Long-term maintenance of HLA-D restricted T cells specific for soluble antigens

At least five antigenic epitopes on the streptokinase molecule are recognized by human CD4+ TCR alpha beta+ T cells

The streptokinase molecule (415 AA) was cleaved at methionine 237, 347 and 370 yielding four polypeptide fragments. Human HLA-class II restricted streptokinase-specific T cell clones and cell lines (CD2+, CD3+, CD4+, CD8-, TCR alpha beta+, TCR gamma delta-) recognized antigenic epitopes on all four fragments AA 1-236, AA 238-346, AA 348-369 and AA 371-415. T cell clones recognizing fragment AA 1-236 were restricted by at least two different HLA-class II elements, this indicating that more than one antigenic epitope can be recognized on this fragment. In addition, two streptokinase-specific T cell clones recognized only the intact molecule and none of the molecular fragments. These two clones probably recognized an antigenic epitope including one of the methionine residues used for molecular cleavage. We conclude that T cell proliferative responses to streptokinase are determined by recognition of at least five different antigenic epitopes distributed along the entire streptokinase polypeptide chain.

Immune response: tissue specific T-lymphocytes

The lymphatic system forms a 'blind' plexus of vessels that in general are found in tissue which has an inherently high replicative capacity. It is this system that is responsible for the rapid deployment and circulation of tissue-specific T-lymphocytes for the inspection of cell-surface aberrations within the tissue. The presence of tissue-specific T-lymphocytes explains why 90% of lymphocytes are found outside the lymphatic system and why they migrate in a selective manner. The tissue-specific T-lymphocyte is considered to express a common lymphocyte cell surface pattern, the homotype, and a tissue-specific cell-surface pattern, the histotype which may involve MHCA and mHCA. It is the histotypic pattern that is responsible for the tissue specificity of the tissue-specific T-lymphocyte. The presence of tissue-specific T-lymphocytes does pose problems for the immune system. If different tissue-specific T-lymphocytes met within a particular tissue, 'lost' lymphocytes, an immune response will be generated against the intruder (lost lymphocyte), and the intruder will not be able to recruit other immunocompetent cells in that tissue. This immune reaction is an attempt to change the histotypic pattern of the intruder. This situation would explain the autologous immune response. This response however is suppressed in the systemic system by immunosuppressive compounds from the liver. It is only in the tissues that the tissue-specific T-lymphocytes are released from this suppression, in order to initiate immune reactions against aberrant cell-surface patterns.

Characterization of skin-infiltrating lymphocytes in patients with psoriasis

In this study, skin-infiltrating cells in psoriasis patients were characterized in biopsies from both involved and uninvolved skin. Histologic examination of biopsies showed the presence of both CD4+ and CD8+ T cells and the lack of B lymphocytes. Skin biopsies were also placed in tissue culture medium supplemented with human serum, interleukin-2 (IL-2), and irradiated autologous blood lymphocytes. T lymphocytes grew from both plaques and univolved skin biopsies and consisted of a heterogeneous population of T-cell subsets. The immunophenotypic analysis of cultured cells was comparable to the histologic examination on frozen section, i.e., there was a greater number of CD4/CDw29+ cells than CD8+/CD45+ cells. Cultures were tested in the primed lymphocyte test (PLT) and cell-mediated lympholysis (CML) assays. All cultures tested demonstrated secondary proliferative but not cytolytic reactivity. The PLT results indicate that the cell cultures generated are autoreactive. This autoreactivity was found to be directed against non-human leukocyte antigens (HLA), i.e., minor HLA with some restriction to major HLA antigens.

Antigenic specificity of rheumatoid synovial fluid lymphocytes

The majority of rheumatoid arthritis (RA) synovial fluid lymphocytes (SFL) demonstrate markers that are suggestive of prior activation. While the mechanism(s) responsible is unknown, prior studies have suggested that certain Mycobacterium tuberculosis (MT) antigens may preferentially activate SFL in vitro. We therefore examined the ability of RA SFL to respond to purified protein derivative and an acetone-precipitable MT antigenic complex (AP-MT) and compared this with the responses by peripheral blood lymphocytes (PBL). The responses were contrasted with those elicited with tetanus toxoid (TT) and mitogenic anti-CD3. In patients with RA, the SF proliferative responses to both TT and anti-CD3 were reduced compared with responses by PB. In contrast, the SF response to purified protein derivative was maintained, and that to AP-MT was significantly increased, compared with PB. SF responses to AP-MT antigens were significantly greater than those to TT. The AP-MT activation of T lymphocytes from RA SF was characterized by an earlier peak proliferative response than that noted with matched PB. AP-MT responsiveness was not restricted to HLA-DR4 positive patients. These observations suggest that an epitope(s) contained within the MT complex of antigens, and enriched in the AP-MT complex, may be important in maintaining the chronic inflammation in at least some patients with RA.

Positive selection of Tac- (CD25) positive cells following T-cell activation. Use of immunomagnetic separation and implications for T-cell cloning

We have investigated if positive selection for cells expressing activation antigens, which appear on the cell surface during T-lymphocyte activation, could be used for cloning purposes. For this purpose, we used paramagnetic, monodisperse Dynabeads coated with anti-Tac monoclonal antibody, which recognizes CD25 (interleukin-2 receptor light chain). After the first 6-12 h of a primary response, depletion of Tac+ cells could largely abrogate the specific response. This indicated that the specifically responding cells were found among the Tac+ population. T-cell cloning was thus performed on Tac+ blasts positively selected after 18 h of a primary response, at day 6 of a primary response or during secondary stimulation, and gave a high percentage of specific clones. This method is thus a good alternative to established techniques.

Analysis of human peripheral blood T lymphocytes proliferating in response to sensitizing antigens: effect of interleukin-2 (IL-2)-responsive bystander cells

The contribution of interleukin-2 (IL-2)-responsive bystander cells to the proliferative responses of human peripheral blood T lymphocytes to antigens used for sensitization such as Purified Protein Derivative (PPD), Tetanus toxoid (T T) and Influenza virus was investigated. Marked proliferation of the unfractionated peripheral blood mononuclear cells (PBMC) was observed following stimulation with these antigens to which the individuals were known to have been sensitized previously. Depletion of large granular lymphocytes (LGL) from PBMC resulted in substantial reduction in the response of the lymphoid cells in proliferating to the antigens. Proliferation of the T4+T8- (helper)-enriched population, or T4+T8- subset depleted of any IL-2 receptor (IL-2R)-bearing lymphoid cells to these antigens was comparable to that of LGL-depleted PBMC cultures. Cell titration experiments of the blast cells generated from these cultures revealed that PBMC-derived population contained fewer antigen-reactive lymphocytes. These results, therefore, suggested that IL-2-responsive LGL through expansion affected the concentration of antigen-proliferating T cells in the antigen-stimulated PBMC cultures.

B cell growth factor (BCGF) secreting human T cell clones reactive to a soluble glycoprotein antigen, streptococcal antigen (SA)

A panel of human T cell clones bearing exclusively the helper (T4) phenotype and showing reactivities to a soluble glycoprotein antigen (185,000 dalton Mol. Wt. Streptococcal antigen, SA) is described. Two of these clones namely, SA 1.53 and SA 1.82, are found to co-produce B cell growth factor (BCGF) and interferon-gamma (IFN-gamma) in the absence of interleukin 2 (IL2) upon stimulation with phytohaemagglutinin (PHA) or the specific antigen in the presence of irradiated autologous antigen-presenting cells (APC). Secretion of the lymphokines is genetically restricted in part by DR molecules that are expressed on the cloned cells and APC. Produced BCGF is differentiated from the BCGF-promoting property of IFN-gamma in that only IFN-gamma activity, but not BCGF activity is removed and inhibited by anti-IFN-gamma antibodies. Exogenous IL2 induces secretion of BCGF and IFN-gamma of the cloned cells, an observation which involves interaction of IL2 with IL2 receptors. An analysis of the proliferative responses to antigen of the T cell clones shows that BCGF-producing clones, unlike those that secrete IL2, fail to proliferate significantly to specific antigen restimulation.

Certain human Gp120-HIV antibodies react with anti-CD4 antibodies

HIV+ human sera contain antibodies against most HIV proteins, including the envelope glycoprotein Gp120. Some of these antibodies may have an epitope that sterically resembles the CD4 region to which the Gp120 molecule binds. Amongst 58 HIV+ sera tested, we found three with the capacity to block the binding of anti-CD4 monoclonal antibodies to CD4+ cells. The serum with the highest blocking capacity was selected for further analysis. The inhibitor was shown to be an antibody that binds to the Gp120 molecule as well as to the anti-CD4 monoclonal T4.2. These CD4-mimicking antibodies were shown not to interfere with CD4-dependent reactions in vitro. Virus neutralizing experiments in vitro could not show any neutralizing effect with these antibodies alone. The HIV+ individual providing this antibody is still healthy, although HIV+ since 1983.

In vivo activated lymphoid cells (IVALC) affect the cloning efficiency of human T lymphocytes reactive to a soluble antigen, purified protein derivative

Peripheral blood mononuclear cells (PBMC) of normal individuals were found to contain a proportion (4-9%) of in vivo activated lymphoid cells (IVALC). These IVALC were characterized by their expression of interleukin 2 (IL-2) receptors, and by the ability to proliferate in the presence of exogenous IL-2. There was a good correlation between the proportion of IVALC in different cell populations and the level of cell proliferation to IL-2. It was found that IVALC isolated from autologous PBMC of Bacillus Calmette-Guerin (BCG)-immunized individuals contained no significant proportion of purified protein derivative (PPD)-reactive lymphocytes. The addition of IVALC markedly enhanced proliferative responses of the autologous T4+T8-IL-2 receptor-negative cell cultures to antigen stimulation. An increased proportion of activated (IL-2 receptor-positive) lymphocytes was generated in PBMC as compared to autologous T4+T8-IL-2 receptor negative cell cultures after stimulation with PPD. Limiting dilution analysis showed that IL-2 responsive IVALC through expansion markedly affected the cloning efficiency of antigen-proliferating T cells of autologous PPD-stimulated PBMC cultures. Only 1 out of every 11-25 blast cells generated in the PBMC cultures could establish itself as a growing colony based on determinations in six BCG-positive individuals. By using a T4+T8- population depleted of IVALC to generate PPD-reactive lymphocytes, a three- to four-fold increase in the cloning efficiency of antigen-specific cells was obtained.

Presentation of soluble antigen to human T cells by products of multiple HLA-linked loci: analysis of antigen presentation by a panel of cloned, autologous, HLA-mutant Epstein-Barr virus-transformed lymphoblastoid cell lines

Epstein-Barr virus-transformed human B lymphoblastoid cell lines (EBV-LCL) can present soluble antigens to antigen-primed T lymphocytes. In this study, we used HLA antigen-loss mutants of an EBV-LCL line (LCL 721) to demonstrate that the presentation of a soluble antigen from Candida albicans (CAN) by EBV-LCL to primed T cells can be restricted by multiple HLA determinants. Haplotype-deletion mutants that contained only the maternal or only the paternal HLA-haplotype were used to demonstrate the preferential role of autologous HLA antigens in presenting soluble antigens to Candida-primed T cells from the donor of LCL-721, and to T cells from her mother and father. Immunoselected mutants of LCL-721 showing a variety of distinct phenotypes that are deficient in HLA-DR, DQ, or DP antigen expression were tested as antigen-presenting cells. The antigen-presenting ability of these class II deficient EBV-LCL variants weakened with progressive loss of class II HLA determinants expressed on the cell surface. Our study, therefore, provides evidence for multiple HLA restriction determinants, including HLA-DR, DQ, and DP. Furthermore, LCL lacking all HLA-DR, DQ, and DP expression because of homozygous deletion of these MHC class II genes still presented CAN and Tetanus toxid (TET), although to a much lesser degree than presented by LCL-721. This suggests that determinants other than DR, DQ, and DP which are expressed on these EBV-LCL may also function as restriction elements for the proliferative T-cell response to soluble antigens.

Specific binding of antigen onto human T lymphocytes

Human T lymphocytes sensitized to Candida albicans (CA) were shown to proliferate in cultures induced with mannan, a ramified polysaccharide extracted from the cell well of CA. We presently describe that, when we used strongly labeled [3H]mannan, antigen-specific T blast cells were able to bind the labeled mannan on their membrane. The observations that irrelevant blast cells did not bind [3H]mannan, and that mannan-specific blast cells did not bind tritiated pneumococcal polysaccharide SIII, indicate the specificity of mannan binding. Mannan binding was reversible and saturable. Mannan binding on T blast cells was inhibited by preincubation with monoclonal antibodies to T3 but not to other T cell-related molecules. The characteristics of this receptor suggest its identity with the T cell receptor for antigen. The direct binding of mannan could be either due to a cross-linking of the receptor by multivalent mannan or to a recognition of mannan in association with HLA-DQ molecules, as suggested by partial blocking of mannan binding using anti-HLA-DQ monoclonal antibodies.

Presentation of Candida albicans and purified protein derivative soluble antigens by Epstein-Barr virus-transformed human lymphoblastoid B-cell lines

Cells other than the macrophage can function as antigen-presenting cells (APCs). These class II-bearing accessory cells include dendritic cells, epidermal Langerhans cells, B cells, murine B-cell tumors, and human Epstein-Barr virus-transformed lymphoblastoid cell lines (EBV-LCL). We investigated the ability of EBV-LCL to present two soluble antigens, Candida albicans and purified protein derivative of tuberculin (PPD). The EBV-LCL derived from B cells of two different individuals can present both antigens to bulk cultures of autologous antigen-primed peripheral blood lymphocytes. The responses of PPD-reactive T-cell clones were weaker to PPD when presented by EBV-LCL than by PBL-APCs, with some clones responding only to PPD presented by PBL-APCs. This suggests that EBV-LCL are not equivalent to PBL monocytes in APC function, and that expression of class II major histocompatibility complex antigen is not sufficient in enabling antigen-presenting capability.

Cell mediated PPD specific cytotoxicity against human monocyte targets: II. IL-2 expansion improves the strength and discriminatory power of CTLs used for cellular typing

Large batches of Cytotoxic T Lymphocytes (CTLs) specific for antigenic components of Purified Protein Derivative of tuberculin (PPD) were generated from 20 donors. Peripheral Blood Mononuclear cells (PBM) were stimulated with PPD, expanded with Interleukin-2 (IL-2) and finally aliquotted and cryopreserved. It was found that CTLs could be cryopreserved without loss of activity, and compared to generating CTLs in primary culture alone, IL-2 expanded CTLs were stronger and discriminated better. To study their HLA restriction specificity, the CTLs were tested against a panel of 50 target cell donors using PPD pulsed monocytes as antigen presenting target cells. Reproducibility was examined by analysis of variance. Guided by the results, the mean value of 2 tests was selected as the basis for qualitative assignments.

HLA-DR3 and -DR4 control T-lymphocyte responses to mumps and Coxsackie B4 virus: studies on patients with type 1 (insulin-dependent) diabetes and healthy subjects

To study the relationships between the responses to viral antigens and the HLA-DR3 and -DR4 associations in Type 1 (insulin-dependent) diabetes mellitus, the frequency of T-lymphocyte proliferating in response to mumps, Coxsackie B4 and varicella-zoster antigens was determined. A decreased frequency was found in T lymphocytes able to respond to mumps or Coxsackie B4 when presented together with DR3, as compared with the frequency of T lymphocytes able to respond to these viruses together with other DR determinants. This was not found for varicella-zoster or purified protein derivative of tuberculin. In contrast, an increased frequency was found in T lymphocytes responding to mumps or Coxsackie B4 together with DR4, compared with other DR determinants. The results were similar in Type 1 diabetic and healthy individuals. The results suggest that elements on the DR3 and DR4 molecules may control T-lymphocyte responses to mumps and Coxsackie B4 viruses.

The proliferative immune response to autologous Epstein-Barr virus-transformed lymphoblastoid cells. I. Studies with HLA haplotype loss variants demonstrate a role for MHC-linked genes

The human Epstein-Barr virus transformed lymphoblastoid cell line (EBV-LCL) 721 and MHC haplotype loss variants derived from it were utilized to dissect the functional role of MHC genes in the proliferative response of autologous T lymphocytes to EBV-LCL. LCL-721 is heterozygous at all phenotypically defined MHC loci. One type of LCL-721 variant expresses only determinants encoded by the maternal (m) haplotype and the other expresses determinants encoded by the paternal (p) haplotype. Autologous (individual A) primary proliferative responses are strong to each type of haplotype deletant. The strong tertiary responses to the priming haplotype in comparison to the relatively weak responses to the reciprocal haplotype indicate that MHC linked genes encoded by each haplotype are important in the autologous response to EBV-LCL. Similar specific tertiary responses are observed when peripheral blood lymphocytes (PBLs) from the donor's mother are used as responding cells. Allogeneic responses were also studied by priming PBLs from unrelated donors with the haplotype deletants. Quantitative comparisons of the proliferation by primed allogeneic and autologous lymphocytes stimulated by irradiated PBLs from donor A and her mother, and by LCL-721 and its variants, show that some of the tertiary responses involve specific recognition of EBV-LCL while others detect recognition of alloantigens.

HLA class II restriction repertoire of antigen-specific T cells. I. The main restriction determinants for antigen presentation are associated with HLA-D/DR and not with DP and DQ

In order to study the HLA class II restriction repertoire in antigen presentation to T cells, T lymphoblasts (T-LB) of ten different HLA class II donors were generated by a simple and rapid technique; peripheral blood lymphocytes (PBL) were restimulated in vitro with purified protein derivative (PPD) or tetanus toxoid (TET), and then propagated in interleukin-2 containing conditioned medium (IL2-CM). These T-LB appeared to be antigen specific and devoid of alloreactivity. Antigen was presented to these T-LB by allogeneic irradiated PBL as antigen-presenting cells (APC) in 179 combinations. T-LB proliferative responses were restricted mainly by determinants associated with HLA-DR and not with -DP or -DQ; in 102 fully DR mismatched T-LB/APC combinations matching for DP or DQ determinants had no significant influence on T-LB responses. For PPD, preferential DR1 restriction was observed, and the results suggest a preferential DRw11 vs. DRw12 restriction for TET. Moreover, DRw13 may be associated with low anti-PPD T-LB responsiveness.

RISH III. Haplotype-sharing in immune responses

A number of hypotheses have been proposed for the reactivity of lymphocytes with allogeneic tissue. However, these hypotheses have not been generally accepted for they cannot accommodate the observation that lymphocytes from chimeras cooperate with each other. Also, only a few percent of lymphocytes react with allogeneic tissue in rejection reactions.

Phenotyping of proliferating cells in cultures of human lymphocytes

Lymphocytes stimulated with mitogens, alloantigens or soluble antigens were pulsed with tritiated thymidine to label proliferating cells. Aliquots of the cells were labeled with OKT 4 or OKT 8 mouse monoclonal antibodies and then incubated in microtiter wells coated with goat anti-mouse immunoglobulin G (IgG). Unattached cells were flushed out of the wells: individual wells were then separated for counting in scintillation fluid in a B counter. This method permits simple characterization of the relative T cell subset proliferative responses and is clinically applicable.

HLA-class II restriction of the proliferative T lymphocyte responses to nickel, cobalt and chromium compounds

Peripheral blood mononuclear cells from nickel and/or cobalt or chromium sensitive patients were stimulated with the appropriate metal compound for 7 days in culture. The transformed blasts were separated from non-transformed small cells on Percoll density gradients. The blasts, maintained in interleukin-2 containing medium and enriched for T cells, were both antigen specific and devoid of alloreactivity. The metal compound primed T cell blasts from all patients showed a good proliferative response on restimulation with the priming compound in the presence of autologous adherent cells (AC). Analysis of HLA class II phenotypes of allogeneic AC that could serve as antigen presenting cells indicated that responsiveness of T cell blasts from most but not all patients could be explained on the basis of HLA-DR as a restricting element. We conclude that products of other class II loci (HLA-DQ and/or HLA-DP) might also serve as restricting elements for a secondary in vitro proliferative response to these metal compounds.

Characterization of Chlamydia trachomatis serotypes by human T-lymphocyte clones

T cells primed to Chlamydia trachomatis serotypes A, F, and K were cloned by limiting dilution. All T-lymphocyte clones obtained reacted only with C. trachomatis antigens. The proliferative capacity of 89 clones was studied with autologous non-T cells as antigen-presenting cells and the chlamydia serotypes A, B, D, F, K, and LGV-2 as antigens. Most of the clones reacted to several of the chlamydia strains, indicating common antigenic determinants. Other T-cell clones reacted with only a few serotypes. On the basis of the proliferation of the T-cell clones to the chlamydia strains and to interleukin-2, different reactivity patterns were obtained, which possibly can be used to differentiate among the chlamydia strains.

Antigen-specific T cell clones restricted by DR, DRw53 (MT), or DP (SB) Class II HLA molecules. Inhibition studies with monoclonal HLA-specific antibodies

T lymphocyte clones (TLCs) specific for Chlamydia trachomatis were obtained after limiting dilution of activated T cells from a single donor, BS (HLA-A3; B7,15; DR1, 4; DRw53; DPw4). Most of the proliferative TLCs obtained apparently used restriction elements on DR1 or DR4 molecules, expressed in the antigen-presenting cells (APC). The restriction pattern of two TLCs, however, closely followed the DRw53 specificity, while one TLC seemed to be restricted by elements on DPw4 molecules. A panel of murine monoclonal antibodies (Mabs) was employed to further dissect the restriction specificities. The proliferative capacity of some of the TLCs was studied with and without Mabs directed against different HLA molecules, using non-T cells, monocytes, and peripheral blood dendritic cells as APC. Two Mabs, 7.2 and D-54, which seem to detect monomorphic determinants on HLA-DR, inhibited both DR- and DRw53-restricted TLCs. One Mab, 109d6 which reacts with DRw53 determinants, selectively inhibited the DRw53-restricted TLCs. The DP-restricted TLC was not inhibited significantly by any tested Mabs, including two Mabs with putative specificity for monomorphic determinants on the DP molecule.

Detection of HLA restricted anti-minor histocompatibility antigen(s) reactive cells from skin GVHD lesions

Recipients of marrow grafts from HLA-identical, (including MLC non-reactive) sibling donors have a 40-50% incidence of acute graft vs. host disease (GVHD); the involvement of non-HLA linked, minor histocompatibility antigens (miHA) has been implicated. One of the target tissues of GVHD is the skin where morphological analysis of biopsy specimens is often used to support this diagnosis. We have obtained skin biopsy specimens from the site of GVHD lesions, grown the cells in the presence of T cell growth factor (TCGF) and feeder cells, and tested these cultured cells in the primed lymphocyte test (PLT) and cell mediated lympholysis (CML) assay. Five of six cell cultures tested demonstrated secondary proliferative but not cytolytic reactivity; cells from one culture demonstrated both reactivities. The cell culture populations generated are presumably directed against non-HLA antigens, i.e., miHA whose expression is restricted by an HLA antigen of the recipient. The data are consistent with the suggestion that in the majority of these cultures, the restriction element may be a determinant encoded within the HLA-D region: DQ, DR, and possibly DP based on panel testing. Although the number of cases is small, these preliminary data demonstrate the feasibility of this type of culturing system and also suggest that the cellular immunological events leading to the manifestation of skin GVHD lesions may be predominantly a delayed type hypersensitivity reaction.

Major histocompatibility complex restriction of tetanus toxoid-specific human T lymphocyte clones

Peripheral blood mononuclear cells (PBMC) from an HLA DRw6/7 individual were stimulated with tetanus toxoid (TT). T cell blasts were cloned by the limiting dilution technique in the presence of TT and irradiated autologous PBMC (iPBMC). Twelve were propagated under interleukin 2 and restimulated weekly with TT and iPBMC. All proliferated specifically in response to TT or either the alpha or beta chain of the toxin molecule. HLA restriction of specific proliferative responses was analyzed using a panel of HLA-typed unrelated donors and selected families, and blocking experiments with anti-HLA class I and class II monoclonal antibodies (mAb). Three types of restriction were observed: (a) autologous restriction; the inhibition observed using anti-HLA DR mAb as well as family studies performed previously with a similarly restricted clone obtained from the same donor suggest an HLA DRw6-linked restriction; (b) an HLA DR7 restriction was found for 2 clones, specific for alpha or beta chain; the identical pattern of inhibition obtained with two different mAb belonging to the same cluster suggests that these clones may be restricted by the same (or a very close) epitope of the HLA DR7 molecule; (c) an unusual restriction pattern was found for one clone; PBMC from more than 80% of donors could present TT whatever their degree of HLA compatibility with the autologous donor. Family studies were unable to disclose any restriction with known class II (or class I) antigens. While no inhibition was observed with anti-DR or -DC reagents, a mAb that recognizes class I antigen when associated with beta 2-microglobulin did inhibit the proliferation of this clone.

The mechanism of antigen presentation by endothelial cells

Endothelial cells line the vessels and lymphatics forming a barrier between circulating T cells and the extravascular tissue site of antigen. We have suggested that circulating T cells recognize antigen on the surface of endothelial cells, resulting in the activation of the endothelium such that the endothelial cells then release the key mediators of a cell-mediated immune response. To test this hypothesis, we have evaluated the extent to which endothelial cells can signal antigen-specific T cell activation. We have shown that cultured endothelial cells are as effective as macrophages in lymphocyte activation and that this activation is HLA-DR restricted. In additional experiments we have established that endothelial cells synthesize both Ia and IL-1 early in the signaling process. To eliminate any possible contribution of other cell types participating in the T cell-endothelial cell interaction, we have shown that cloned endothelial cells present antigen to cloned T cells. Moreover, there appeared to be a preference of selected T-cell populations for different types of antigen presenting cells. These experiments document that endothelial cells are independently competent antigen presenting cells.

Role of HLA class II products in proliferative T-lymphocyte responses to PPD. Evidence of a regulatory influence associated with MB1

HLA class II determinants were analysed for their role in monocyte-T-cell interactions in the proliferative response to purified protein derivative (PPD). Allogeneic cell combinations of monocytes and T cells were tested with a range of suboptimal PPD concentrations. For each cell combination tested, a summary measure to characterize the antigen-induced response curve was calculated by means of regression analysis of the response to the dose of PPD added, thus obviating a further need to correct for mixed lymphocyte reactivity. In 200 distinct monocyte-T-cell combinations, HLA-DR appeared to be the major restricting element. Additionally, a marginal influence of HLA-MB or -MT matching was observed and no evidence of HLA-SB-restricted responses. Remarkably, the HLA-MB1 specificity was significantly associated with low responsiveness in DR sharing monocyte-T-cell combinations, indicating a modulating role of MB1 in DR-restricted T-cell responses.

Dissociation among Ia antigen expression, accessory cell function, and antigen processing in two acute monoblastic leukemia lines

To better understand the role of Ia antigen expression, accessory cell function, and antigen ingestion in antigen presentation and the initiation of T cell proliferation, we studied these events in two acute monoblastic leukemia (AMoL) lines. The cell lines were positive for surface Ia antigen; one stimulated proliferation of the allogeneic mononuclear cells in mixed lymphocyte culture and culture supernatants from the other line contained interleukin 1 (IL-1) when tested for comitogen activity in a standard mouse thymocyte assay. The AMoL cells also contributed accessory factors for mitogen-induced proliferative responses by T cells. High numbers of cells of one of the lines tended to suppress mitogen induced T cell proliferation. Irradiated trinitrophenylated AMoL cells were able to stimulate TNP-specific HLA-DR matched T cell blasts to proliferate. However, when irradiated AMoL cells were cultured with a protein antigen (tetanus toxoid or varicella zoster) plus antigen-specific parental T cell blasts, antigen presentation failed to occur. Diminished phagocytosis by the AMoL cells, together with reduced catabolism of labelled antigen, is a likely explanation for this finding. Our results demonstrate that the concurrent presence of a complex protein antigen and Ia-positive monocytic leukemia cells capable of accessory function is alone insufficient to maintain antigen-specific T cell proliferation. Moreover, these findings suggest that antigen processing, involving ingestion and reexpression of antigenic determinants, is an essential aspect of antigen presentation not tightly linked to Ia antigen expression or IL-1 production in these AMoL lines.

Development and characterization of interleukin-2-independent antigen-specific human T cell clones that produce multiple lymphokines

The development of antigen-specific T lymphocyte lines and clones has greatly facilitated the investigation of T-cell recognition of and response to foreign antigens. In the present study, human antigen-specific helper T cell lines and clones which are completely independent of exogenous interleukin-2 (IL-2) have been developed by cyclic restimulation with the soluble antigen keyhole limpet hemocyanin (KLH) to which the T cell donor had previously been immunized. These T cells uniformly bear the OKT4 phenotype and were shown to require both histocompatible antigen-presenting cells (APC) and antigen for optimal proliferation. The T cell line was composed of a highly antigen-specific and clonable T cell population. Following four cycles of antigen stimulation, limiting dilution cloning analysis showed a Poisson distribution of clonable T cells with a precursor frequency of 0.62, and from 88 to 92% of viable clones were specific for the stimulating antigen. Individual clones were obtained which recognized KLH with either DR 1 (one parental Ia haplotype of the donor) or DR 2 (the other parental Ia haplotype) allogeneic APC, but not both. Following stimulation with KLH, the T cell clones produced IL-2. Peak amounts of IL-2 were assayable in the first 6 to 24 hr after stimulation. In contrast, virtually no IL-2 was detectable in supernatants at 72 to 96 hr, suggesting autoutilization by the proliferating T cells. In addition, some clones were also capable of producing both B cell growth factor and IL-2 following KLH stimulation. These IL-2-independent T cells appeared to be derived from a discrete Leu 8-negative subclass of T4+ cells and expressed the full complement of Ia antigen of the donor. Thus, soluble antigen-specific human helper T cell clones have been produced which can be maintained in the absence of exogenous IL-2, elaborate their own growth factors and other immunoregulatory lymphokines, and show fine DR-related restriction to either one or the other parental DR haplotypes in antigen-stimulated proliferative responses.

Immunodeficiency with defective T-cell response to interleukin 1

Normal proliferation of T cells in vitro requires production of and response to the lymphokine interleukin 2 (IL-2). Optimal IL-2 production by T cells is dependent on the monokine interleukin 1 (IL-1). A 10-year-old male with recurrent infections and failure to thrive was evaluated for possible defects in the production and response to IL-1 and IL-2. The patient had normal levels of serum immunoglobulins and a normal distribution of circulating T-cell subsets. However, the in vitro proliferative response of his peripheral blood mononuclear cells (PBMC) to phytohemagglutinin was depressed (40% of normal) and the response of his PBMC to antigens was absent. Delayed hypersensitivity skin tests and in vitro response to tetanus toxoid remained absent despite repeated immunizations. Monocyte function in this patient was normal as judged by the following criteria: normal expression of Ia antigens (77% +), normal IL-1 production, and normal capacity to present tetanus toxoid to a maternal T-cell line specific for tetanus toxoid antigen. The abnormal phytohemagglutinin response of the patient's PBMC was corrected by the addition of exogenous IL-2. IL-2 production by the patient's phytohemagglutin-stimulated PBMC was severely deficient but was corrected by the addition of phorbol 12-myristate 13-acetate, suggesting a defective response to IL-1. T-cell blasts derived from a normal subject but not T-cell blasts derived from the patient absorbed out IL-1 activity from a preparation of purified human IL-1. These results indicate that the patient's T-cell deficiency was due to a defective T-cell response to IL-1 and suggest that IL-1 plays an important role in the in vivo immune response.

Lack of cell-mediated cytotoxicity towards Chlamydia trachomatis infected target cells in humans

Induction of cell-mediated cytotoxicity towards Chlamydia trachomatis infected target cells was studied in humans. PHA-derived lymphoblasts, infected with inactivated or virulent LGV-2 chlamydial particles, were used as target cells. Chlamydial primed T cell blasts or specific, cloned T cells were used as effector cells. A highly sensitive 18 hours lytic assay employing 111In-labelled target cells was used. Specific cytotoxicity towards C. trachomatis infected target cells in humans could not be detected. This was the case regardless of the origin of the effector cells or the various protocols tested. However, this assay was capable of yielding significant positive results with effector cells primed to alloantigens. We conclude that cell-mediated cytotoxicity towards bacterial infected target cells probably does not play a major role.

Parasite antigen-specific human T cell lines and clones. Major histocompatibility complex restriction and B cell helper function

The development of T lymphocyte lines and clones of defined specificity has become an important method for investigating both T cell recognition of foreign antigens as well as T cell influence on B cells. In the present study, human antigen-specific T cell lines and clones have been derived from a patient with a naturally acquired filarial infection. These T cells are of the helper phenotype (Leu 1+, Leu 2-, Leu 3+) and are independent of exogenous interleukin-2. Furthermore, these T cells have been shown to require both antigen-presenting cells and antigen for optimal proliferation. Helper function mediated by these T cells as manifested by the in vitro induction of parasite-specific antibody was antigen-dose dependent, requiring much lower antigen concentrations than those necessary to induce blastogenesis. More importantly, there is an absolute requirement of the T cell line for HLA-DR histocompatible antigen-presenting cells; clones derived from this T cell line show a more specific DR-related restriction--to only one of the two parental DR haplotypes in antigen stimulated proliferative responses. Such parasite antigen specific human helper T cell lines and clones should prove useful in exploring the fine control of the host response to naturally acquired helminth infections. In addition, these long-term T cell lines and clones can provide a potent tool for examining not only the events involved in human T cell responses to parasite antigens, but also into the associated cellular and humoral factors necessary for the B cell responses which follow.

Antigen-specific HLA-restricted human T-cell lines. I. An MT3-like restriction determinant distinct from HLA-DR

The results presented provide evidence that the HLA specificity known as MT3, BR4, or Hon7 can serve as a restriction epitope for the proliferation of certain T cells responding to mumps viral antigen. This restriction determinant was found to be HLA-linked in family studies, and to segregate centromeric to a crossover between HLA-B and DR in one family. In the population studied, the specificity was found to be associated with the DR antigens DR4, DR7, and DRw9, which are known to be associated with MT3. The ability of accessory cells to present mumps antigen in the context of this supertypic restriction determinant was blocked by a monoclonal antibody specific for MT3. Since MT3 (BR4, Hon7) has been shown to be expressed on molecules distinct from DR, our experiments suggest that such molecules are functionally important in antigen presentation to T cells.

Antigen-specific proliferative human T-lymphocyte clones with specificity for Chlamydia trachomatis

Blast-enriched suspensions of T cells primed for Chlamydia trachomatis antigen were cloned by a limiting dilution technique. A cloning efficiency of 20-25% was obtained. T-lymphocyte clones (TLC) with high proliferative responses were selected for further studies. Kinetic studies showed a peak response between 60 and 84 h after antigen stimulation. The TLC were OKT4+. They were specific for the chlamydial antigen and did not respond to other antigens when non-T cells were used as antigen-presenting cells (APC). Antigen-specific proliferation of the TLC required that the responding TLC and the APC shared class-II HLA determinants--that is, HLA-D/DR molecules. The true clonal nature of the TLC was confirmed by subcloning experiments.

Class-II HLA restriction of antigen-specific human T-lymphocyte clones. Evidence of restriction elements on both DR and MT molecules

Blast-enriched suspensions of T cells primed for Chlamydia trachomatis antigen were cloned by a limiting dilution technique. The class-II HLA restriction of T-lymphocyte clones (TLC) was studied by using allogeneic antigen-presenting cells (APC) carrying foreign class-II HLA antigens. Most of the TLC were restricted by one or the other of the D/DR determinants of the T-cell donor; that is, they did not respond when antigen was presented by APC expressing foreign D/DR determinants. Furthermore, heterogeneity of the DR4-expressing molecule could be demonstrated by T-cell clones from one person; APC from family members expressing DR4 gave high proliferative responses, whereas no proliferation was observed with most APC from unrelated persons expressing DR4. This heterogeneity of DR4 was confirmed by mixed lymphocyte culture (MLC) experiments, indicating a close relationship between restriction epitopes and those that activate allogeneic T cells. Other clones seemed to be restricted by other class-II HLA determinants, most probably MT determinants of the T-cell donor. The restriction specificities were confirmed by subcloning experiments.

Cell mediated lympholysis; a modified technique using 111indium-oxine-labelled targets

The isotope 51Cr generally used in the cell mediated lympholysis (CML) assay suffers from the disadvantage of low specific activity, poor incorporation and high spontaneous release, limiting the CML assay to 4-6 h. We have labelled PHA derived human lymphoblasts with the isotope 111indium (using 111indium-oxine) and evaluated these cells as targets in CML. The level of 111In-oxine incorporation decreased rapidly in the presence of serum; in the absence of serum approximately 85% of the available isotope in the supernatant was incorporated into the blasts. Under the labelling conditions used, spontaneous release was 1.6-2%/h on average allowing an effector phase of 18 h. About 5-8% of the released isotope was reutilized by the effector cells during an 18 h incubation period. Extending the CML assay from 6 to 18 h greatly increased the cytotoxicity. At an effector to target ratio of 25:1, the average per cent specific release increased from 15 to 50%. The use of 111In-oxine labelled targets in the CML therefore increases the sensitivity of the test and allows fewer effector and target cells to be used as compared with 51Cr techniques.

IL-2 secretion by soluble antigen-reactive human T-cell clones

Human tetanus toxoid specific T-cell lines and clones capable of producing IL-2 were established. IL-2 production occurred only when the antigen-specific T cells were cultured with both tetanus toxoid antigen and an autologous, irradiated adherent cell population. The T-cell lines and clones remained strictly dependent on exogenous IL-2 for proliferation at all other times. Phenotypic characterization with monoclonal antibodies recognizing T-cell subsets revealed that the antigen-specific lines and clones bore predominantly OKT3 and OKT4 markers with essentially no OKT8 positive cells present. T-cell clones which were demonstrated to secrete IL-2 activity could also partially deplete media of IL-2 if cultured in the absence of soluble antigen and irradiated adherent cells.

Unusual restriction of a proliferative line reacting with influenza A and B viruses

A human T-cell line, B3, has been obtained by cloning spleen cells at limiting dilutions in the presence of influenza-A-virus-infected autologous cells. B3 cells were OKT 3+4+8-, E rosetting+, Sig- and were HLA-DR (+) after stimulation and HLA-DR (-) when resting. They proliferate specifically in the presence of influenza-virus-infected cells. Remarkable is that (a) the proliferation was obtained with viruses of both A and B types and (b) only autologous cells seem to be able to present the viral antigen to B3 cells.

HLA-D/DR restriction of Langerhans cell-dependent antigen activation of T lymphocytes. The same D/DR determinants are restriction elements on monocytes and Langerhans cells

In previous studies we have shown that the response of T cells to antigen presented by epidermal Langerhans cells (LC) is restricted by products of the HLA-D region. An optimal antigen-specific response required that the LC used for antigen presentation shared both, or at least one, of the D/DR determinants of the T-cell donor. These studies were, however, disturbed by a strong allogeneic response induced by the foreign D/DR determinants of the LC. We report here that by separating the antigen-specific T cells from those that are alloreactive, a clearer picture of the D/DR restriction phenomenon may be obtained. Furthermore, the present studies demonstrate that the same D/DR determinants function as restriction elements on peripheral blood monocytes and LC.

Both DR and MT class II HLA molecules may restrict proliferative T-lymphocyte responses to antigen

Antigen-primed T-cell blasts may be separated from alloreactive T cells on Percoll gradients. By means of this method, HLA restriction of antigen-specific proliferative T-cell responses may be studied, using allogeneic antigen-presenting cells carrying foreign D/DR antigens. The reported data confirm that the D/DR molecules as such are major restriction elements in the T-cell response to herpes simplex virus (HSV) and purified protein derivative (PPD). However, evidence is presented that other Class II HLA molecules, the MT molecules, may also function as restriction elements for the HSV response.

The role of HLA-DR antigens in PPD-stimulated lymphocyte-monocyte interactions

Autologous monocytes are required for an optimal lymphocyte proliferative response to purified protein derivate of tuberculin (PPD) in vitro and for a mixed lymphocyte culture induced by alloantigens. In the proliferative response to PPD we found that autologous monocytes could be replaced with HLA-DR-compatible monocytes and partly with HLA-DR semi-identical. In spite of a statistically significant difference between autologous and HLA-DR disparate monocytes in their cooperative capacity with PPD-stimulated lymphocytes, replacement in nearly one third of the cases was possible. These findings were supported by more detailed studies in which increasing numbers of allogenic and autologous monocytes were added to the isolated lymphocytes in the presence of PPD. It is concluded that the serologically defined HLA-DR antigens alone give insufficient information of the restriction elements controlling the PPD-stimulated lymphocyte-monocyte interactions.

HLA-D/DR restriction of proliferative T cell responses to antigen. Enrichment of antigen-specific T cell blasts and evidence of preferential HLA-D/DR restriction

Antigen-specific T cell blasts may be separated from alloreactive cells on Percoll gradients. The absence of alloreactivity allowed us to study HLA-D/DR restriction of proliferative T cell responses towards PPD and HSV antigens using allogeneic antigen-presenting cells. An overriding impact of self HLA-D/DR determinants as restriction elements for in vivo sensitized T cells was demonstrated. Furthermore, evidence was obtained that the proliferative PPD response might be preferentially restricted by HLA-D/DR 1.

An influenza virus matrix protein-specific human T cell line with helper activity for in vitro anti-hemagglutinin antibody production

A human helper T cell line (F14m) activated by the matrix protein purified from A/X31 influenza virus has been developed. After activation by antigen for 7 days, and reculture with matrix protein and irradiated autologous feeder cells, the cells obtained from an in vivo influenza virus-immunized donor have been growing in the presence of interleukin 2 for more than 7 months. The cells all belong to the helper-inducer T cell subset and most of them express surface membrane HLA-DR antigens. A small number (approximately 10(3)) of F14m T cells provided optimal help for 1 X 10(5) autologous T-depleted lymphocytes for production of anti-A/X31 but not anti-B/HK antibodies. The F14m T cells produce soluble factors (S14m) able to help B cells to secrete anti-A/X31 antibodies. F14m and S14m were shown to help antibody production to hemagglutinin when cultured with B cells and the whole virus. The specificity of the T cell line for type-A matrix protein was confirmed by the ability of S14m to provide help for anti-A/JAP (A/H2/N2) but not for anti-B/HK antibody production. These data provide evidence for matrix protein-specific T helper cells and factors able to provide help for antibody production against hemagglutinin, a distinct protein of the same virus.

Antigen-specific human T-lymphocyte clones. Genetic restriction of influenza virus-specific responses to HLA-D region genes

Human T lymphocytes, primed in vitro to influenza virus, were cloned by limiting dilution and expanded using medium containing interleukin 2 and feeder cells. A detailed analysis of the genetic requirements for induction of T-cell proliferation was conducted using a panel of cells from unrelated donors and two families who had previously been extensively phenotyped for HLA region antigens. Clones obtained from a Dw1, Dw3 individual required Dw1,DR1 histocompatibility for successful presentation of viral antigens by antigen-presenting cells. The antigen-presenting ability segregated with HLA-B,D,DR in an informative HLA-A/B recombinant individual. In contrast, some TLCs responded to antigen presented by cells that did not share known HLA antigens, and in one informative family, reactivity did not segregate with HLA. None of the T-cell clones reacted to allogeneic cells in the absence of antigen, suggesting that the TLCs do not bear receptors that recognize both influenza virus and alloantigen. In antibody-blocking studies, Dw1, DR1-restricted clones were blocked by all monoclonal anti-DR framework antibodies. The non-HLA-restricted TLCs were blocked by some, but not all, of the anti-DR framework monoclonal antibodies. These results confirm and extend the role of HLA-D region gene products in antigen presentation and also provide evidence that yet undefined cell interaction products, which may include hybrid structure, are able to participate in antigen-specific proliferative responses by human T cells.

Studies on the role of HLA-DR in macrophage-T cell interactions

The purpose of this paper is to illustrate the difficulties we have encountered in attempting to analyse the role of HLA-DR in the antigen-dependent co-operation between macrophages and T cells which leads to a T-cell proliferative response. We have adopted the two most commonly used approaches; attempted inhibition by anti-HLA-DR antisera and study of co-operation between cells of unrelated individuals, and have found both methods unsatisfactory. With the first method we found that anti-HLA antisera could inhibit proliferative responses in a non-specific manner. Both anti-HLA-A, B and anti-HLA-DR antisera could inhibit and this inhibition was largely Fc-dependent. Using pepsin-digested antisera we have no evidence for a unique role for HLA-DR in these proliferative responses. The second method, study of co-operation between cells of unrelated individuals, proved extremely difficult to analyse because of the background allogeneic reaction. Whether cells of two individuals appeared to co-operate to give an antigen-specific response depended on the number of cells used and the calculations applied to the data. However, it was clearly possible to demonstrate co-operation between DR different individuals.