sensitization and secondary responsiveness are interrelated and are dependent on the antigen doses employed. Antigen-induced proliferation of cells sensitized in vitro is identical to proliferation of T-cells from immunized donors in terms of antigen specificity and the clonal nature of the response to antigen. Through the use of thymidine suicide techniques, distinct populations of cells responding to KLH or HCH can be demonstrated using cells from actively immunized donors or cells that have been sensitized in vitro to both hemocyanins.

HLA-restricted responses to M and N determinants in the primed lymphocyte test

We have studied the role of MNSs determinants in the primed lymphocyte test (PLT). The data demonstrate that incompatibility associated with the M or N antigens causes HLA-restricted proliferative responses in PLT. Responses to the M or N determinants required the presence of the same HLA-A antigen(s) on both the stimulator and the responder cells. No effects of S or s incompatibility were observed in this test. This is the first report of lymphocyte proliferative responses to "minor" alloantigens that require corecognition of the MHC determinants. These observations suggest possible new biological functions of these blood group antigens.

Endothelial cell presentation of antigen to human T cells

Activation of human T cells requires presentation of antigen by Ia (HLA-DR in man) bearing cells of the mononuclear phagocytic series (macrophages, MO, and more recently Langerhans cells, dendritic cells, and vascular endothelial cells. Since T cells must cross endothelial barriers to enter extravascular tissues during immune reactions, we investigated the role of endothelial cells in antigen presentation. Endothelial cells were cultured from human umbilical veins and identified by classic morphology and specific markers (factor VIII related antigen, and so on). Antigen-pulsed endothelial cells were used to present antigen to MO-depleted human T cells; activation was assessed by 3H-thymidine uptake. The HLA-DR compatible endothelial cells were as effective as MO in reconstituting MO-depleted T-cell responses. The endothelial cell reconstituted responses were antigen specific, HLA-DR restricted, and blocked by monoclonal antibodies to HLA-DR framework structures. Moreover, the T-cell responses were clonal with respect to HLA-DR. A monoclonal antibody completely eliminated MO reconstitution of the MO-depleted response without diminution of endothelial cell reconstitution of the same response. Fibroblasts and smooth muscle cells cultured from the same umbilical veins could not reconstitute the MO-depleted T-cell response. These data indicate that endothelial cells play an important and distinctive role in lymphocyte triggering.

Inhibition of in vitro nickel sulfate reaction by anti-HLA-D/DR antisera. Lack of demonstrable suppressor cells in peripheral blood in nickel unresponsiveness in man

A nickel sulfate induced lymphocyte blast transformation reaction in vitro was specifically inhibited by anti-HLA-D/DR antisera, which indicates the requirement of HLA-D/DR antigens in cellular cooperation. Macrophages are effective antigen presenting cells in the in vitro nickel reaction and this step could be the site of an HLA-antigen function in the recognition of "self." It was shown that macrophages of an HLA identical, healthy sibling could offer proper "help" to macrophage-depleted lymphocytes of the nickel allergic subject in evoking a nickel reaction. Thus, in this respect, the function of macrophages in nickel allergy is not different from that in a nickel-unresponsive state. The nickel unresponsiveness in healthy subjects is probably not due to specific suppressor cells because HLA identical lymphocytes from the healthy siblings could not suppress the nickel induced blast transformation of the nickel allergic siblings. This suggests that a deletion of sensitized clones in the periphery is the more probable mechanism of unresponsiveness in healthy subjects.

HLA-DR antigens induce proliferation and cytotoxicity of T cells against haptenated (TNP and FITC) self structures

Antisera directed against the heavy, the light, or reactive against the complex of both chains of HLA-DR antigens strongly inhibited proliferation of T cells induced by TNP- or FITC-labeled autologous cells when added at initiation of the cultures, but not 72 h later. T cells from cultures treated with the anti-DR sera were unresponsive to interleukin-2 (IL-2). Nonetheless, the anti-DR sera did not inhibit proliferation of T cells that had already acquired sensitivity to IL-2. The DR antibodies abrogated the synthesis of IL-2 induced by both TNP-and FITC-conjugated autologous cells. Treatment of TNP-and FITC-labeled autologous cell cultures with the four different types of anti-DR sera significantly inhibited the induction of cytotoxic T cells. However, DR antibodies added at the effector phase of cytotoxicity assays did not inhibit the cytotoxic activity. Effector T cells from cultures treated with the anti-DR sera were unresponsive to IL-2 and addition of IL-2 to these cultures did not restore the cytotoxic activity. In contrast, effector T cells from cultures performed in the absence of the anti-DR sera proliferated to Il-2 stimulation and addition of IL-2 to these cultures significantly increased the generation of killer cells specific for hapten-labeled self structures. From these results we concluded the following: (1) Both the heavy and the light chains of Dr antigens participate actively in the activation of T cells by rendering resting T cells sensitive to IL-2 and by inducing production of the growth factor in TNP-and FITC-conjugated autologous cell cultures. (2) The heavy and light chains of the DR antigens play an essential role in the induction of cytotoxic T cells specific for hapten-labeled self structures, most likely by enabling cytotoxic T cells to respond to Il-2 and by inducing the IL-2 producer T cells to synthesize the growth factor.

Studies on human epidermal Langerhans cells III. Induction of T lymphocyte response to nickel sulphate in sensitized individuals

Human epidermis from nickel sensitive patients was separated from dermis by means of a suction blister device and dissociated with trypsin. The epidermal cell suspensions obtained contained 3--5% Langerhans cells as judged by immunofluorescence staining of the cells with a rabbit anti-DR antiserum. The epidermal cells were co-cultured with purified autologous T lymphocytes with or without nickel sulphate. A strong proliferative T lymphocyte response to nickel sulphate was obtained provided epidermal cells were also present. Pretreatment of the epidermal cells with anti-DR antiserum abolished or greatly reduced the response. These data indicate that epidermal cells are able to present nickel sulphate to T lymphocytes in an immunogenic way. Since the responsible cells were DR antigen positive, it is highly probable that the cells responsible for these functions are the Langerhans cells.

HLA-D/DR restriction of macrophage-dependent antigen activation of immune T lymphocytes: cross-reacting allogeneic HLA-D/DR may partly substitute for self HLA-D/DR

Optimal proliferative response of T lymphocytes to purified protein derivative of tuberculin (PPD) in vitro requires that antigen be presented by autologous macrophages or allogeneic macrophages sharing HLA-D/DR determinants with the T cell donor. In some cases, however, T cells may respond to a limited extent to PPD in association with macrophages expressing different HLA-D/DR determinants. In this paper experiments are presented where various combinations of T cells and HLA-D/DR disparate macrophages were stimulated with PPD. We often found a stronger PPD-specific response in HLA-D/DR-incompatible combinations in which the macrophages carried HLA-DR antigens known from serological studies to be cross-reactive with those of the T cell donor than in combinations in which this was not the case. Thus, the cross-reactions detected by serology may sometimes be reflected on a functional level in T lymphocyte/macrophage cooperation.

Studies on human epidermal Langerhans cells. I. Allo-activating and antigen-presenting capacity

Human epidermis was separated from dermis by means of a suction blister device and dissociated with trypsin. The epidermal cell suspensions obtained contained 3--5% Langerhans cells as judged by immunofluorescence staining ot the cells with a rabbit anti-DR antiserum. The epidermal cells were co-cultured with purified allogeneic T cells and with autologous T cells with or without PPD of tuberculin. A strong T-cell response to allogeneic epidermal cells was obtained, as was a strong T-cell response to PPD, provided autologous epidermal cells were also present. Pre-treatment of the epidermal cells with anti-DR antiserum plus complement abolished both these responses. These data indicate that epidermal cells are able to substitute for macrophages both in the allo-activating and in the antigen-presenting function. Since the responsible cells were DR-positive, it is highly probable that the cells responsible for these functions are the Langerhans cells.

Human T cell response to Herpes simplex virus antigen in vitro

Herpes simplex virus type I antigen (HSV-Ag) added to T cells from individuals with clinical history of recurrent herpes labialis causes a proliferative response in vitro. This T cell response requires presensitization of the responding cell donor and will occur only in the presence of adherent cells (macrophages). The intensity of the response is closely related to the number of adherent cells present, being optimal at a ratio of 10:1 between T cells and adherent cells. Preliminary studies also indicate that the response to HVS-Ag is restricted by the HLA-D/DR determinants of the T cell donor.

HLA-D-restricted antigen activation of sensitized T lymphocytes: studies on the ability of HLA-D/DR-expressing B lymphocytes to substitute for macrophages in antigen activation

The proliferative response of sensitized human T lymphocytes to purified protein derivative (PPD) and to trinitrophenyl (TNP)-conjugated autologous cells in vitro is restricted by self HLA-D/DR determinants. Here we report that the PPD-specific response is strictly related to the content of phagocytosing cells (macrophages, Mphi) in the cultures and that an optimal PPD response occurred at a T/Mphi ratio between 10:1 and 5:1. B-cell-enriched suspensions, which also express the HLA-D/DR determinants, were not able to replace the macrophages in this HLA-D/DR-restricted response. On the other hand, TNP-treated similarly prepared B cells were in most instances effective in inducing a secondary TNP-specific response of in vitro-sensitized T cells.