HLA-DR Determinants Research Articles

In-vitro inhibition of IFNγ+ iTreg mediated by monoclonal antibodies against cell surface determinants essential for iTreg function

BackgroundIFNγ-producing CD4+CD25+Foxp3+ PBL represent a subtype of iTreg that are associated with good long-term graft outcome in renal transplant recipients and suppress alloresponses in-vitro. To study the mechanism of immunosuppression, we attempted to block cell surface receptors and thereby inhibited the function of this iTreg subset in-vitro using monoclonal antibodies and recombinant proteins.MethodsPBL of healthy control individuals were stimulated polyclonally in-vitro in the presence of monoclonal antibodies or recombinant proteins against/of CD178, CD152, CD279, CD28, CD95, and HLA-DR. Induction of IFNγ+ iTreg and proliferation of effector cells was determined using four-color fluorescence flow cytometry. Blockade of iTreg function was analyzed using polyclonally stimulated co-cultures with separated CD4+CD25+CD127-IFNγ+ PBL.ResultsHigh monoclonal antibody concentrations inhibited the induction of CD4+CD25+Foxp3+IFNγ+ PBL (anti-CD152, anti-CD279, anti-CD95: p < 0.05) and CD4+CD25+CD127-IFNγ+ PBL (anti-CD178, anti-CD152, anti-CD279, anti-CD95: p < 0.05). Effector cell proliferation increased with increasing antibody concentrations in culture medium (anti-CD178 and anti-CD279: p < 0.05). Conversely, high concentrations of recombinant proteins induced formation of CD4+CD25+Foxp3+IFNγ+ PBL (rCD152 and rCD95: p < 0.05) and decreased cell proliferation dose-dependently (rCD178 and rCD95: p < 0.05). Our data suggest an inverse association of iTreg induction with effector cell proliferation in cell culture which is dependent on the concentration of monoclonal antibodies against iTreg surface determinants. 3-day co-cultures of polyclonally stimulated PBL with separated CD4+CD25+CD127-IFNγ+ PBL showed lower cell proliferation than co-cultures with CD4+CD25+CD127-IFNγ- PBL (p < 0.05). Cell proliferation increased strongly in CD4+CD25+CD127-IFNγ- PBL-containing co-cultures in the presence of monoclonal antibody (anti-CD28, anti-CD152, anti-CD279: p < 0.05) but remained low in co-cultures with CD4+CD25+CD127-IFNγ+ PBL (with the exception anti-CD28 monoclonal antibody: p < 0.05). Monoclonal antibodies prevent iTreg induction in co-cultures with CD4+CD25+CD127-IFNγ- PBL but do not efficiently block suppressive iTreg function in co-cultures with CD4+CD25+CD127-IFNγ+ PBL.ConclusionsCD178, CD152, CD279, CD28, CD95, and HLA-DR determinants are important for induction and suppressive function of IFNγ+ iTreg.

A conformationally-biased, response-selective agonist of C5a acts as a molecular adjuvant by modulating antigen processing and presentation activities of human dendritic cells

A partial mechanism by which a conformationally-biased, response-selective agonist of complement component C5a, Tyr-Ser-Phe-Lys-Pro-Met-Pro-Leu-D-Ala-Arg or YSFKPMPLaR (EP54), acts as a molecular adjuvant is presented by showing the manner in which this peptide engages human dendritic cells (DC). Confocal microscopy was used to show that fluorescent-labeled EP54 (0.2 microM) and fluorescent-labeled B and T cell epitopes attached to EP54 (i.e., EP54-containing vaccines, 0.2 microM) were internalized by human DCs well within 30 min of exposure. After 24 h of exposure, EP54 and the B and T cell epitopes of the EP54-containing vaccines (20 microM) were presented on the DC surface in the context of HLA-ABC and HLA-DR determinants. Also, exposure of DCs to EP54 (50 microg/ml) induced the activation of genes specific for the Th1 cytokines IL-6, IL-12, INFgamma, and TNFalpha as well as the Th2 cytokine IL-4. Internalization, HLA expression, and cytokine gene activation were not observed in the presence of the inactive, scrambled EP54 constructs arguing that these effects of EP54 are mediated predominately via C5a receptors on the DC surface.

Characterization of anti-islet cytotoxic human T-cell clones from patients with type 1 diabetes mellitus

To identify important anti-islet T-cells and their target antigen(s), we have isolated and characterized seventeen human T-cell clones which are reactive to an extract of rat insulinoma (RIN) cells from three children with new onset type 1 diabetes mellitus (T1D). Of these 17 clones, 15 were found tissue specific. Six of eight tested tissue specific clones did not recognize known islet antigens such as GAD, 52 kDa islet protein, insulin, ICA512, and heat shock protein 60 (hsp60), suggesting that these clones recognize an autoantigen not previously identified. All tested clones were phenotypically CD4 and functionally Th0 or Th0/Th1 cells. One RIN extract reactive clone (2E9) recognized hsp60 and was CD4 and TCR α/β positive. This clone also proliferated in response to human and rat islets suggesting that the antigen is conserved between species. This clone and 75% of all the tested RIN reactive clones exhibited anti-islet cytotoxicity by lysing target cells coated with RIN extract. HLA DR determinants may play a role in this cytotoxic activity since preincubation with HLA DR antibody decreased the anti-islet cytoxicity of the two tested clones. In conclusion, we have isolated RIN reactive CD4+T-cell clones from diabetic subjects, six of which appears tissue specific and non-reactive to putative important islet antigens, and in turn may be recognizing yet undiscovered islet antigens. The high frequency anti-islet cytotoxic properties of the islet reactive clones provides evidence for a role of CD4+ cytotoxic T-lymphocytes in the diabetic process. Further, the isolation of hsp60 reactive clone with anti-islet cytotoxic properties suggests that cell mediated immunity against hsp60 may be important in the pathogenesis of diabetes.

Strong HLA-DR expression in microsatellite stable carcinomas of the large bowel is associated with good prognosis.

Progression of colorectal cancer may follow either of two main genetic routes: the chromosome- or microsatellite-instability pathways. Association between the patients' prognosis and microsatellite instability has been questioned. Improved survival has previously been found in patients with expression of HLA-DR antigens on their tumour cells. In this study, the expression of HLA-DR antigen was investigated by immunohistochemistry in 357 large bowel carcinomas stratified by microsatellite instability status. Sixteen per cent of the tumours showed strong HLA-DR expression and 35% had weak DR expression. We confirmed that patients with strong positive HLA-DR staining had improved survival (P<0.001) compared to patients with no HLA-DR expression. Strong epithelial HLA-DR staining was significantly associated with high level of microsatellite instability (P<0.001). In the subgroup of tumours with characteristics typical of the chromosomal instability phenotype, i.e. in microsatellite-stable tumours, the patients positive for the HLA-DR determinants showed better survival than those without HLA-DR expression. The protective effect of HLA-DR expression on survival was confirmed by multivariate analysis, both in the whole patient group and in the microsatellite-stable/microsatellite instability-low group. This might be explained by enhanced T-cell mediated anti-tumour immune responses against tumour cells in the HLA-DR positive tumours. The finding of better patient survival in the subgroup of strong HLA-DR positive microsatellite-stable tumours may have clinical implications for these patients.British Journal of Cancer (2002) 87, 756–762. doi:10.1038/sj.bjc.6600507 www.bjcancer.com© 2002 Cancer Research UK

T-cell receptor bias in patients with allergic bronchopulmonary aspergillosis

CD4+ Th2 helper cell mediated immune responses have been shown to play a crucial role in the pathogenesis of ABPA. HLA and TCR are the candidate genes, which can influence the specificity of these responses. We have previously established a strong association of HLA DR2/5 in ABPA susceptibility. The study was designed to determine whether allergen specific T cell express a limited usage of T cell receptor (TCR) Vβ gene repertoire in ABPA and to find an association of susceptible HLA-DR determinants with the identified TCR gene segments. TCR Vβ typing was performed on antigen specific T cell lines from 14 ABPA and 12 nonABPA patients. The majority of ABPA patients (86%) expressed allergen specific T cells with Vβ13 genes indicating its role in susceptibility, whereas in nonABPA controls, Vβ1 genes T cell repertoires were predominantly expressed. The unrestricted pattern of Vβ gene amplification seen before antigen stimulation suggests an oligoclonal expansion of a specific T cell population in response to the allergen Asp f 1 in ABPA and nonABPA patients. The increased usage of Vβ13 in ABPA and Vβ1 in nonABPA indicates their importance in susceptibility and resistance, respectively.

Exogenous topical lactoferrin inhibits allergen-induced Langerhans cell migration and cutaneous inflammation in humans.

Lactoferrin (LF), an iron-binding protein found in exocrine secretions, is known to possess antibacterial properties. It has recently been proposed that LF may also influence inflammatory reactions. To characterize in humans the ability of recombinant homologous LF to inhibit the induced migration of epidermal Langerhans cells (LCs) from the skin, a process known to be dependent upon the proinflammatory cytokines tumour necrosis factor (TNF)-alpha and interleukin 1beta and to influence cutaneous inflammatory reactions. We investigated the anti-inflammatory properties of LF in human volunteers. Topical exposure to LF 2 h prior to sensitization caused a significant reduction in contact allergen (diphenylcyclopropenone, DPC)-induced LC migration from the epidermis as judged by the altered frequency of cells expressing either HLA-DR or CD1a determinants. That this reduction was secondary to an inhibition of TNF-alpha production was indicated by the fact that LF failed to influence LC migration induced by intradermal injection of this cytokine. In approximately 50% of those volunteers who displayed local inflammation in response to DPC, LF was found to cause a discernible reduction in the clinical severity of the reaction, associated with reduced infiltration of inflammatory cells. These data demonstrate that LF is able to influence cutaneous immune and inflammatory responses, possibly because of an impaired production of local proinflammatory cytokines.

Sterically stabilized liposomes bearing anti-HLA-DR antibodies for targeting the primary cellular reservoirs of HIV-1

The ability of liposomes bearing anti-HLA-DR Fab′ fragments at the end termini of polyethyleneglycol chains (sterically stabilized immunoliposomes) to target HLA-DR expressing cells and increase the accumulation of liposomes into lymphoid organs has been evaluated and compared to that of conventional liposomes, sterically stabilized liposomes and conventional immunoliposomes after a single subcutaneous injection to mice. The accumulation of sterically stabilized liposomes in lymph nodes was higher than that of conventional liposomes. Sterically stabilized immunoliposomes accumulated much better than conventional immunoliposomes in all tissues indicating that the presence of PEG has an important effect on the uptake of immunoliposomes by the lymphatic system. Fluorescence microscopy studies showed that sterically stabilized liposomes are mainly localized in macrophage-rich areas such as the subcapsular region of lymph nodes and in the red pulp and marginal zone of the spleen. In contrast, sterically stabilized immunoliposomes mostly accumulated in the cortex in which follicles are located and in the white pulp of the spleen. As the human HLA-DR determinant of the major histocompatibility complex class II is expressed on activated CD4+ T lymphocytes and antigen presenting cells such as monocyte/macrophages and dendritic cells, known as the cellular reservoirs of HIV-1, liposomes bearing anti-HLA-DR antibodies constitute an attractive approach to concentrate drugs in HIV-1 reservoirs and improve their therapeutic effect.

Targeting lymph nodes with liposomes bearing anti-HLA-DR Fab′ fragments

The ability of liposomes bearing anti-HLA-DR Fab′ fragments to target cells expressing the human HLA-DR determinant of the major histocompatibility complex class II (MHC-II) has been evaluated and compared to that of conventional liposomes. Anti-HLA-DR immunoliposomes did not bind to HLA-DR-negative cells. In contrast, a high level of binding was observed following incubation of immunoliposomes with cells bearing important levels of human HLA-DR. The accumulation of conventional and murine anti-HLA-DR immunoliposomes in different tissues has been investigated following a single subcutaneous injection given in the upper back of C3H mice. Anti-HLA-DR immunoliposomes resulted in a much better accumulation in the cervical and brachial lymph nodes when compared to conventional liposomes. The accumulation in the liver was similar for both liposomal preparations, whereas an approximately twofold decrease in accumulation was observed for immunoliposomes in the spleen. Given that HLA-DR surface marker is expressed on monocyte/macrophages and activated CD4+ T lymphocytes, the primary cellular reservoirs of the human immunodeficiency virus (HIV), the use of liposomes bearing surface-attached anti-HLA-DR could constitute a convenient strategy to more efficiently treat this debilitating retroviral disease. Moreover, the reported incorporation of high amounts of host-encoded HLA-DR proteins by HIV particles renders the use of liposomes bearing anti-HLA-DR antibodies even more attractive.

The presence of host-derived HLA-DR1 on human immunodeficiency virus type 1 increases viral infectivity.

Human immunodeficiency virus type 1 (HIV-1) incorporates several host cell components when budding out of the infected cell. One of the most abundant host-derived molecules acquired by HIV-1 is the HLA-DR determinant of the major histocompatibility complex class II (MHC-II) molecules. The fact that CD4 is the natural ligand of MHC-II prompted us to determine if such virally embedded cellular components can affect the biology of the virus. Herein, we report for the first time that the incorporation of cellular HLA-DR1 within HIV-1 enhances its infectivity. This observation was made possible with virions bearing or not bearing on their surfaces host-derived HLA-DR1 glycoproteins. Such virus stocks were prepared by a transient-expression system based on transfection of 293T cells with a recombinant luciferase-encoding HIV-1 molecular clone along with plasmids encoding the alpha and beta chains of HLA-DR1. Cell-free virions recovered from transfected cells were shown to have efficiently incorporated host-derived HLA-DR1 glycoproteins. Infectivity was increased by a factor of 1.6 to 2.3 for virions bearing on their surfaces host-derived HLA-DR1. The observed enhancement of HIV-1 infectivity was independent of the virus stocks used and was seen in several T-lymphoid cell lines, in a premonocytoid cell line, and in primary peripheral blood mononuclear cells. Finally, we determined that the presence of virion-bound cellular HLA-DR1 is associated with faster kinetics of virus infection. Taken together, these results suggest that HLA-DR-1-bearing HIV-1 particles had a greater infectivity per picogram of viral p24 protein than HLA-DR1-free virions.

Mapping of dominant HLA-DR determinants recognized via the indirect pathway

Mapping of dominant HLA-DR determinants recognized via the indirect pathway

The MHC class‐II and CD44 molecules are involved in the induction of tumour necrosis factor (TNF) gene expression by human monocytes stimulated with tumour cells

Tumour necrosis factor alpha (TNF) mRNA is detected in the macrophage infiltrate surrounding the tumour, but the cellular/molecular interactions leading to TNF gene expression in macrophages are unknown. The in vitro system in which human blood monocytes are stimulated with human cancer cells for TNF release was used to study such interactions. Monoclonal antibodies (MAbs) against various adhesion molecules (LFA-1, LFA-3, ICAM-1, VNR, VLA beta I chain) were unable to block TNF production in co-culture of monocytes with a human pancreatic carcinoma (HPC) cell line. However, anti-CD44 and anti-HLA-DR MAbs effectively blocked TNF release and TNF-mRNA induction in monocytes. Pre-incubation of monocytes with anti-HLA-DR and tumour cells with anti-CD44 MAbs had a similar effect. It was concluded that CD44 molecules are involved in tumour-monocyte interactions and that HLA-DR determinants of monocytes are engaged in signal transduction for TNF gene activation. These findings may suggest that certain surface determinants of tumour cells act as ligands for MHC class-II molecules and induce TNF production in monocytes.

Human astrocytes are only partially competent antigen presenting cells. Possible implications for lesion development in multiple sclerosis.

Highly purified astrocyte cultures from human embryonic brain were examined for their capacity to present antigen to human leukocyte antigen (HLA) class II compatible, cytolytic CD4+ T lymphocytes. Most astrocytes constitutively expressed HLA class I products and LFA-3 (CD58). Constitutive expression of HLA class II, LFA-1 alpha (CD11a) and ICAM-1 (CD54) was lower and varied among different cultures, while LFA-2 (CD2) was absent. IFN-gamma alone or in combination with TNF-alpha strongly enhanced expression of HLA class I, HLA-DR, -DP, -DQ, LFA-1 alpha and ICAM-1, but did not affect expression of LFA-2 (CD2) and LFA-3 (CD58). TNF-alpha alone induced only HLA class I and ICAM-1, but not HLA class II or LFA-1 alpha. Cytokine treated, but not untreated astrocytes were able to present protein (auto-)antigens to specific T lymphocyte lines. Astrocytes expressing appropriate major histocompatibility complex class II products were lysed by CD4+ T cells specific for myelin basic protein or tetanus toxoid. The lytic response was antigen dose dependent and HLA-DR restricted. It could be blocked by antibodies against HLA-DR determinants and against the adhesion molecules LFA-1 alpha and ICAM-1. In remarkable contrast to their susceptibility to T cell lysis, antigen presenting astrocytes were not only completely unable to induce T cell proliferation but even inhibited proliferation. The results indicate that, although human astrocytes have the potential to present protein antigens to CD4+ T cells, they do not induce the co-stimulatory factors required to trigger the complete T cell activation programme.

MHC class II antigen expression by ocular cells in proliferative diabetic retinopathy.

An immunohistological study was performed on ciliary biopsies of the pars plana obtained surgically in 10 patients suffering from diabetic retinopathy and on 15 surgical specimens of pre-retinal neovascularized membranes. Using immunofluorescence and immunoperoxidase procedures, linear deposits of IgG, IgA and complement components were found in the 8 pars plana from patients with proliferative diabetic retinopathy, at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from normal pars plana and from the cases of background retinopathy. Moreover, pigment and non-pigment epithelial cells were found to express HLA DR and DQ determinants, in six of the eight patients with proliferative retinopathy. Immunohistological examination of pre-retinal membranes showed deposition of immunoglobulins and complement components within the connective stroma and along the new blood vessels. Endothelial cells of the newly formed vascular walls strongly expressed class II antigens on their membrane, as well as scattered stromal cells. As neither pigment epithelial cells nor retinal vascular endothelial cells normally express class II determinants, our results suggest the involvement of immunological phenomena in intraocular proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction plays a role in the initiation or extension of intra-ocular proliferation remains to be determined.

Selection of T cell receptor V beta elements by HLA-DR determinants predisposing to rheumatoid arthritis.

Rheumatoid arthritis (RA) is genetically linked to a sequence motif encoding for the middle portion of the alpha-helical loop, which is adjacent to the antigen-binding groove of the HLA-DR molecule. The disease-associated element might be involved in binding the antigen or in interacting with the T cell receptor (TCR). To investigate the contribution of the disease-associated element in T cell recognition events, we studied structural requirements in the interaction of T cell clones with HLA-DR determinants. T cell clones restricted to disease-associated HLA-DR determinants were established by allogeneic stimulation of HLA-DRB1*0401+ or *0401- responders with HLA-DRB1*0404/8+ stimulators. Allele specific primer sets were used to identify the V beta gene segment expressed by individual clones. Sequence analysis was applied to study the diversity of the TCR beta-chain junctional regions. The repertoire of TCR V beta elements was strongly biased toward the usage of V beta 6. HLA-DRB1*0401+ and *0401- donors preferentially recruited V beta 6+ T cells to recognize the disease-associated HLA-DR determinant. Sequence data revealed that the V beta 6.6/7 and V beta 6.8/9 subtypes of the V beta 6 multigene family were overrepresented. The TCR beta chains were characterized by a high degree of junctional diversity, supporting the view that a multitude of peptide-DR complexes were recognized and that the preferential use of V beta 6 was dictated by the TCR beta chain-DR beta 1 chain contact. T cells reactive with the disease-associated HLA-DR structure are nonrandomly selected. The HLA-DR component predisposing to RA might define molecular requirements that restrict the TCR-HLA interaction. Thus, the phenomenon of HLA association in RA might reflect a genetic control of T cell recognition, through the selection of the TCR repertoire.

Vaccinia virus-specific human CD4+ cytotoxic T-lymphocyte clones.

Vaccinia virus-specific cytotoxic T-lymphocyte (CTL) clones were established from a healthy donor, who had been immunized with vaccinia virus vaccine, by stimulation of peripheral blood lymphocytes with UV-inactivated vaccinia virus antigen. The phenotype of all of the clones established was CD3+ CD4+ CD8- Leu11-. We used a panel of allogenic vaccinia virus-infected B-lymphoblastoid cell lines and demonstrated that some of the clones recognized vaccinia virus epitopes presented by human leukocyte antigen (HLA) class II molecules. Monoclonal antibodies specific for either HLA-DP or HLA-DR determinant reduced the cytotoxicity of specific clones. The HLA-restricted cytotoxicity of the clones is vaccinia virus specific, because vaccinia virus-infected but not influenza virus-infected autologous target cells were lysed. Using vaccinia virus deletion mutants, we found that some of the CTL clones recognize an epitope(s) that lies within the HindIII KF regions of the vaccinia virus genome. These results indicate that heterogeneous CD4+ CTL clones specific for vaccinia virus are induced in response to infection and may be important in recovery from and protection against poxvirus infections.

HLA-DR expression in macaque neuroendothelial cells in vitro and during SIV encephalitis

HLA-DR expression in neuroendothelial cells (NEC) was studied during the course of SIV encephalitis in rhesus monkeys. HLA-DR determinants were detected on NEC in monkeys with SIV encephalitis, but not in control animals. In situ hybridization with an SIV probe indicated that HLA-DR expression was not a consequence of SIV replication within NEC. Cultured rhesus NEC stimulated with gamma interferon expressed HLA-DR to a higher degree than cultured brain fibroblasts or astrocytes. These data support the contention that NEC participate in retrovirus-induced inflammation and autoimmunity within the central nervous system.

Are soluble monocyte-derived HLA class II molecules candidates for immunosuppressive activity?

Supernatants of human blood monocyte cultures suppressed PHA responses (IL-2 synthesis, IL-2R expression, DNA synthesis) of autologous and allogeneic lymphocytes. The main suppressive activity was found in the 65-kDa (and 23-kDa) range. It could be incompletely neutralized by mAb specific for a non-polymorphic HLA DR determinant and could also be adsorbed to and eluted from an anti-DR immunoabsorbent column. On blots of monocyte lysates and monocyte culture supernatants, the mAb RoDR recognized antigens of nearly the same M r. The hypothesis that soluble HLA DR αβ heterodimers or β chains are likely candidates for the suppressor factor was confirmed by analogous effects of purified HLA DR molecules. We favor a model in which soluble MHC class II molecules (in contrast to surface-bound ones) may interfere with the association and cross-linking processes necessary for T cell activation by competing for CD4 binding sites.

Immunohistologic Study of Proliferative Vitreoretinopathy

An immunohistologic study was performed on pars plana specimens obtained by biopsy in ten patients with rhegmatogenous retinal detachment, with or without proliferative vitreoretinopathy. Using immunofluorescence or immunoperoxidase procedures, linear deposits of IgG, IgA, and complement components were found in the eight cases of retinal detachment with proliferative vitreoretinopathy at the basal pole of the pigment epithelial cells and within the stroma. In contrast, these deposits were absent from the normal pars plana and from the retinal detachment without proliferative vitreoretinopathy. Moreover, pigment and nonpigment epithelial cells were found to express HLA-DR and HLA-DQ determinants in six of the eight patients with proliferative vitreoretinopathy. Our results are similar to those obtained in a previous study on proliferative diabetic retinopathy, which suggests the involvement of autoimmune phenomena in proliferative diseases and eventual interactions between the immune system and peptide growth factors. However, whether or not this immune reaction functions in the initiation or extension of intraocular proliferative syndromes remains to be determined.

Modified MHC restriction of donor-origin T cells in humans with severe combined immunodeficiency transplanted with haploidentical bone marrow stem cells.

The choice of class II MHC determinants that serve as self-recognition elements for murine CD4+ T cells is thought to be determined by the environment in which T cells mature rather than their genotype. Patients with severe combined immunodeficiency (SCID) reconstituted with T cell depleted haploidentical parental stem cells provide an excellent model for studying this phenomenon in humans. After engraftment, the T cells that develop in these infants are all of donor origin. We sought to determine whether the successful immune reconstitution observed in two such SCID chimeras involved modification of the MHC restriction of Ag recognition by the genetically donor T cells as they matured to become competent T cells in the infants' microenvironment. A tetanus toxoid (TT)-specific T cell line and TT-specific T cell clones were established from the blood of two reconstituted SCID patients and from their maternal donors. T cell responsiveness was determined by [3H]thymidine incorporation after TT presentation by EBV-transformed B cell lines (EBV-B) from various donors. The TT-specific T cell line from patient 1 proliferated when presented Ag by patient, maternal donor, and paternal APC. A CD4+ donor origin clone that proliferated when presented TT by patient and paternal EBV-B, but not by maternal donor EBV-B, was isolated from each patient. TT recognition by these clones was shown to be restricted by the HLA DR determinant shared by patient and father, but not present in the donor. Four TT-specific clones isolated from maternal donors failed to proliferate when presented TT by the appropriate paternal EBV-B. These studies demonstrate that, in these human SCID bone marrow chimeras, engrafted donor-origin stem cells maturing to competent T cells in the recipient microenvironment are capable of utilizing recipient HLA determinants as restriction elements for Ag recognition. This suggests that human, as well as murine, MHC restriction patterns for Ag recognition by CD4+ T cells are environmentally determined.

Immunologic Aspects of Mycobacterial Infections

Immunosuppressive mechanisms loom as important factors in depression of delayed-type hypersensitivity responses during active tuberculosis. Nonspecific suppression may be mediated by circulating immune complexes containing mycobacterial polysaccharides such as D-arabino-D-galactan. The mechanism of suppression involves activation of monocyte production of immunosuppressive prostaglandin E2. Peripheral blood mononuclear cells from patients with tuberculosis include increased numbers of monocytes that suppress the response to tuberculin purified protein derivative (PPD). Antigen-specific suppression is associated with monocyte activation by a number of criteria, including decreased surface expression of HLA-DR determinants and increased production of interleukin 1 (IL-1). The increased production of IL-1 is associated with--and may have a causal relation to--immunosuppression. A second parallel regulatory mechanism involves PPD-specific suppression by Fc gamma receptor-bearing lymphocytes. The consequence of these immunosuppressive circuits is depression of tuberculin-induced blastogenesis, production of IL-2, and generation of IL-2 receptors. These findings suggest that natural infection with Mycobacterium tuberculosis may result in immunosuppression. Studies of potentially protective antigens in experimental systems must be designed to assess and avoid activation of suppressor circuits.