Crystal structure of an HIV-binding recombinant fragment of human CD4

CD4 glycoprotein on the surface of T cells helps in the immune response and is the receptor for HIV infection. The structure of a soluble fragment of CD4 determined at 2.3 A resolution reveals that the molecule has two intimately associated immunoglobulin-like domains. Residues implicated in HIV recognition by analysis of mutants and antibody binding are salient features in domain D1. Domain D2 is distinguished by a variation on the beta-strand topologies of antibody domains and by an intra-sheet disulphide bridge.

Intraperitoneal recombinant gamma-interferon in patients with recurrent ascitic ovarian carcinoma: modulation of cytotoxicity and cytokine production in tumor-associated effectors and of major histocompatibility antigen expression on tumor cells

Seven patients with advanced epithelial carcinoma and ascites, relapsing after two or more regimens of standard chemotherapy, have been treated with recombinant gamma-interferon (rIFN-gamma) i.p., via a permanent catheter. rIFN-gamma (Immuneron; Biogen; 0.5 mg = 10(7) IU in 2 liters of saline) was administered 3 times a week, on alternate weeks, for a total of nine courses. No major toxicities were observed: mild fever, malaise, and a flu-like syndrome occurred in all patients. The modulation of immunological parameters was studied. Cytotoxic activity of immunocompetent cells against tumor cell lines was measured both in the peritoneal compartment and in peripheral blood mononuclear cells. A significant increase of cytotoxicity of tumor-associated macrophages was observed in 5 of 7 patients and in 4 of 7 patients with tumor-associated peritoneal lymphocytes. Circulating effector cells were only occasionally stimulated. Tumor-associated macrophages isolated from the ascitic fluid and stimulated with lipopolysaccharide produced higher amounts of interleukin 1 in 5 of 6 patients tested, while interleukin 6 production by unstimulated tumor-associated macrophages was augmented in 2 of 2 patients after rIFN-gamma treatment. Freshly isolated ovarian carcinoma cells from the ascitic fluid has a variable, although usually low, expression of HLA-DR antigens. rIFN-gamma treatment caused a marked increase in HLA-DR expression in all patients tested. Expression of HLA class I antigens was negative in 2 of 5 patients and was strongly increased in 1 of the 2 after treatment. The observation that rIFN-gamma administered i.p. activates in situ effector cells and augments major histocompatibility antigen expression in tumor cells, with minimal toxicity, encourages further efforts to investigate its therapeutic potential in ovarian carcinoma.

Human peripheral blood dendritic cells concentrate in contrast to monocytes intracellular HLA class II molecules in a juxtanuclear position

The localization of histocompatibility antigens of the HLA-D locus in dendritic cells (DC) and monocytes (Mo) isolated from human peripheral blood was investigated. Functionally DC were characterized by their capacity to act as strong stimulators in an allogeneic mixed leucocyte reaction. In cytospins, DC were differentiated from Mo by dendritic morphology, strong HLA class II and moderate RFD1 expression on the plasma membrane and acid phosphatase activity in a juxtanuclear spot. Ultrathin cryosections showed that DC had a heavily labelled plasma membrane for HLA-D. In addition, these antigens were found in intracellular vesicles predominantly located in the juxtanuclear zone. This pattern of labelling was not seen in Mo. Obviously, DC concentrate intracellular class II antigens in the same area as lysosomal activity. These results may indicate that this juxtanuclear area is a center of antigen processing in DC.

HLA-D determinants are expressed on human seminal cells other than spermatozoa but not on purified spermatozoa

Purified human spermatozoa do not regularly stimulate lymphocytes in spermlymphocyte cultures (SLC). This lack of consistent stimulation was found not to be dependent on sperm/lymphocyte ratio or on culture peak response time. A few weak stimulations obtained are not HLA-D or sex dependent. Contaminating seminal cells other than spermatozoa (SC non-SZ) may be responsible for the high stimulations found in SLC by others, since, in our hands, purified suspensions of SC non-SZ stimulate allogeneic lymphocytes in an HLA-D-dependent fashion, and such responses are abrogated by anti-HLA-DR monoclonal antibodies. These functional data confirm our previous finding of HLA-DR molecules on SC non-SZ by absorptions (and a lack of expression on spermatozoa) and suggest the concomitant expression of HLA-DQ and -DP products.

Evidence of T-cell activation and potential cytokine action in human endometrium

Antigenic epitopes have been described whose expression characterizes early or late stages of activation of T-cells. In this study the expression of early activation antigen, interleukin-2 receptor was compared with the expression of late activation antigens, HLA-DR, HLA-DP, and HLA-DQ molecules of the major histocompatibility complex II, and very late activation antigen, VLA-1 of the integrin superfamily of molecules in 43 human endometria. These molecules were localized by their reactivity with monoclonal antibodies in an avidinbiotin-complex procedure. Interleukin-2 receptor was not expressed in human endometria; however, endometrial T-cells within lymphoid aggregates, some scattered in endometrial stroma and a few within epithelium, expressed HLA-DR, HLA-DP, HLA-DQ, and VLA-1. In addition, expression of the receptor of interferon-gamma, a product of activated T-cells, was observed on endometrial epithelium. Evidence for activation of T-cells and expression of interferon-gamma receptor in human endometrial epithelium suggests that endometrium may be an active site for cytokine action.

Invariant chain trimers are sequestered in the rough endoplasmic reticulum in the absence of association with HLA class II antigens

HLA class II antigens are heterodimeric cell surface glycoproteins that interact with antigenic peptides to form complexes recognizable by CD4-positive T cells. During their biosynthesis, class II antigens are retained in a post-Golgi compartment in association with the invariant chain, which dissociates before class II cell surface expression. To address whether the invariant chain mediates this post-Golgi retention, its transport and assembly were examined in cells that do not express HLA class II antigens. Pulse-chase analysis and endoglycosidase digestions showed that very little invariant chain proceeded as far as the trans-Golgi in class II-negative cell lines. Immunofluorescence studies suggested that in these cells the invariant chain is sequestered in the RER. Gel filtration and cross-linking data showed that RER-localized invariant chain is present as trimers or aggregated trimers. Multimerization is mediated by lumenal interactions; a proteolytic fragment of the invariant chain corresponding to the lumenal domain remained trimeric as determined by cross-linking analysis. Similar transport and structural characteristics were observed for a pool of excess invariant chain in class II-positive cells, suggesting that an excess of invariant chain in the ER may be important for class II antigen function. These results have important implications for the transport of cellular proteins in general and for the role of the invariant chain in class II antigen biosynthesis.

Intracellular transport and peptide binding properties of HLA class II glycoproteins

Protein antigens internalized by an antigen presenting cell are degraded into peptides, a subset of which binds to the class II glycoproteins encoded by the major histocompatibility complex to form epitopes recognized by specific T cells. Current evidence suggests that the immunogenic peptides are generated in an endosomal, acidic compartment containing internalized antigen, proteinases, and exocytic class II molecules. These exocytic class II glycoproteins are associated during transport from the endoplasmic reticulum to the endosomal compartment with an additional glycoprotein, the invariant chain. Proteolytic degradation of the invariant chain in the endosomal compartment dissociates it from the class II glycoproteins, which only then acquire the capacity to bind peptides. After peptide binding occurs, the class II-peptide complexes are transported to the antigen-presenting cell surface for recognition by T cells.

Granulocyte-macrophage colony-stimulating factor stimulates human monocyte accessory cell function

We investigated the effect of recombinant human granulocyte-macrophage CSF (rhGM-CSF) on the accessory cell function of purified human monocytes. Compared with untreated monocytes, rhGM-CSF-treated monocytes promoted enhanced mitogen- and Ag-stimulated lymphocyte proliferation. This enhancement was significantly inhibited by mAb to rhGM-CSF. In experiments designed to define the mechanism of rhGM-CSF augmentation of accessory cell function, rhGM-CSF was shown to cause a dose-dependent increase in monocyte expression of surface HLA-DR molecules and stimulated secretion of IL-1, both important in monocyte T cell interactions. Further studies demonstrated that levels of HLA-DR and IL-1 mRNA were increased by rhGM-CSF, indicating transcriptional regulation of gene expression for HLA-DR and IL-1. Thus, rhGM-CSF augments accessory cell function by human monocytes, and this augmentation correlates with rhGM-CSF-induced increases in transcription of the HLA-DR and IL-1 genes leading to increased expression of surface HLA-DR and secretion of IL-1.

HLA expression in hemopoietic development. Class I and II antigens are induced in the definitive erythroid lineage and differentially modulated by fetal liver cytokines

We investigated the expression of HLA Ag on hemopoietic progenitors (burst-forming unit E, CFU-E, and CFU-granulocyte-macrophage) and precursors from human embryonic fetal liver (FL) and peripheral blood at 5 to 9 wk postconception. The expression on progenitors was evaluated by complement-mediated cytotoxicity followed by assay of residual progenitors in clonogenic culture; immunofluorescence and RIA were used for differentiated precursors. HLA Class I and II Ag are not expressed on the primitive erythroid lineage, i.e., on yolk sac-derived megaloblasts circulating in 5- to 6-wk peripheral blood. However, they are gradually induced on the definitive erythroid lineage in FL. Their expression on progenitors is first detected at 6 wk and shows a progressive increase through 9 wk, up to greater than or equal to 50% of adult values. A similar expression pattern is observed for FL erythroblasts. Incubation of 6-wk FL erythroid cells with IFN-alpha, -beta, or -gamma, or TNF-alpha induces a sharp rise of the expression of HLA class I, but not HLA class II Ag on both progenitors and precursors. In contrast, incubation with PHA-stimulated adult leukocyte-conditioned medium causes a marked increase of both HLA-ABC and HLA class II Ag expression. We hence investigated the effect of cytokines present in leukocyte-conditioned medium on the expression of HLA class II Ag: although IL-1 alpha, IL-2, and granulocyte-macrophage-CSF do not exert a significant action, IL-1 beta and IL-4 induce a marked increase of HLA class II, but not class I, Ag expression on 6-wk FL progenitors and precursors. Low amounts of IFN-gamma, TNF-alpha, and IL-1 beta were detected in the supernatants and extracts of 6-wk FL cells. The concentrations of these cytokines in both supernatants and extracts sharply increase in the 7- to 8-wk period, particularly for TNF-alpha and IL-1 beta, thus indicating a direct correlation with the rise of HLA Ag expression on FL erythroid cells in the same period. In conclusion, the expression of HLA class I and II Ag is not detected on primitive megaloblasts, but is gradually induced on definitive FL progenitors and precursors, possibly via production of specific cytokines in the FL microenvironment, i.e., IFN-gamma and TNF-alpha for class I Ag and IL-1 beta for class II Ag.

Altered signal transduction secondary to surface IgM cross-linking on B-chronic lymphocytic leukemia cells. Differential activation of the phosphatidylinositol-specific phospholipase C

To further study the mechanisms by which surface Ig triggering activates the inositol phospholipid signaling pathway, we have used B cells from chronic lymphocytic leukemia patients which, as previously described, display two patterns of response upon sIg cross-linking: in one group this cross-linking induces an inositol phosphate release, an intracellular free Ca2+ concentration elevation and a subsequent cell proliferation; in a second group none of these events occur although there is an increased class II Ag expression following anti-mu stimulation as in the first group. We have been able to demonstrate that the phosphatidyl inositol specific phospholipase C (PI-PLC) can be activated in permeabilized B cells from the first group by direct stimulation, with GPT gamma S, of a guanine nucleotide binding (G) protein. In addition, since anti-mu + GTP gamma S stimulate an increased inositol phosphate production in these cells, this suggests that surface Ig cross-linking activates PI-PLC via a G protein. However, in cells from the second group no inositol phosphate is released after GTP gamma S stimulation although PI-PLC can be directly activated by high Ca2+ concentrations. This reflects in these cells, an interruption of the signaling cascade sIg/G protein/PI-PLC at the level of the G protein or at the G protein/PI-PLC coupling. In cells from both groups PMA treatment, which is known to alter phosphatidyl inositol metabolism in B cells, completely inhibits PI-PLC activation even by high Ca2+ concentrations. These studies show that the phosphatidyl inositol-dependent signaling cascade after surface Ig triggering can be altered at different levels in B cells.

HIV-gp120 can block CD4-class II MHC-mediated adhesion

A possible component of the immune dysfunction associated with infection by HIV is the inhibition of CD4 function resulting from the avid binding of soluble HIV envelope glycoprotein (gp120) to cell surface CD4. We assessed CD4 function by measuring the ability of CD4+ T cells to form conjugates with cell size lipid vesicles, artificial target cells (ATC), bearing the natural ligand for CD4, MHC class II proteins. Conjugate formation was a transient process with the greatest number of specific cell to ATC conjugates found after approximately 30 min of incubation at 37 degrees C. Addition of gp120 specifically blocked conjugates between CD4+ cells and class II ATC in a concentration-dependent manner. These data indicate that T lymphocyte adhesion mediated by CD4 is a dynamic event and that binding of gp120 to CD4 is able to disrupt the normal progression of the interaction between CD4+ T lymphocytes and class II+ APC.

Modulation of the HLA class II antigen at a molecular level by maternal serum

The recent immunological literature has described the existence of a retroplacental serum factor being responsible for the downregulation of the MHC Class II antigen expression. In this report, the same property has been found in peripheral maternal serum. The HLA Class II modulating activity is however diminished in the presence of peripheral maternal serum as compared to retroplacental serum suggesting that the IA like inhibiting factor is released at the fetomaternal interface. After a three-day incubation period of unrelated lymphocytes in a maternal serum pool, it was shown that the HLA Dr., the HLA Dp., and more significantly, the HLA Dq. molecules were modulated. When third party lymphocytes were stimulated by Candidine or unrelated mononuclear cells in the presence of retroplacental serum, only the cellular subpopulation belonging to the CD4+ subset showed an HLA Dq. downregulation. The molecular constituents of the MHC Class II antigen expression characterizing cells belonging to other subsets remained unchanged. When the same stimulation assay was performed in the presence of a control medium (nulliparous serum), no changes concerning the MHC Class II molecular constituents were observed. When unrelated mononuclear cells were PHA stimulated in the presence of maternal and nulliparous serums, the HLA Dq. expression of the CD8+ subset showed a significant downregulation in the maternal serum mediated stimulation assay as compared to the control stimulation test. The molecular expression of the HLA Class II antigen related to the other subpopulations (CD4+, CD3+) stimulated by a mitogenic lectin remained unchanged. It is suggested that these molecular MHC Class II modulations are due to a factor included in the maternal IgG reaction. Retroplacental IgG contains the highest concentration of this factor.

Further evidence for a human B cell activating factor distinct from IL-4

Supernatants from activated human T cell clones were previously shown to contain B cell-activating factor (BCAF), an activity which results in polyclonal resting B cell stimulation. In the present study, we investigate the relationship between this activity and human interleukin-4 which was also shown to act on resting B cells. The supernatant of the T cell clone TT9 contains IL-4 but anti-IL-4 antiserum does not affect the response of B cells as measured by thymidine uptake or cell volume increase. Furthermore, IL-4 induces Fc epsilon-receptor (CD23) expression on 30% of unstimulated human B cells, whereas BCAF-containing supernatants from clone P2, that do not contain detectable amounts of IL-4, promote B cell proliferation without inducing CD23 expression. Our results therefore establish that IL-4 and BCAF are distinct activities and suggest that they trigger different activation pathways in human B cells. In addition, culture of B cells with T cell supernatants for 72 hr induces a three- to fourfold increase in the expression of HLA-DR, -DP, and -DQ antigens in 50% of B cells. The addition of inhibiting concentrations of anti-IFN-gamma, LT, or IL-4 antisera to the cultures does not change these results. Finally, 30% of B cells cultured with T cell supernatants leave the G1 phase of the cell cycle and 20% reach mitosis. Taken together, our findings further support the existence of a B cell-activating factor responsible for the activation of resting human B cells.

Peptides recognized by class I restricted T cells also bind to MHC class II molecules

The mechanisms of antigen recognition employed by both class I and class II MHC-restricted T cells are very similar, yet many of the T cell determinants described to date are recognized in the context of a single class of MHC molecules, and generally with only one or a very few different MHC alleles. To determine whether this might be due to a structural difference between class I and class II restricted T cell determinants, peptides previously shown to be recognized in the context of MHC class I proteins by mouse or human CD8+ T lymphocytes were tested for their capacity to bind to HLA-DR molecules on the surface of B lymphoblastoid cell lines (B-LCL). Four out of five class I restricted T cell determinants tested bound to a panel of B-LCL, and the binding was inhibited by anti-HLA-DR mAb. The peptides did not bind to the class II-negative B-LCL RJ2.2.5 nor to mouse L cells, but did bind to L cells transfected with HLA-DR1.

Different staphylococcal enterotoxins bind preferentially to distinct major histocompatibility complex class II isotypes

The stimulation of T cells by staphylococcal enterotoxins (SE) is strictly dependent on major histocompatibility complex (MHC) class II-bearing cells. The interaction between SE and MHC class II molecules was studied on the human B cell lymphoma Raji and its MHC class II-negative variant RJ 2.2.5. Affinity purification with SEA and SEB matrix allowed the isolation of HLA-DR-like molecules from detergent lysates of 125I surface-labeled Raji cells, but not from RJ 2.2.5 cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis also revealed preferences in the binding of other SE such as SED, SEE and toxic shock syndrome toxin 1 to DR-like molecules, SEC2 to HLA-DQ-like molecules and SEC3 to DR- and DQ-like molecules. Preadsorption of the different MHC class II MHC isotypes confirmed the preferential binding of SEA to DR and of SEC2 to DQ. The implications of these findings for the understanding of SE-induced T cell activation and the potency of SE as a tool in the study of MHC class II antigens are discussed.

Class II MHC molecules and the HIV gp 120 envelope protein interact with functionally distinct regions of the CD4 molecule

A murine T cell hybridoma with a receptor specific for the class I molecule H-2 Dd was transfected with an expressible cDNA for human CD4. Expression of the human class II MHC molecule HLA-DP on Dd-positive murine fibroblasts resulted in a greatly enhanced response of the CD4-positive T cell hybridoma, measured either by lymphokine production or by rosette formation. Inhibition of these functional assays with anti-CD4 monoclonal antibodies implicated the two amino-terminal domains of CD4 in an interaction with the HLA-DP molecule. This interaction was blocked by incubation with recombinant gp120 envelope protein of HIV. In contrast, recombinant soluble CD4 did not inhibit and was able to prevent the inhibition by gp120. Anti-CD4 antibody blocking experiments clearly indicated that distinct regions of CD4 interact respectively with gp120 and with class II MHC molecules.

The invariant chain is a phosphorylated subunit of class II molecules

The phosphorylation of the MHC, class II-associated invariant chain (gamma) is demonstrated in human B-lymphoblastoid, melanoma, and histiocytic lymphoma cell lines. Two-dimensional nonequilibrium gel electrophoresis of invariant chain and class II Ag immunoprecipitates isolated from [32P]orthophosphate-labeled cells demonstrates labeling of both free and class II-associated gamma, gamma s, and p41 forms of the invariant chain. The gamma 2/gamma 3 form of the invariant chain is not phosphorylated. Phosphoamino amino acid analysis of isolated invariant chain shows phosphorylation of serine residues. The isolation of invariant chain from 32P-labeled microsome preparations digested with proteinase K demonstrates that the phosphorylation occurs in the cytoplasmic tail. Limited proteolysis of [32P]orthophosphate-, [35S]cysteine-, and [35S]methionine-labeled invariant chain also indicates that the 32P-label is incorporated into the cytoplasmic domain. These results pinpoint serine residues at positions 9, 26, and 29 in the N-terminal cytoplasmic tail as potential sites for the phosphorylation of the invariant chain. Phosphorylation may be another mechanism by which the functions of invariant chain in class II-dependent immune responses are regulated.

Physical association between MHC class I and class II molecules detected on the cell surface by flow cytometric energy transfer

The physical association of HLA class I and class II Ag in the membranes of PGF and JY lymphoblastoid cell lines was studied using flow cytometric energy transfer. This technique measures the proximity of cell surface molecules in the nm range and provides a distribution histogram of the average proximity of molecules on each cell of a population. HLA Ag were labeled with mAb conjugated to fluorescein, serving as donor, or tetramethylrhodamine, serving as acceptor molecules. Significant fluorescence energy transfer was detected between various combinations of class I and class II molecules indicating that these molecules are within 10 nanometers of each other. Specifically, energy transfer was observed between class I molecules and DR, DQ, or DP class II HLA molecules. In addition, energy transfer between all combinations of DR, DQ, and DP molecules was observed. No transfer was observed among class I molecules or among DR or among DP molecules. Among DQ molecules, subpopulations transferred fluorescence energy to each other. The close contact measured between class I and class II Ag correlates with previous reports of cocapping and may reflect an immunologically significant interaction or the reported tendency of class I Ag to associate with other cell surface receptors, including growth factor receptors. The energy transfer between fluorescent antibodies to class II Ag suggests the existence of heterodimers formed from the different locus products, as well as possible quaternary surface interactions between alpha/beta complexes from separate loci.

Gamma-IFN induces a differential expression of HLA-DR, DQ and DP antigens on peripheral blood myeloid leukemic blasts at various stages of differentiation

Using specific monoclonal antibodies and the indirect immunofluorescence technique, peripheral blood myeloid leukemic blasts from 49 patients were studied for DR expression, 42 for DQ and nine for DP after four days of culture without and with gamma-IFN. The expression of class II molecules on untreated cells depended upon the stage of differentiation and was maximal for DR antigens and lower for DP, while DQ was present only in a small percentage of M2, M4 or M5 blasts. M3 blasts lacked both DR and DQ. Maximal increase of surface expression induced by gamma-IFN was observed for DR molecules independently from the differentiation stage. No significant modification was seen for DQ. Preliminary data concerning DP indicate an increased expression in some of the tested samples. Thus the results obtained on peripheral blood blasts parallel previous observations on leukemic cell lines.

Structural analysis of a peptide--HLA class II complex: identification of critical interactions for its formation and recognition by T cell receptor

An assay for the binding of peptides to major histocompatibility complex (MHC) class II proteins on the surface of cells has been used to determine the relative importance of the amino acids composing an influenza haemagglutinin T cell determinant in binding. The important contact residues were identified by the effect substitution of each residue with biotinylated lysine had on the ability of the peptide to bind. The spacing of the critical residues within the peptide sequence was consistent with the central core, of approximately eight amino acids, adopting a helical conformation. The terminal residues were less constrained and might not be part of a regular conformation. Increasing the helical propensity of the determinant, by simply acetylating and amidating the peptide, resulted in an analogue that was able to stimulate a specific T cell clone at significantly lower concentrations than the natural sequence. A potential location for the peptide in the binding site was postulated based on the presence of complementary amino acids in the class II molecule and supported by screening a large number of peptide analogues for their ability either to bind the restriction element or to stimulate T cell proliferation.

Progression of autoimmune damage in primary biliary cirrhosis: an immunohistochemical study

Aberrant MHC Class II antigen expression and the nature of the infiltrating lymphoid cells were studied by immunohistochemical techniques in liver biopsies from 37 patients with Primary biliary cirrhosis (PBC) (11 histological stage I, 13 stage II-III, 13 stage IV) and 15 patients with chronic non autoimmune liver disease. Bile duct epithelial cells expressed HLA-DR, DP and DQ antigens in biopsies from patients with early (Stage I) PBC and less frequently in the late cirrhotic phases of the disease (Stage IV); these observations support the hypothesis that induction of Class II antigens on epithelial cells may be involved in initiating autoimmune responses towards bile duct components. The presence of cytotoxic/suppressor T cells around the bile ducts in Stage I suggests a role for cell mediated destruction of the ducts at this early stage. The nature of the chronic inflammatory cell infiltrate in the portal tracts, periportal areas and lobular parenchyma does not establish the mechanism(s) involved in disease progression. However, the lack of Class II antigen expression on hepatocytes is compatible with the hypothesis that hepatocellular damage is non-specific and may be secondary to the initial bile duct injury.