Quantitative analysis of cell surface HLA structures by means of monoclonal antibodies

Association between blood transfusion after kidney transplantation and risk for the development of de novo HLA donor-specific antibodies and poor clinical outcomes: A single-center retrospective study

BACKGROUND

Blood transfusion after kidney transplantation may increase the risk of sensitization and development of de novo human leukocyte antigen (HLA) donor-specific antibodies (DSAs). This study aimed to evaluate whether blood transfusion during the first year after kidney transplantation influences the development of de novo DSAs and clinical outcomes of kidney transplantation recipients.

METHODS

This retrospective cohort study included nonsensitized first-time kidney transplantation recipients at Tianjin First Central Hospital from 2010 to 2022. The incidence of de novo DSA development and clinical outcomes between the groups were compared. Luminex single antigen beads were used to monitor DSAs.

RESULTS

Of the 538 non-HLA-sensitized kidney transplantation recipients included in the study, 164 patients who received at least one unit of leukoreduced red blood cell transfusion within the first year (the transfused group), whereas the remaining 374 patients received no blood transfusion (the non-transfused group). Our analysis showed that there was a significant difference in the development of de novo DSAs and de novo anti-class I HLA-Ab between the two groups. Indeed, the transfused recipients had a higher serum creatinine and lower estimated glomerular filtration rate (eGFR) at 1-, 6-, and 12-month (all p > 0.05) after transplantation. Futhermore, a higher incidence of CMV infection, antibody-mediated rejection (AMR), hyper acute rejection (HAR), and delayed graft function (DGF) was identified in the transfused group (all p < 0.05). The graft survival was lower in the transfused group compared with patients in the non-transfused group (P = 0.002). Blood transfusion post-transplantation was a risk factor for de novo DSAs development but not an independent predictive factor for AMR and graft loss (odds ratio = 2.064 [1.243-3.429], p = 0.005).

CONCLUSIONS

Our study showed that blood transfusion after transplantation is associated with the occurrence of de novo DSAs increasing an immunological risk for poor clinical outcomes for kidney transplantation recipients.

Effect of blood transfusion post kidney transplantation on de novo human leukocytes antigen donor-specific antibody development and clinical outcomes in kidney transplant recipients: A systematic review and meta-analysis

The relationship between blood transfusion following kidney transplantation (KT) and the development of de novo donor-specific antibodies (dnDSA) is controversial. This was investigated by conducting a meta-analysis of studies on patients who underwent KT with or without blood transfusion, and by evaluating the effect of post-KT blood transfusion on clinical outcomes of kidney transplant recipients. Relevant studies in the PubMed, EMBASE, and Cochrane Library databases were identified from inception to July 1, 2022. Two reviewers independently extracted data from the selected articles and estimated study quality. A fixed effects or random effects model was used to pool data according to the heterogeneity among studies. Data included in the meta-analysis were derived from 11 studies with a total of 19,543 patients including 6191 with and 13,352 without blood transfusion post-KT. We assessed the pooled associations between blood transfusion and occurrence of dnDSA and clinical outcomes of transplant recipients. Blood transfusion was strongly correlated with the development of dnDSA (relative risk [RR] = 1.40, 95% confidence interval [CI]: 1.17-1.67; P < 0.05). Patients with blood transfusion had a higher risk of developing anti-human leukocyte antigen (HLA) class I dnDSA than non-transfused patients (RR = 1.75, 95% CI: 1.14-2.69; P < 0.05) as well as significantly higher rates of antibody-mediated rejection (AMR) (RR = 1.41, 95% CI: 1.21-2.35; P < 0.05) and graft loss (RR = 1.75, 95% CI: 1.30-2.35; P < 0.05). There were no statistically significant differences between the two groups in the development of anti-HLA antibodies, anti-HLA class II dnDSA, and anti-HLA class I and II dnDSA; delayed graft function; T cell-mediated rejection; acute rejection; borderline rejection; or patient death. Our results suggest that blood transfusion was associated with dnDSA development in KT recipients. The findings of this systematic review also suggest that post-KT blood transfusion recipients have a higher risk of AMR, and graft loss compared with non-transfused patients. Evidence from this meta-analysis indicates that the use of blood transfusion post-KT is associated with a significantly higher risk of immunological sensitization. More and higher quality results from large randomized controlled trials are still needed to inform clinical practice.

Post-Transplantation Early Blood Transfusion and Kidney Allograft Outcomes: A Single-Center Observational Study

The association between blood transfusion and the occurrence of de novo HLA donor specific antibodies (DSA) after kidney transplantation remains controversial. In this single-center observational study, we examined the association between early blood transfusion, i.e. before 1-month post-transplantation, and the risk of DSA occurrence, using Luminex based-methods. In total, 1,424 patients with a minimum of 1-month follow-up were evaluated between January 2007 and December 2018. During a median time of follow-up of 4.52 years, we observed 258 recipients who had at least one blood transfusion during the first month post-transplantation. At baseline, recipients in the transfused group were significant older, more sensitized against HLA class I and class II antibodies and had a higher 1-month serum creatinine. Cox proportional hazards regression analyses did not show any significant association between blood transfusion and the risk of de novo DSA occurrence (1.35 [0.86–2.11], p = 0.19), the risk of rejection (HR = 1.33 [0.94–1.89], p = 0.11), or the risk of graft loss (HR = 1.04 [0.73–1.50], p = 0.82). These data suggest then that blood transfusion may not be limited when required in the early phase of transplantation, and may not impact long-term outcomes.

Human Leucocyte Antigen Sensitisation and Its Impact on Transfusion Practice

Human leucocyte antigen (HLA) sensitisation, including the formation of antibodies against HLA, can cause serious effects in patients receiving blood. Under certain circumstances, donor HLA antibodies in the blood product can trigger the patient's granulocytes to release mediators that cause transfusion-associated lung injury (TRALI), a serious complication of transfusion. The HLA systems of both donor and patient are involved in transfusion-associated graft-versus-host disease, which is a rare disease with a high mortality. Patient HLA antibodies can destroy incompatible platelets and may cause refractoriness to platelet transfusion. Identification of a patient's HLA antibody specificities is necessary for issuing compatible platelets to overcome refractoriness. Many techniques for the detection and identification of HLA antibodies have been developed, including complement-dependent cytotoxicity assay, bead-based assays, the platelet adhesion immunofluorescence test, and the monoclonal antibody-specific immobilisation of platelet antigens assay. Different strategies for the selection of HLA-compatible platelets are applied. These strategies depend on the breadth of antibody reactivity and range from avoiding single HLA antigens in the platelet concentrates issued to apheresis of platelets from HLA-identical donors. The mechanisms of HLA sensitisation and the efforts made to provide compatible blood products to sensitised patients are reviewed in this article from the perspective of clinical transfusion medicine.

Rapid quantification of the latent reservoir for HIV-1 using a viral outgrowth assay

HIV-1 persists in infected individuals in a stable pool of resting CD4⁺ T cells as a latent but replication-competent provirus. This latent reservoir is the major barrier to the eradication of HIV-1. Clinical trials are currently underway investigating the effects of latency-disrupting compounds on the persistence of the latent reservoir in infected individuals. To accurately assess the effects of such compounds, accurate assays to measure the frequency of latently infected cells are essential. The development of a simpler assay for the latent reservoir has been identified as a major AIDS research priority. We report here the development and validation of a rapid viral outgrowth assay that quantifies the frequency of cells that can release replication-competent virus following cellular activation. This new assay utilizes bead and column-based purification of resting CD4⁺ T cells from the peripheral blood of HIV-1 infected patients rather than cell sorting to obtain comparable resting CD4⁺ T cell purity. This new assay also utilizes the MOLT-4/CCR5 cell line for viral expansion, producing statistically comparable measurements of the frequency of latent HIV-1 infection. Finally, this new assay employs a novel quantitative RT-PCR specific for polyadenylated HIV-1 RNA for virus detection, which we demonstrate is a more sensitive and cost-effective method to detect HIV-1 replication than expensive commercial ELISA detection methods. The reductions in both labor and cost make this assay suitable for quantifying the frequency of latently infected cells in clinical trials of HIV-1 eradication strategies.

The eradication of HIV-1 from infected individuals is stymied by the persistence of the virus in a stable reservoir of latently infected CD4⁺ T cells. Latently infected cells can be found in all HIV-1 infected individuals at a very low frequency and allow the virus to persist despite antiretroviral therapy for the lifetime of an infected patient. Current efforts are focused on identifying small molecules or immune strategies to eliminate these latently infected cells. To assess the efficacy of these elimination strategies in HIV-1 infected patients, we must be able to measure the size of the latent reservoir. While an assay developed previously in our lab can measure the size of this latent reservoir, it is too laborious and costly to be utilized in large-scale HIV-1 eradication trials. We have developed a rapid assay to measure the size of the HIV-1 latent reservoir more amenable to these eradication trials.

Blood transfusions in organ transplant patients: mechanisms of sensitization and implications for prevention

Sensitization by previous pregnancies or transplants is considered unavoidable, but it is transfusions given to these patients that leads most often to broad sensitization. Both leukocytes and red cells carry a significant HLA antigen load, and residual leukocytes and/or red cell HLA may explain why leukocyte-reduced units are unable to prevent sensitization to any significant degree. Prevention of sensitization will require a more active effort to avoid blood transfusions, whenever possible. When transfusions are required, there is evidence that the use of HLA-matched blood or immunosuppression in selected situations may reduce sensitization, even in patients previously exposed to alloantigens. These additional measures are not logistically straightforward or devoid of risks and need to be confirmed by rigorous studies. However, remaining as passive observers when patients become broadly sensitized should no longer be considered an acceptable alternative for potential transplant recipients.

Targeted cell-cell interactions by DNA nanoscaffold-templated multivalent bispecific aptamers

Cell-cell interactions are essential for multicellular organisms, playing important roles in their development, function, and immunity. Herein a bottom-up strategy to construct self-assembled DNA nanostructures is reported, consisting of multivalent, bispecific, cell-targeting aptamers to specifically induce cell-cell interactions. Various DNA nanoscaffolds are rationally designed to assemble aptamers with different valencies and flexibilities, and their cellular binding capabilities are tested. Multivalent aptamers, assembled on more rigid scaffolds, display higher binding activities. Further, multivalent bispecific aptamer fusion molecules are constructed based on this configuration, and successfully link two types of cells. Using cell-targeting aptamers, the presented strategy eliminates the need to chemically modify cell surfaces and offers excellent cell specificity, binding efficiency, and stability. This proof-of-concept study establishes that multivalent bispecific aptamers linked on DNA-nanoscaffolds can mediate cellular engagement, which could lead to their use in directing or guiding cell-cell interactions in many biological events.

A specific cytotoxic T-lymphocyte epitope presentation system for antitumor immunity

The magnitude of CTL-mediated immunity response is highly dependent on the density of antigenic peptide-MHC I complexes at the cell surface. In this study, we adopt a novel strategy to promote the surface level of specific peptide-MHC I complexes. The strategy combines the inhibition of transporter associated with antigen processing (TAP) with the delivery of specific peptide into endoplasmic reticulum directly without the help of TAP. First, RNA interference (RNAi) technology was used to inhibit TAP expression for blocking endogenous epitope-assembled MHC class I on cell surface. Second, a peptide epitope of interest was covalently linked onto human beta-2-microglobulin (beta2m). Both TAP-specific siRNA and the peptide-linked beta2m were delivered into antigen-presentation cells sequentially or simultaneously using a retrovirus delivery system. The combined strategy produces a significant amount of MHC I loaded with specific epitopes on the surface while reducing endogenously peptide-assembled MHC class I both in vitro and in vivo. The efficacy of induction of specific immune response with the strategy against tumor cells is demonstrated in both tumor cell lines and a syngenic graft tumor model.

A one-step method for determining the maximum number of bound antibodies, and the affinity and association rate constants for antibody binding

OBJECTIVE

A reliable analysis of antibody binding may lead to more successful selection of the optimal antibodies. The most important parameters are affinity (equilibrium dissociation constant, Kd), the number of antigen sites on the cells (Bmax) and the on (ka) and off (kd) rate constants of binding. The affinity and the number of cellular binding sites are usually determined by equilibrium binding experiments and subsequent Scatchard analysis. The on and off rate constants are determined by kinetic binding experiments. However, it is necessary to perform two to three different types of experiment in order to determine these parameters.

METHODS

We have developed an alternative one-step method based on a kinetic binding experiment and a mathematical description of antibody binding to antigen. The method was compared with kinetic and equilibrium binding methods.

RESULTS

The results obtained using two different cell lines were in good agreement with results obtained with Scatchard analysis and kinetic binding experiments.

CONCLUSION

An alternative one-step method for determination of parameters describing binding of antibodies to antigens on cells has been developed. The method gives reliable estimates of affinity and number of antigens and in addition gives information on the kinetics of binding.

Segregation of HLA-C from ICAM-1 at NK cell immune synapses is controlled by its cell surface density

NK cell activity is controlled by the integration of signals from numerous activating and inhibitory receptors at the immunological synapse (IS). However, the importance of segregation and patterning of proteins at the NK cell IS is unknown. In this study, we report that the level of expression of HLA-C on target cells determined its supramolecular organization and segregation from ICAM-1 at the NK cell IS, as well as its capacity to inhibit NK cell cytotoxicity. At YTS NK cell synapses formed with target cells expressing low levels of HLA-C (i.e., 10(4)/cell surface), a multifocal patterning of MHC class I protein predominated, whereas for higher levels of expression (10(5)/cell surface), clusters of HLA-C were more commonly homogeneous, ring-shaped, or containing multiple exclusions. This correlation of protein density with its patterning at the IS was independent of ATP- or actin-driven processes. Importantly, ICAM-1 and HLA-C segregated only at synapses involving target cells expressing high levels of MHC protein. For peripheral blood NK clones, there were specific thresholds in the level of target cell HLA-C needed to inhibit cytotoxicity and to cause segregation of HLA-C from ICAM-1 at the synapse. Thus, the synapse organization of HLA-C, determined by its level of expression, could directly influence NK cell inhibition, e.g., by regulating the proximity of activating and inhibitory receptors. For the first time, this suggests an important function for the assembly of an inhibitory NK cell IS. More broadly, segregation of proteins at intercellular contacts could transmit information about protein expression levels between cells.

Development of humanized antibodies as cancer therapeutics

Recent success in the development of monoclonal antibody-based anti-cancer drugs has largely benefitted from the advancements made in recombinant technologies and cell culture production. These reagents, derived from the antibodies of mouse origin, while maintaining the exquisite specificity and affinity to the tumor antigens, have low immunogenicity and toxicity in human. High-level expressing cell clones are generated and used to produce large quantities of the recombinant antibodies in bioreactors in order to meet the clinical demand for therapeutic applications. In this report, the systems and general methodologies developed by us to construct and produce humanized antibodies from the parent mouse antibodies are described. Once the humanized antibodies are available, they can be applied in three principal forms for cancer therapy: (1) naked antibodies, (2) drug- or toxin conjugates, and (3) radioconjugates. Using the humanized anti-CD22 (epratuzumab) and anti-carcinoembryonic antigen (ant-CEA; labetuzumab) antibody prototypes, clinical applications of naked and radiolabeled humanized monoclonal antibodies are described.

Characterization of a new humanized anti-CD20 monoclonal antibody, IMMU-106, and Its use in combination with the humanized anti-CD22 antibody, epratuzumab, for the therapy of non-Hodgkin's lymphoma

PURPOSE

A new humanized anti-CD20 monoclonal antibody (MAb), IMMU-106, was evaluated to elucidate its action as an antilymphoma therapeutic, as a single agent, and in combination with the anti-CD22 MAb, epratuzumab.

EXPERIMENTAL DESIGN

Antiproliferative effects, apoptotic effects, and the ability of IMMU-106 to mediate complement-mediated cytotoxicity and antibody-dependent cellular cytotoxicity on a panel of non-Hodgkin's lymphoma (NHL) cell lines were compared with the chimeric anti-CD20 MAb, rituximab, and evaluated in light of the various levels of antigen expression by the cell lines. In vivo therapy studies were performed in SCID mice bearing disseminated Raji lymphoma.

RESULTS

The mechanisms of cytotoxicity of IMMU-106 were found to be similar to rituximab, and include direct apoptosis, antibody-dependent cellular cytotoxicity, and complement-mediated cytotoxicity. IMMU-106 was also found to be very similar to rituximab in terms of antigen-binding specificity, binding avidity, and dissociation constant. Treatment of Raji-bearing SCID mice with IMMU-106 yielded median survival increases of up to 4.2-fold compared with control mice. Survival in mice treated with IMMU-106 plus epratuzumab was compared with IMMU-106 treatment alone. Although the combined treatment did not improve median survival, an increased proportion of long-term survivors was observed. An enhanced antiproliferative effect was also observed in vitro in SU-DHL-6 cells when IMMU-106 was combined with epratuzumab. These findings are consistent with the up-regulation of CD22 expression observed after pretreatment of NHL cells in vitro with CD20 MAb (IMMU-106).

CONCLUSIONS

It is expected that in humans IMMU-106 should be at least as effective as rituximab and, due to its human framework construction, it may exhibit different pharmacokinetic, toxicity, and therapy profiles. In addition, it may be possible to enhance efficacy by combination therapy comprised of anti-CD20 and other B-cell lineage targeting MAbs, such as epratuzumab. The current results emphasize that in vitro as well as in vivo studies with many of the NHL cell lines were generally predictive of the known activity of anti-CD20 MAbs in NHL patients, as well as the enhanced efficacy of epratuzumab combined with rituximab observed in early clinical trials.

Characterization of scFv-Ig Constructs Generated from the Anti-CD20 mAb 1F5 Using Linker Peptides of Varying Lengths

The heavy (VH) and light (VL) chain variable regions of the murine anti-human CD20 mAb 1F5 were cloned, and four single-chain Ab (scFv) molecules were constructed using linker peptides of variable lengths to join the VH and VL domains. Three constructs were engineered using linker peptides of 15, 10, and 5 aa residues consisting of (GGGGS)3, (GGGGS)2, and (GGGGS)1 sequences, respectively, whereas the fourth was prepared by joining the VH and VL domains directly. Each construct was fused to a derivative of human IgG1 (hinge plus CH2 plus CH3) to facilitate purification using staphylococcal protein A. The aggregation and CD20 binding properties of these four 1F5 scFv-Ig derivatives produced were investigated. Both size-exclusion HPLC column analysis and Western blots of proteins subjected to nonreducing SDS-PAGE suggested that all four 1F5 scFv-Ig were monomeric with m.w. of ∼55 kDa. The CD20 binding properties of the four 1F5 scFv-Ig were studied by ELISA and flow cytometry. The 1F5 scFv-Ig with the 5-aa linker (GS1) demonstrated significantly superior binding to CD20-expressing target cells, compared with the other scFv-Ig constructs. Scatchard analysis of the radiolabeled monovalent GS1 scFv-Ig revealed a binding avidity of 1.35 × 108 M−1 compared with an avidity of 7.56 × 108 M−1 for the native bivalent 1F5 Ab. These findings suggest that the GS1 scFv-Ig with a short linker peptide of ∼5 aa is the best of the engineered constructs for future studies.

Modification of HLA expression on peripheral lymphocytes and monocytes during aging

Immunosenescence involves modifications of humoral and cellular immunity. Here we report the analysis of human leukocyte antigen (HLA) expression on T lymphocytes, B lymphocytes and monocytes of 58 healthy subjects aged 23-95 years old. Using a double staining immunofluorescence and flow cytometry analysis, we have determined the percentages of cells expressing HLA class-I and HLA-DR antigens. The number of antigenic sites expressed per cell were evaluated for HLA-ABCw, HLA-A, HLA-B, HLA-DR locus with a flow cytometry quantification technique. With advancing age, we observed: (i) a significant decrease of the percentage of T cells and B cells expressing HLA-A products; (ii) a decrease of the number of HLA class-I antigenic sites expressed per cell on the three populations tested, predominantly on B cells and in a locus-dependent fashion; (iii) a decrease of the number of HLA-DR molecules expressed per T cell, although the percentage of T cells expressing DR products was increased; (iv) a significant diminution of the percentage of B cells expressing HLA-DR molecules, without changes of the number of HLA-DR antigenic sites per cells. These changes in HLA expression with increasing age could contribute to the decreased level of immunologic responsiveness observed with ageing and contribute to the modification of antigen recognition.

Characterization of two human IgM monoclonal antibodies reactive with HLA-B27

We describe here the generation and characterization of two human monoclonal IgM antibodies (UL-4F11 and UL-F6) reactive with HLA-B27. The monoclonal antibody (mAb) UL-4F11 is cytotoxic for peripheral mononuclear cells and, therefore, useful as typing reagent for HLA-B27 and HLA-B38. Protein chemistry showed that the mAb UL-4F11 precipitates HLA-B27 molecules. Epitope mapping analysis suggests that the amino acids 45, 67, 82 and 83 (alpha-1 domain) of the HLA-B27 sequence are necessary for mAb UL-4F11 reactivity. The mAb UL-F6 is suitable for complement dependent lysis of lymphoblastoid cell lines and stimulated peripheral blood mononuclear cells with HLA-B27 (B*2701, B*2702, B*2703, B*2705, B*2707), B13, B40 (60,61), B47 and B48 specificities. Its reactivity indicates that the amino acid valine in position 152 and glutamic acid in position 163 of the alpha-2 domain are crucial for the binding epitope.

Relative implication of peptide residues in binding to major histocompatibility complex class I H-2Db: application to the design of high-affinity, allele-specific peptides

The H-2Db peptide sequence SMIENLEYM was manipulated (N- and C-terminus truncation and alanine substitution) to determine the role of structural elements (peptide ends and residue side chains) in binding to H-2Db. We found that good binding affinity could be obtained by compensating the minimal binding condition for one element by the optimal condition of the other element. In particular, we showed, that although the minimal binding sequence could be as short as a heptamer (deletion of positions 1 and 2), it needed the presence of optimal amino acids at other positions (IENLEYM). Conversely, the structurally minimal peptide would accept multiple alanine residues, but required the optimal nonameric length (AAAENAEAA). Positions 1, 2, 3, 4, 5, 7 and 9, but not 6 and 8, were involved in the H-2Db-peptide interaction. Most residues interacted directly with the MHC molecule via their main chain (amino and carboxyl) atoms (positions 1 and 2), their side chains (positions 3 and 5), or both (position 9). Positions 4 and 7 were found to play an indirect role, probably by influencing the secondary structure. At the C-terminus, the presence of a residue at position 9, but not the hydrophobic nature of its side chain, was mandatory for binding. At the N-terminus, the role of the residue at position 1 was of either minor or critical importance depending on the presence or not of a strong auxiliary anchor at position 3. The indirect contribution of residue side chains at positions 4 and 7 reflected the importance of dynamic components in the binding process. Based on these results, we designed a series of high-affinity, H-2Db selective peptides derived from the sequence X1 AIX4NAEAL, where X1 = Y or K and X4 = E or K. After radioiodination or fluorescent (FITC) labelling, these peptides bound strongly and specifically to the surface of viable H-2Db-expressing cells. Rationally designed synthetic peptides, either alone or in a stable complex with MHC, might be of value for controlling CTL activity.

Characterization and epitope mapping of four HLA class II reactive mouse monoclonal antibodies using transfected L cells and human cells transfected with mutants of DQB1*0302

To study epitopes of HLA class II molecules, four mouse monoclonal antibodies (mAbs) 13B6, 17F8, 19A1 and 12G6 were made using HLA-DQ8, DP2 and DP4 expressing mouse transfectants for immunization. Three of the mAbs, 13B6, 17F8 and 19A1, bound to all DQ1, 4, 8 or 9 positive B-lymphoblastoid cell lines (B-LCLs) and transfectants tested, i.e. cells carrying the DQB1 genes 0302-3, 0401-2, 0501-3, 0601-4 and 0609 irrespective of the accompanying DQA1 gene. These DQB1 genes code for the shared amino acids (aa) GVY in position 45-47 of the DQ beta chain. DQ1+4+8+9 specific (IIB3) and DQ3 specific (IVD12) reference mAbs inhibited binding of all three mAbs. Testing 13B6, 17F8 and 19A1 with cells made using aa substitutions in various positions of DQ beta 1*0302 indicated involvement of aa 45 in the epitopes of all three mAbs. The last mAb (12G6) bound to all B-LCLs and all DP transfected cells. However, only some DR transfectants and a single DQ transfectant (carrying DQA1*0201 and DQB1*0202) bound mAb 12G6. This reactivity pattern correlates with a shared sequence of aa (RFDSDVGE) in position 39-46 of DR- and DQ- and 37-44 of DP beta chains.

The cytotoxic HLA-DQ3 reactive human hybridoma antibody 4166 that may distinguish DQ7 + 8 from DQ9

The human cytotoxic hybridoma antibody 4166 (IgM kappa) was generated by fusing an in vitro EBV-transformed B-LCL from a multiparous woman with the mouse-human heteromyeloma fusion partner CB-F7. In microcytotoxicity and IIF tests with B-LCLs as target cells, the mAb 4166 was specific for DQ3 (= DQ7 + 8 + 9). However, when used for DQ typing of class-II-positive PBMCs, 4166 could be rendered functionally specific for DQ7 + 8 and did not react with DQ9+ PBMCs. Binding of mAb 4166 to DQ8-positive cells was efficiently blocked by several allotype-specific mAbs recognizing DQ8. Other HLA class-II-specific mAbs were unable to inhibit. With the use of mAb 4166, it is possible to discriminate DQ7 + 8 from DQ9 in serologic DQ typing.

Cells expressing a major histocompatibility complex class I molecule with a single covalently bound peptide are highly immunogenic

The major histocompatibility complex (MHC) class I molecules expressed at the cell surface are associated with a large number of different peptides so that the density of a given MHC-peptide complex is relatively low. Here we describe the properties of MHC class I molecules genetically attached to a single antigenic peptide. Cells expressing these fusion proteins are recognized by T cells specific for the particular MHC-peptide complex. Coculture of naive splenocytes with cells expressing these MHC-peptide fusion proteins and the B7.1 antigen allows the induction of primary cytotoxic T lymphocytes (CTL) in vitro. Injection of these cells into naive mice enhances the frequency of specific CTL precursors and protects against a subsequent challenge with a tumor or a virus bearing the antigenic peptide. Soluble MHC-peptide fusions were also produced in which all three components, that is, the heavy chain, beta 2-microglobulin and the peptide, have fused into a single-chain protein. The availability of MHC class I molecules bound to a single peptide provides valuable tools for the manipulation of CTL responses and the analysis of the selection processes in the thymus.

A human hybridoma monoclonal antibody (TrJ11) recognizing a new HLA-DR epitope shared by DR4, DR8, DR11, and DRB1*1303

The cytotoxic IgM lambda human hybridoma mAb TrJ11 reacts with lymphoblastoid B-cell lines expressing DR4, DR8, DR11, and DRB1*1303. However, TrJ11 was monospecific when normal B cells freshly isolated from blood served as targets in that it only killed HLA-DR4-positive cells. Thus, of 235 HLA-typed persons TrJ11 was strongly cytotoxic for normal B cells of all 90 DR4-positive individuals, but it did not react with B cells from any of the 145 DR4-negative donors. Hence, mAb TrJ11 proved to be suitable for routine DR4 typing. The specific binding of TrJ11 to a DR4-positive cell line was profoundly blocked by the mouse HLA-DR beta chain-specific monomorphic mAb TAL 14.1, indicating that the epitope recognized by TrJ11 is located in the DR beta chain. The possibility that amino acids located in the floor of the peptide-binding site are critical for the TrJ11 epitope is discussed.

Bioengineered soluble HLA-B7. Genesis, characterization, and occurrence of dimerization

A soluble, secreted form of HLA-B7 was engineered by replacing the exons encoding the transmembrane and cytoplasmic domains of the B7 gene with a CI. The modified gene, gsB7, transfected into J27.2 or C1R cell lines, produced a secreted protein, sB7, serologically recognized as B7. Size fractionation showed one species of sB7 at the approximately 55 kD expected for an sB7 alpha-chain-beta 2m heteroduplex, and another at approximately 120 kD which had the same constituent chains and was a dimer of the 55-kD species. Dimer formation appeared to be related to protein concentration but not to disulfide bridging. The sB7 heavy chain on SDS-PAGE showed a doublet at approximately 39 and approximately 42 kD; enzyme analysis indicated that the two bands differed only by a carboxyl terminal polypeptide. Analysis of gsB7 transfectants' mRNA by Northern blots and PCR revealed message fully spliced or with retained CI, accounting for the 39- and 42-kD bands, respectively, and apparently untranslated message with I3 retained. sB7 was not detectable on the surface of gsB7 transfectants by CTLs, nor did it inhibit those CTLs. Production of the sB7 protein provides a ready, consistent source of soluble class I antigen for further study, including test materials for tolerogenicity studies in animal models.

Generation and characterization of a human monoclonal IgG antibody specific for HLA-B12

We describe here the generation and characterization of a human monoclonal IgG antibody (UL/F14) specific for HLA-B12. The antibody is suitable for complement-dependent lysis on lymphoblastoid cell lines and stimulated peripheral blood mononuclear cells. UL/F14 competes for antigen binding with an HLA-B12 human monoclonal IgM antibody and with a specific alloantiserum. Protein chemistry shows that the monoclonal antibody UL/F14 can precipitate solubilized HLA-B12 molecules.

Quantitation of HLA class II antigens on B-cell lines

By quantitation of elutable immunoglobulin G in a recently described ELISA, the number of HLA class I and II molecules on B-cell lines was determined using monomorphic monoclonal antibodies. An average number of 183,000 binding sites per cell for HLA class I-, 99,000 for HLA-DR-, 63,000 for DQ- and 42,000 for DP-specific monoclonal antibodies were determined. The small amount of HLA class II molecules can in part explain the difficulties observed in HLA class II typing or in detection of class II antibodies using the lymphocytotoxicity text.

A human monoclonal hybridoma antibody (TrJ1) specific for HLA-DQ2

TrJ1 is a cytotoxic human hybridoma mAb (IgM lambda). Its reaction pattern with a panel of 42 HLA-defined lymphoblastoid B-cell lines correlated precisely with expression of DQ2. By flow cytometry it was shown that the binding of TrJ1 to DQ2 was efficiently blocked by the murine anti-DQ2 mAb 358.4, indicating that the TrJ1 and 358.4 epitopes overlap. TrJ1 reacted much better with EBV-transformed B cells than with B cells freshly isolated from blood. TrJ1 seemed suitable for typing freshly isolated B cells provided the incubation with complement lasted for 115 min in Terasaki plates. One or more of the DQ2-specific polymorphic amino acids E46, F47, L52, L55, K71 or A74, situated on the alpha-helix of the DQ2 beta chain, are probably critical for the TrJ1 epitope.

Biodistribution and in vivo antitumor efficacy of the systemically administered anti-human T-leukemia immunotoxins and potentiation of their efficacy by alpha-interferon

In this study, the systemically administered anti-human T-leukemia immunotoxins (ITs) are shown to be effective for tumor suppression in Ichikawa T-leukemia-bearing nude mice. In addition, their antitumor efficacy was markedly potentiated by recombinant human IFN-alpha. The combination of ITs and IFN-alpha effectively killed the tumor in the majority of the treated mice; 9 of the 12 treated mice survived tumor-free for as long as they were followed, i.e. for 140 days. Two different ITs, SN1-ricin A chain (RA) and SN2-RA, were used together to minimize the problem of tumor heterogeneity; monoclonal antibodies SN1 and SN2 are directed toward two different human T-leukemia associated cell surface antigens. In the biodistribution experiments, the paired label technique was used to include a reliable internal control. In an experiment, equal amounts of 125I-SN1-RA and 131I-labelled isotype-matching control IgG (IgG1-kappa)-RA were mixed and administered i.v. into tumor-bearing nude mice. In a separate experiment, a mixture of equal amounts of 125I-SN2-RA and 131I-control IgG-RA was administered i.v. This technique allowed us to distinguish the immunospecific uptake from the non-immunospecific uptake of ITs into individual organs. The present results clearly show that both SN1-RA and SN2-RA are specifically localized in tumors after systemic administration. For instance, 24 h after the administration of a radiolabelled mixture, the ratio of 125I/131I in the tumor was 7.0 and 23.5, respectively, for the SN1-RA/control IgG-RA mixture and the SN2-RA/control IgG-RA mixture. Such high ratios of 125I/131I were detected in the tumors throughout the experiments between 30 min and 24 h after the administration of the paired label mixture.

Physical and molecular genetic analysis of Qa-2 antigen expression: multiple factors controlling cell surface levels

We have examined the surface expression of Qa-2 on lymphocyte subpopulations and on splenocytes from inbred mouse strains by a radioactive binding assay using purified anti-Qa-2 antibodies and antibody fragments (Fab). Quantitative measurements by Scatchard analysis revealed that spleen cells from Qa-2high mice express (4-5) x 10(4) Qa-2 molecules/cell, whereas T lymphocytes have as high as (7-8) x 10(4) molecules/cell. In addition, it was determined that B lymphocytes express (5-6) x 10(3) molecules on their cell surface. The Qa-2 levels on anti-CD3-activated T cells is 1.0 x 10(5) molecules/cell. Previous experiments have shown that the quantity of Qa-2 varies in a strain-specific fashion and may be classified into three groups: Qa-2high, Qa-2medium and Qa-2low. Our results indicated that Qa-2high strains express (4-5) x 10(4) Qa-2 molecules/cell, Qa-2medium strains (B6-K2, B10.A, A/J, BALB/c and DBA/2) express (1-1.7) x 10(4) molecules/cell, and Qa-2low strains (SWR/J and DBA/1) express no more than 6 x 10(3) molecules/cell. Detection of Q7 or Q9 mRNA by the polymerase chain reaction revealed that Qa-2high strains express two functional Qa-2 enconding genes, Q7 and Q9, whereas Qa-2medium and Qa-2low strains express either Q7 or Q9. These results strongly suggest that Qa-2 gene dosage contributes in part to the variation of Qa-2 levels on the cell surface.

Equilibrium binding characteristics of monoclonal antibodies recognizing melanoma cell surface antigens

The equilibrium binding characteristics of a panel of six monoclonal antibodies (MAb) recognizing melanoma cell surface antigens (125 kdal cell surface melanoma associated glycoprotein antigen, 125kD-MAA; high molecular weight melanoma associated antigen, HMW-MAA; and a non-protein melanoma associated antigen, NP-MAA) were investigated using the cell lines SK-MEL-2, SK-MEL-5, and M21. The MAbs displayed equilibrium association constant (K) values ranging from 10(7) M-1 to 10(10) M-1 and maximum MAb binding values (Qmax) from 2 x 10(4) to 2 x 10(6) MAb molecules bound per cell. High trypsin concentrations were shown to have deleterious effects on Qmax values obtained for antibodies recognizing the 125kD-MAA, and even low trypsin concentrations affected Qmax values obtained for MAbs recognizing the HMW-MAA (although a complete linear recovery of HMW-MAA antigen was observed in 20-25 hours). Significant changes in Qmax were also noted for different cell passages. Except for MAb 43.2, little variation in K was observed when different cell lines were used. Linear Scatchard plots were obtained for all MAbs except 43.2 in which case concave down behavior was observed suggesting the existence of positive cooperativity between the binding sites of this MAb.

Production of a cytotoxic human monoclonal antibody with specificity for HLA-DR4 and -DRw10 by cells derived from a highly sensitized kidney recipient

A human monoclonal antibody which reacts preferentially with HLA-DR4 and -DRw10 B-cell targets has been produced. A human B-cell line, secreting antibody which reacted preferentially with DR4 and DR1 targets, was derived from a highly sensitized kidney recipient who had rejected two grafts. This line was fused with the mouse myeloma P3X63Ag8.653 and a selected hybridoma cloned. The clones secrete IgM(lambda), which reacts strongly with HLA-DR4 and -DRw10 and more weakly with -DRw14 and a proportion of -DR1 B cells in cytotoxicity assays. Using B-cell lines as targets in cytotoxicity and enzyme-linked immunosorbent assays, the antibody gives a broader pattern of reaction, reacting with HLA-DR1, -DR4, -DR9, -DRw10, -DRw14, and some -DR2 targets. The antibody (NI) is currently in use as a reagent for tissue typing.

Characterization of PPD-specific T-cell lines generated in type I (insulin-dependent) diabetic and healthy individuals

The particular susceptibility to insulin-dependent diabetes mellitus (IDDM) conferred by HLA-DR3,4 heterozygosity has been suggested to be an effect of transcomplementation of HLA class II molecules. To test this hypothesis of special IDDM-specific hybrid determinants and to evaluate the T-cell repertoire towards a specific antigen in IDDM patients we generated a total of 352 PPD-specific T-cell lines by the soft-agar cloning technique and studied their restriction by HLA class II molecules. Of these lines, 227 were from nine IDDM patients, of whom six were DR3,4 heterozygotes, and 125 from 10 healthy controls. Forty-six T-cell lines elicited specific responses in at least two experiments and in addition to T-cell lines demonstrating class-II-restricted PPD specificity, lines with an alloreactivity occurred. HLA-DQ-restricted PPD-specific T-cell lines were not identified and a possible DP restriction (DPw2) was only observed with one line. These data indicate that PPD is preferentially presented to T cells in the context of HLA-DR/Dw. Presentation of PPD by hybrid molecules in IDDM patients or by IDDM-specific class II epitopes recognized by the T-cell lines was not demonstrated. By restriction fragment length polymorphism analysis using a probe for the joining region of the T-cell receptor gamma gene, T-cell lines generated by the soft-agar cloning technique were found to be oligoclonal. It is concluded that soft-agar cloning should be followed by subsequent limiting dilution in order to assure monoclonality. Different preparations of antigen-presenting cells (APC) were tested. In several cases the T-cell lines were not able to respond to PPD presented by Epstein-Barr-virus-transformed lymphoblastoid cell lines (LCL). It was demonstrated that lipopolysaccharides (LPS) of E. coli potently reduce the proliferative response of antigen-specific and alloreactive T cells when T-cell-depleted peripheral blood mononuclear cells (E- cells) were used as APC, whereas only limited inhibition was observed when LCL were used as APC in the presence of LPS. This effect of LPS is suggested to be mediated by increased prostaglandin secretion by monocytes among the E- cells since indomethacin abolished the effect of LPS. This observation may have implications for T-cell cloning procedures since we have found that most commercially available culture media are heavily contaminated with endotoxin.

A sensitive and specific ELISA using monoclonal capture antibodies for the detection of HLA antigens in blood stains

A double antibody ELISA technique is described to detect HLA antigens in extracts of blood stains. The assay involves capture of free HLA determinants using an immobilized monoclonal antibody directed against monomorphic regions of HLA class I and HLA class II antigens. The captured antigens are then detected using alloantisera directed against the polymorphic regions of the captured HLA entities. The technique is able to detect specific HLA-A, B, and DR antigens in extracts prepared from blood smears as well as from dried and freshly thawed lymphocytes. The assay may be of potential use in forensic medicine, particularly in instances where extraction of nucleic acids for fingerprinting is not feasible.

Binding of labelled influenza matrix peptide to HLA DR in living B lymphoid cells

T cells recognize protein antigens as fragments (peptides) held in a defined binding site of class I or class II major histocompatibility (MHC) molecules. The formation of complexes between various immunologically active peptides and different MHC molecules has been demonstrated directly in binding studies between the peptides and solubilized, purified molecules of class II MHC. Studies with intact cells, living or fixed, have not directly demonstrated the binding of the peptides to MHC molecules on antigen-presenting cells, but the formation of such complexes has been shown indirectly through the capacity of antigen-presenting cells to stimulate specific T cells. Here we report evidence that supports directly the binding of radiolabelled influenza matrix peptide 17-29 to products of the human class II MHC locus HLA-DR, on living homozygous B-cell lines, and we show that the kinetics of such binding is much faster with living cells than with fixed cells. Furthermore, whereas the peptide reacts with HLA-DR molecules of all alleles, it binds preferentially to DR1, the restricting element in antigen presentation.

Possible errors in the calculation of cell-binding parameters exemplified by the analysis of the IgG-Fc receptor system

The binding parameters of monomeric and polymeric (immune complex with a molecular weight of 500,000 daltons) rabbit IgG to homologous Fc receptor-bearing alveolar macrophages were estimated, using corrected values for IgG and cell concentrations. Considering the maximum percentage of monomeric IgG binding to cells (2.7%) and the maximum percentage of cells binding monomeric IgG (32%) instead of the IgG and cell concentrations in the initial reaction mixture, a 36-fold increase of the equilibrium constant (K) (from 0.6 x 10(6) L/M to 21.3 x 10(6) L/M) and a 3-fold increase of the maximum number of IgG molecules able to bind to a single cell (n) (from 7.8 x 10(5) to 23.7 x 10(5] were registered. Since more than 60% of the polymeric IgG is bound to 46% of the macrophage population, the values of K (from 10.8 x 10(6) L/M to 15.6 x 10(6) L/M) and n (from 4.3 x 10(5) to 9.4 x 10(5] are only doubled by using the corrected values for IgG and cell concentrations. It results that the cytophilic fraction of the monomeric IgG, representing only 2.7% of total IgG, has a slightly higher affinity for the Fc receptors than the polymeric IgG. By considering the actual number of macrophages which bind IgG it is evident that the number of Fc receptors per cell is higher than that determined by the usual procedure which does not take into account cellular heterogeneity.

Differential expression of HLA class-I antigens on B and T lymphocytes obtained from human lymphoid tissues

The amount of HLA class-I antigens was determined on the surface of enriched populations of B and T lymphocytes obtained from human peripheral blood, lymph nodes and spleens. The assays were performed using monoclonal antibodies that recognize different determinants on HLA class-I antigens and utilizing a simple and sensitive enzyme-linked immunosorbent assay (ELISA). Our results indicate that B lymphocytes obtained from human peripheral blood, lymph nodes and spleens express at least twice as many HLA class-I antigens as T lymphocytes obtained from the same organs.

Association between HLA phenotype and HLA concentration in plasma or platelets

To understand the relationship between HLA phenotype and plasma or platelet HLA better, concentrations of plasma and platelet HLA were measured in 215 individuals of known HLA phenotypes. Precise quantitation of HLA antigens was achieved by means of an enzyme-linked immunoassay using the W6/32 monoclonal antibody and purified HLA molecules. The mean plasma and platelet HLA concentrations were 2.04 +/- 1.67 micrograms/ml (+/- SD, n = 215) and 11.28 +/- 4.65 fg/cell (+/- SD, n = 213), respectively. Statistical analysis of associations between HLA phenotypes and plasma HLA revealed that the mean plasma HLA concentration of individuals with HLA-A23 or HLA-A24 was 1.4 (p less than 0.002) or 1.9 (p less than 0.001) times higher than those without these two HLA antigens. Furthermore, the mean plasma HLA concentration of individuals who have HLA-A26 was 25% less than those without HLA-A26 (p less than 0.05). In contrast, the only association between HLA phenotypes and HLA concentrations of platelets was observed in HLA-B7-positive individuals. The mean platelet HLA concentration of HLA-B7 individuals was 27% higher than those without HLA-B7 (p less than 0.005). This finding is in accordance with previous observations made on red blood cells. The results indicate that the HLA concentrations in plasma are regulated, at least in part, by genetic factors that are different from those regulating platelet HLA.

Analytical studies of the binding parameters describing the interaction of HLA-DR epitopes with a specific monomorphic monoclonal antibody

In this paper we present an analytical study of the binding parameters related to the interactions of the HLA-DR-specific monoclonal antibody (L243) and its reacting epitope as expressed on the cell surface of seven Epstein-Barr virus-transformed B cell lines. Scatchard, Sips and Langmuir equations were used to plot and analyse the data obtained from each reaction. A single affinity constant (K) value was derived at low and high concentrations of free antibody for each antibody-cell interaction tested and was of the order of 10(7) M-1. Similar heterogeneity indices (a) (close to 1.0) and K values were obtained for most of the cells. These results suggest that the reacting HLA-DR epitopes are homogeneously distributed and equally accessible to the antibody on all the cells tested. The average number of epitopes per cell was 3.4 X 10(6), SD 0.5 X 10(6) and were similar for all the cell lines. The analytical and experimental model presented here can be useful for studying quantitative and qualitative variations in the expression of MHC epitopes in oncogenesis and disease associations.

Quantitative estimation of HLA-A and HLA-B antigens carrying the Bw4 supertypic specificity in human peripheral blood lymphocytes

A monoclonal antibody specific for HLA-Bw4 was employed for the quantitative estimation of class I antigens on human peripheral blood lymphocytes and on the human macrophage cell line U 937. The epitopes reactive with the HLA-Bw4-specific antibody, which are present on different antigens coded by the HLA-A or the HLA-B locus, were characterized in terms of equilibrium and kinetic binding parameters. The level of expression of class I antigens on human lymphocytes was found to be in direct proportion to the gene dose. Variations between donors of the same phenotype were of minor importance. Estimation of the association constant, association rate constant, and half-life of dissociation for the interaction of the antibody with lymphocytes heterozygous for either HLA-A24, HLA-A32, HLA-A9, or HLA-Bw4 strongly suggested that the public antigenic determinant shared by these antigens is identical.

Cell surface expression of beta 2-microglobulin (beta 2m) correlates with stages of differentiation in B cell tumours

Cell surface beta 2-microglobulin (beta 2m) densities of malignant B cells were determined by enzyme immunoassay in 97 cases of immunologically defined lymphoproliferative disease. Absolute beta 2m densities were found to depend on disease category with the lowest levels found on cells from chronic lymphocytic leukaemia (mean = 5.6 ng/10(6) cells, n = 27); atypical chronic lymphocytic leukaemia (mean = 5.9 ng/10(6) cells, n = 8); and prolymphocytoid chronic lymphocytic leukaemia variant (mean = 6.0 ng/10(6) cells, n = 16). beta 2m densities for B non-Hodgkin's lymphoma (n = 14) and B prolymphocytic leukaemia (n = 17) cases were 8.1 and 10.0 ng/10(6) cells, respectively, and the highest densities were found on cells from "late-B cell" tumours (mean = 14.3 ng/10(6) cells). Plasma cells from cases of Ig secreting tumours expressed unexpectedly low beta 2m densities (mean = 9.3 ng/10(6) cells; n = 6).

A human monoclonal antibody against HLA-A25

We are reporting the production and characterization of a human monoclonal antibody recognizing antigen HLA-25. The antibody was developed by a line transformed in vitro by the Epstein-Barr virus. The immune B lymphocytes for transformation were generated by planned immunization of a volunteer with repeated doses of allogenic peripheral blood lymphocytes of one donor over the course of 7 years. The antibody showed correlation with A25 antigen on a panel of 244 individuals tested by microcytotoxicity. The antibody showed neither cytotoxic reactivity nor CYNAP phenomenon with antigens of HLA-10 CREG.

A human monoclonal antibody to an HLA-DRw53 (MT3)-like epitope on class II antigens

We report the production of a lymphoblastoid human B cell line, which secretes monoclonal antibody with HLA-DRw53-like specificity. The immune lymphocytes were obtained from a patient who had been undergoing immunotherapy at Memorial Hospital with allogeneic cultured melanoma cells. The antibody producing cell line was established by transformation of immune B cells with Epstein-Barr virus and stabilized by serial selection of antibody-positive cell clusters. The cell line (R39.14) has been producing a cytotoxic antibody of IgM, kappa type during nearly two years of continuous culture. The specificity pattern was determined on a panel of HLA-DR-typed lymphoblastoid cell lines, and resembled the HLA-DRw53 specificity closely. In studies of informative families the R39.14 specificity segregated with DRw53-bearing haplotypes, which included DR-4, 7 and DRw9 antigens. The R39.14 specificity was found to be expressed in similar quantities on all antibody positive homozygous cell lines tested. Blocking experiments with monoclonal class II specific antibodies revealed R39.14 to reside on a DR molecule in close association with the determinant detected by the 109d6 mouse monoclonal antibody.

Comparison of MHC antigen expression on PHA- and MLC-induced T cell lines with that on T and B lymphoblastoid cell lines by cell cycle dependency

Although it is well known that the expression of major histocompatibility complex (MHC) antigens on the surface of lymphoblastoid cell lines are cell cycle dependent, the way in which the MHC antigen expression on activated T cells varies with cell cycle phase has not previously been described. Using 11 lymphoblastoid cell lines from malignant and nonmalignant tissues (B cells, T cells, and myeloid cells) and five activated T cell lines (two cell lines activated by phytohemagglutinin and three alloreactive T cell clones), MHC antigen expression was quantitatively studied by dual-beam flow cytometry. Correlated measurements of surface antigen quantity (immunofluorescence), DNA content (Hoechst 33342), and cell size (light scatter), uninfluenced by induction synchrony and cell fixation, were performed. The data indicate that cell surface antigen quantity and cell surface area demonstrate specific values at each phase of the cell cycle when the cells are in logarithmic growth. Examining cells in logarithmic growth, it was confirmed, for all lymphoblastoid cell lines, that the quantity of MHC antigens on G2 (S + G2 + M) cells was greater than that on G1 cells. In addition, it was found, by analyzing antigen quantity and surface area, that class I antigen density in the G2 phase is 17% less than that in the G1 phase in leukemic T cell lines, and that both class I and class II antigen densities in the G2 phase were 21% less than that in the G1 phase in lymphoblastoid B cell lines. In activated T cells, class I antigen density in the G2 phase was 11% less than that in the G1 phase, while class II antigen density in the G2 phase was 12% greater than that in the G1 phase. We describe four important observations in this report. In both G1 and G2 phases, activated T cells express: quantitatively fewer class I antigens than lymphoblastoid B cell lines; similar quantity of class I antigens as that of leukemic T cell lines; and similar quantity of class II antigens as that of lymphoblastoid B cell lines. Also, class II antigens are expressed in greater density in the G2 phase than in the G1 phase in activated T cells. In contrast, lymphoblastoid B cell lines express greater density of class II antigens in the G1 phase than in the G2 phase of the cell cycle. These findings differ from previous reports, suggesting that G1 phase cells may have a more significant role than G2 phase cells as target cells for MHC restricted cytotoxic cells.

Anti-immunoglobulin stimulation of human B lymphocytes is inhibited by anti-class II major histocompatibility complex antibodies

The effect of murine monoclonal antibodies binding monomorphic epitopes of Class II, HLA-DR molecules on responding human B lymphocytes stimulated by anti-immunoglobulin M (IgM) antibodies was studied. Goat F(ab')2 anti-human IgM coupled to Sepharose beads (insoluble), or in solution, was added to macrophage-depleted B cells in culture with, or without, anti-human HLA-DR monoclonal antibodies. The addition of monoclonal anti-HLA-DR antibodies to anti-human IgM-stimulated B lymphocytes inhibited this T-independent B-cell proliferation by 82-94%. The role of Class II, HLA-DR molecules on B cells may therefore exceed that of antigen presentation alone, to include responding B-cell activation induced by anti-immunoglobulin.

Leu-7-positive cells with monocyte phenotype show different ultrastructural features in comparison to Leu-7-positive cells with T-cell phenotype

The ultrastructural features of the Leu-7-positive - Leu-M3-positive cell subpopulation and the Leu-7-positive - Leu-4-positive cell subpopulation were characterized and compared using immunogold-immunoperoxidase double labelling with immunoelectron microscopy. The majority of Leu-7-positive cells coexpressed a monocyte phenotype and showed an ultrastructural pattern specific for functional natural killer (NK) cells, i.e. a low nuclear/cytoplasmic (N/C) ratio, an irregular outline, many cytoplasmic organelles and electron-dense granules. In contrast, only a minority of Leu-7-positive cells coexpressed a T phenotype, and these were characterized by a high N/C ratio, an even surface and the absence of electron-dense granules. Thus, Leu-7-positive - Leu-4-positive cells may by an immature form of NK cells, and Leu-7-positive - Leu-4-positive and Leu-7-positive - Leu-M3-positive cell subpopulations may represent different stages of Leu-7-positive cell differentiation.

Natural HLA antibodies

"Natural antibodies" directed against antigens of the Major Histocompatibility Complex have been observed in aged mice but very seldom in humans. It is likely that HLA natural antibodies are more common than previously supposed: our results suggest they may be found in 1% of normal blood donors. Most of these antibodies seem to be weak and can only be detected when B lymphocytes (BL) are used as target cells in the lymphocytotoxicity technique or when indirect immunofluorescence is used with peripheral blood lymphocytes (PBL). The behavior of these natural IgM antibodies was compared to that of weak immune IgG HLA antibodies detected in the same way. Absorption tests showed that "natural antibodies" were very specifically absorbed, whereas "immune antibodies" could also be absorbed by cells not carrying the specific antigen. Furthermore, about half of the "natural antibodies" detected to date carried the HLA-B8 specificity. Various hypotheses have been put forward to attempt to explain the appearance of these antibodies.

HLA typing of Epstein-Barr virus transformed lymphoblastoid cell lines (LCL)

The application of standard tissue typing techniques to cells other than peripheral blood lymphocytes has been accompanied by the problem of extra reactions. This applies as well to Epstein-Barr virus transformed lymphoblastoid cell lines (LCL) as to leukemic cells and human spleen cells. These extra reactions are attributable to additional antibodies in the typing sera which are not apparent under standard conditions with PBLs. Two types are described: Type 1 extras, which becomes apparent after longer incubation times and are attributed to weak antibodies and type 2 extras which are apparent after shorter incubation times and are attributed to subpopulation specific or differentiation antigens. Technical modifications are proposed by which these extras can be circumvented. They include: Only start typing when cells have been cultured for 2 to 3 days. Remove dead cells by spinning over standard ficoll-hypaque or 11% triosil. Use shorter incubation times. Avoid using sera that give too many type 2 extras. In this way phenotypes can be accurately identified on LCL's obtained from kidney transplant donors and recipients. When LCL's were compared with their matching PBL, HLA phenotypes were concordant in 87% of cases for HLA-A, 90% for HLA-B, 81% for HLA-C and 70% for HLA-DR.

beta 2-Microglobulin secretion from lymphoid cells: a study at the cellular level

A protein plaque assay was developed for the detection of human lymphocytes secreting beta 2-microglobulin. The development of plaques required production of beta 2-microglobulin by viable cells at an estimated rate exceeding 25 molecules per second. It has previously been suggested that beta 2-microglobulin secretion is restricted to certain lymphoid cell subpopulations. However, both T- and B-cells were shown to form plaques in normal donors and immunodeficient patients after activation with various mitogens. A close correlation between beta 2-microglobulin production and DNA synthesis was evident. However, secretion of immunoglobulin did not correlate with the proportion of cells secreting beta 2-microglobulin.

Detection of antibodies to cell surface antigens by a simplified cellular ELISA (CELISA)

An improved method for screening human hybridoma antibodies to cell surface antigens is described. The following modifications have been developed: rapid expansion of desired screening cell types by EBV transformation; use of only 5 X 10(4) cells/well; elimination of the need for glutaraldehyde fixation; elimination of the requirement for PLL to attach cells to microplates; preparation of a large number of plates which can be stored at 4 degrees for 3 months; Protein A-peroxidase ELISA assay yielding excellent replicates, low background "noise", and high OD readings for positive wells. The techniques we have developed should greatly simplify and shorten the assay procedures for detecting human antibodies to a variety of cell surface antigens.