Induction of regulatory T-lymphocyte responses by liposomes carrying major histocompatibility complex molecules and foreign antigen

Biomaterial-enhanced treg cell immunotherapy: A promising approach for transplant medicine and autoimmune disease treatment

Regulatory T cells (Tregs) are crucial for preserving tolerance in the body, rendering Treg immunotherapy a promising treatment option for both organ transplants and autoimmune diseases. Presently, organ transplant recipients must undergo lifelong immunosuppression to prevent allograft rejection, while autoimmune disorders lack definitive cures. In the last years, there has been notable advancement in comprehending the biology of both antigen-specific and polyclonal Tregs. Clinical trials involving Tregs have demonstrated their safety and effectiveness. To maximize the efficacy of Treg immunotherapy, it is essential for these cells to migrate to specific target tissues, maintain stability within local organs, bolster their suppressive capabilities, and ensure their intended function's longevity. In pursuit of these goals, the utilization of biomaterials emerges as an attractive supportive strategy for Treg immunotherapy in addressing these challenges. As a result, the prospect of employing biomaterial-enhanced Treg immunotherapy holds tremendous promise as a treatment option for organ transplant recipients and individuals grappling with autoimmune diseases in the near future. This paper introduces strategies based on biomaterial-assisted Treg immunotherapy to enhance transplant medicine and autoimmune treatments.

There is more than one interleukin 1

In 1972, Gery and co-workers(1) detected a factor that promotes murine thymocyte proliferation in culture supernatants of human peripheral blood adherent leukocytes. This factor is active across species lines, does not support the growth of interleukin 2 (IL-2)-dependent lymphocyte lines, is produced by monocytic rather than lymphocytic leukocytes, and has subsequently been termed interleukin 1 (IL- 1)(2). More recently, it has become evident that IL-1 activities can be produced by virtually every nucleated cell type and, in addition, IL-1 has been reported to have stimulatory effects on the growth and differentiation of numerous cell types. In this review, Joost Oppenheim and his colleagues discuss the biochemical characteristics, gene cloning, cell sources, biological properties and actions of IL-1, and give reasons why this pleitotropic, nonspecific hormone-like cytokine is of considerable concern to immunologists.

gp63 in stable cationic liposomes confers sustained vaccine immunity to susceptible BALB/c mice infected with Leishmania donovani

Visceral leishmaniasis is deadly if not treated, and development of a vaccine with long-term immunity remains a challenge. In this study, we showed that cationic distearoyl phosphatidylcholine (DSPC) liposomes, when used as vaccine adjuvant with the immunodominant 63-kDa glycoprotein (gp63) of Leishmania donovani promastigotes, induced significant protection against progressive visceral leishmaniasis in susceptible BALB/c mice. gp63 used without adjuvant elicited partial protection but in association with liposomes exhibited marked resistance in both the livers and spleens of the mice challenged 10 days after the last vaccination. The protective efficacy of liposomal gp63 vaccination was dose dependent, with 2.5 mug of protein showing optimal protection. The immunity conferred by this vaccine formulation was durable, as mice challenged 12 weeks after immunization were still protected, and the infection was controlled for at least 3 months postchallenge. Production of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) by splenic T cells, and of serum immunoglobulin G1 (IgG1) and IgG2a following immunization, suggested that a mixed Th1/Th2 response had been induced following immunization. However, control of disease progression and parasitic burden in mice vaccinated with gp63 in cationic DSPC liposomes was associated with enhancement of antigen-specific IFN-gamma and downregulation of IL-4, demonstrating a Th1 bias. Long-term immunity elicited by this vaccine corresponded to, in addition to the presence of antigen-specific Th1, CD8+ T-cell responses. Our results demonstrated that stable cationic liposomes containing gp63 acted as a potent adjuvant for protein antigen to induce long-term protection against L. donovani that represents an alternative to DNA vaccination.

INFLUENCE OF PHOSPHOLIPID COMPOSITION ON THE ADJUVANTICITY AND PROTECTIVE EFFICACY OF LIPOSOME-ENCAPSULATED LEISHMANIA DONOVANI ANTIGENS

In this study, we evaluate the effect of phospholipid on the adjuvanicity and protective efficacy of liposome vaccine carriers against visceral leishmaniasis (VL) in a hamster model. Liposomes prepared with distearyol derivative of L-alpha-phosphatidyl choline (DSPC) having liquid crystalline transition temperature (Tc) 54 C were as efficient as dipalmitoyl (DPPC) (Tc 41 C) and dimyristoyl (DMPC) (Tc 23 C) derivatives in their ability to entrap Leishmania donovani membrane antigens (LAg) and to potentiate strong antigen-specific antibody responses. However, whereas LAg in DPPC and DMPC liposomes stimulated inconsistent delayed type hypersensitivity (DTH) responses, strong DTH was observed with LAg in DSPC liposomes. The heightened adjuvant activity of DSPC liposomes corresponded with 95% protection, with almost no protectivity with LAg in DPPC and DMPC liposomes, 4 mo after challenge with L. donovani. These data demonstrate the superiority of DSPC liposomes for formulation of L. donovani vaccine. In addition, they demonstrate a correlation of humoral and cell-mediated immunity with protection against VL in hamsters.

Association of class I HLA antigens with the clinical manifestations of Turkish patients with Behçet's disease

Genetic factors appear to be important in the pathogenesis of Behçet's disease. Although it is known to be strongly associated with HLA-B 51, the association of HLA class I antigens with specific clinical findings of the disease has not been studied extensively and the few studies are conflicting. The aim of this study was to investigate the association of HLA class I alleles with the manifestations of Behçet's disease in Turkish patients. Eighty-five patients with Behçet's disease were typed for HLA-A, B, and C antigens with the serologic, standard microlymphocytotoxicity technique. Possible associations of the HLA complex with clinical findings of Behçet's disease were examined. Statistically significant findings are as follows (P < 0.05): increased HLA-B 51 and decreased HLA-B35 frequency in patients with thrombophlebitis, increased HLA-A29 and decreased HLA-Bw6 frequency in patients with ocular involvement, decreased HLA-Cw2 frequency in patients with erythema nodosum, and decreased HLA-Cw 7 frequency in patients with genital ulceration. Of particular note, the results of this study suggest that the presence of HLA-B 51 and the absence of HLA-B35 can be regarded as laboratory risk factors of venous thrombosis in patients with Behçet's disease.

Intracellular processing of liposome-encapsulated antigens by macrophages depends upon the antigen

Two proteins, a recombinant malaria protein (R32NS1) and conalbumin, were encapsulated in separate liposomes. The mechanisms of presentation of unencapsulated and liposome-encapsulated R32NS1 and conalbumin to antigen-specific T-cell clones were investigated in in vitro antigen presentation assays using murine bone marrow-derived macrophages (BMs) as antigen-presenting cells. A much lower concentration of liposomal antigen than of unencapsulated antigen was required for T-cell proliferation. Liposome-encapsulated conalbumin required intracellular processing by BMs for antigen-specific T-cell proliferation, as determined by inhibition with chloroquine, NH4Cl, leupeptin, brefeldin A, monensin, antimycin A, NaF, and cycloheximide and by treatment of BMs with glutaraldehyde. Liposome-encapsulated conalbumin therefore follows the classical intracellular antigen processing pathway described for protein antigens. Similarly, unencapsulated conalbumin also required intracellular processing for presentation to antigen-specific T cells. In contrast, both unencapsulated R32NS1 and liposome-encapsulated R32NS1 were presented to T cells by BMs without undergoing internalization and intracellular processing. These results suggest that the antigen itself is the major element that determines whether a requirement exists for intracellular processing of liposomal antigens by macrophages.

Delivery of protein antigen to the major histocompatibility complex class I-restricted antigen presentation pathway

Major histocompatibility complex (MHC) class I-restricted antigen presentation normally requires a protein antigen to be synthesized in the cytosol of the antigen presenting cell (APC). Exogenous protein antigen could gain access to the class I presentation pathway if the protein is introduced into the cytosolic compartment of the APC. Approaches which release the protein antigen from endocytic vesicles have been employed to deliver protein antigen for the recognition by class I-restricted cytotoxic T lymphocytes (CTL). These include osmotic shock, electroporation, cationic and pH-sensitive liposomes. An alternative approach is to deliver a gene that encodes the protein antigen. In this case, the APC is transfected with a gene which synthesizes the "exogenous protein" in the cytosol. Delivery of protein antigen targeted for CTL induction in vivo follows a different strategy and generally requires an antigen carrier of lipidic/membranous nature, such as liposomes, immunostimulating complexes, and/or lipid conjugates. Macrophages that are responsible for scavenging the antigen play an important role in CTL induction. An optimal CTL inductive vaccine must contain other immuno-modulatory activities in addition to its activity in delivering antigen to the class I pathway. Attempts to attenuate viral infection and to improve anti-tumor immunity have been successful by delivering the exogenous antigen entrapped in liposomes. These animal model studies should be of great value in the development of potential vaccine formulation.

The costimulatory and differentiating activity of soluble class I MHC antigens for an autologous thymocyte population

Combined cultivation of macrophages with syngeneic thymocytes resulted in accumulation of soluble H-2Kk antigens in culture medium. Incubation of intact autologous thymocytes with these soluble class I MHC molecules was shown to induce functional maturation of thymocytes assayed in local graft-vs-host reaction. Similar thymocyte costimulating activity was detected for the papain-solubilized purified H-2Kk antigens. Soluble class I antigens were shown to costimulate IL2 production by thymocytes in response to submitogenic doses of exogenous IL2 and to increase PHA-induced thymocyte proliferation. Soluble class I molecules were shown to increase the level of expression of function-associated membrane antigens, H-2Kk, CD8 and CD4, and to trigger thymocyte differentiation. The expression of I-Ak antigens remained invariable. It was also shown that soluble autologous class I molecules may function as direct amplifiers of thymocyte proliferation in autologous, but not allogeneic, mixed leukocyte reactions. It is concluded that soluble MHC class I molecules are capable of triggering functional and phenotype differentiation of syngeneic thymocytes and acting as restricted coaccessory molecules when thymocyte activation is induced by a submitogenic dose of different stimuli.

Effect of a lipopeptidic formulation on macrophage activation and peptide presentation to T cells

We studied a 45-69 lipopeptide obtained by N-terminal modification with a N epsilon-palmitoyl lysine residue of the 45-69 peptide derived from the nef protein of HIV. T cells from animals immunized intraperitoneally with 45-69 lipopeptide proliferated in vitro in the presence of 45-69 peptide while no response was obtained after intraperitoneal immunization with 45-69 peptide. The efficiency of the 45-69 lipopeptide is supported by the covalent association to the N epsilon-palmitoyl lysine moiety. The immunogenicity of the 45-69 lipopeptide or of the unmodified peptide is dependent on the route of immunization but is not related to a mitogenic effect on cells or to an increase of the peptide antigenicity. Moreover, only 45-69 lipopeptide induces the secretion of cytokines such as IL-1, IL-6 and TNF-alpha by peritoneal macrophages. Finally, the use of 45-69 lipopeptide permits the activation of highly purified T cells without the addition of antigen-presenting cells. These results have implications for the formulation of synthetic vaccines.

Induction of cytolytic and antibody responses using Plasmodium falciparum repeatless circumsporozoite protein encapsulated in liposomes

Plasmodium circumsporozoite (CS) protein-induced antibody and T-cell responses are considered to be important in protective immunity. Since the key repeat determinant of the CS protein may actually restrict the recognition of other potential T- and B-cell sites, a modified Plasmodium falciparum CS protein lacking the central repeat region, RLF, was expressed in Escherichia coli. On purification, RLF was encapsulated into liposomes [L(RLF)] and used for the in vivo induction of cytolytic T lymphocytes (CTL) and antibodies. Immunization of B10.Br (H-2k) mice with L(RLF), but not with RLF, induced CD8+ CTL specific for the P. falciparum CS protein CTL epitope, amino acid residues 368-390. Anti-L(RLF) serum reacted with antigens on intact sporozoites and inhibited sporozoite invasion of hepatoma cells. Antibody specificity studies in New Zealand White rabbits revealed new B-cell sites localized in amino acid residues 84-94, 91-99, 97-106 and 367-375. Although the mechanisms by which liposomes enhance cellular and humoral immune responses remain unknown, liposome-formulated vaccines have been well tolerated in humans; hence, their use in vaccines, when efficacy depends on antibody and CTL responses, may be broadly applicable.

Plasmodium berghei-specific T cells respond to non-processed sporozoites presented by B cells

The mechanism of malaria protective immunity induced by immunization with radiation-attenuated Plasmodium sporozoites (SPZ) is only partially understood. For example, B and T cell responses specific for the circumsporozoite (CS) protein, a 46 kDa SPZ surface protein, have been characterized; however, events leading to SPZ-specific T cell activation, i.e., processing and presentation of SPZ by antigen-presenting cells have not been investigated. In the present study we describe the in vitro analysis of requirements for accessory cell function in the presentation of SPZ to SPZ-immune T cells. The results establish that SPZ-induced proliferative T cells are reactive to non-processed SPZ presented by activated B cells and, thus, imply that the non-processed form of the SPZ-associated CS protein restricts the induction of the potential CS protein T cell repertoire.

Specific and effective T-cell recognition of cells transfected with a truncated human mucin cDNA

Epithelial cell mucin has been characterized as a tumor-specific antigen in patients with pancreatic and breast cancer. Mucins are high molecular weight glycoproteins consisting of a heavily glycosylated tandemly repeating 20-amino acid sequence. Aberrant glycosylation of mucins on carcinomatous epithelial cells leads to the exposure of novel core epitopes that are recognized by cytotoxic T lymphocytes (CTLs). We previously reported the establishment of mucin-specific CTL clones that recognize mucin expressed on the surface of EBV-immortalized B cells transfected with the mucin cDNA (MUC1). This recognition was characterized as major histocompatibility complex (MHC)-unrestricted, because of the multivalent nature of mucin. The transfectants had to be incubated with an inhibitor of O-linked glycosylation, phenyl-N-acetyl-alpha-galactosaminide (phenyl-GalNAc) in order to unmask the tandem repeat core epitope recognized by CTLs. In the present study, we examined whether mucin molecules with fewer tandem repeats are capable of MHC-unrestricted recognition by mucin-specific CTL clones. A mucin cDNA expression vector expressing a "truncated" mucin molecule that contains only two tandem repeats was constructed. We found that mucin-specific CTL clones recognize the "truncated" mucin on allogeneic target cells, showing that recognition in this case was MHC-unrestricted as well. In addition, CTL clones lysed "truncated" mucin transfectants significantly better than full-length mucin transfectants treated with phenyl-GalNAc, and controls. The "truncated" construct may represent an effective means of immunizing patients with breast and pancreatic cancer, enabling them to mount a strong and efficient immune response against mucin-bearing tumor cells.

Antigen-specific, MHC-unrestricted T cells

The published record suggests that in the majority of cases the antigen is recognized by the T cell receptor (TCR) as a complex of a foreign antigen and amino acid residues contributed by the major histocompatibility complex (MHC) antigens, and the antigen-specific, MHC-restricted effector function is an unambiguous result of this process. Alternatively, the T cell receptor may recognize a particular conformational form of the antigen which is dictated by the allelic differences in the MHC, resulting also in MHC-restricted recognition. When, however, a T cell which phenotypically fulfills all the requirements necessary to perform antigen specific, MHC-restricted function, shows a lack of MHC restriction, there are two possible explanations: 1) In addition to the MHC-restricted, antigen-specific T cell receptor the cell expresses, or has newly acquired the expression of another, MHC-unrestricted (NK-like) receptor, or 2) The specific antigen recognized by the T cell receptor, is able to bind to the receptor and activate the T cell without being presented by the MHC molecule. While the first possibility has been extensively described in the literature as well as other articles in this issue, the second possibility has not been dealt with to the same extent and is the primary focus of this review.

Liposomes enhance the immunogenicity of reconstituted influenza virus A/PR/8 envelopes and the formation of protective antibody by influenza virus A/Sichuan/87 (H3N2) surface antigen

Reconstituted influenza virus (A/PR/8 strain) envelopes (RIVE) and influenza virus (A/Sichuan/87 (H3N2) strain) surface antigens were entrapped in dehydration-rehydration vesicles (DRV liposomes) composed of egg phosphatidylcholine (PC) or distearoyl phosphatidylcholine (DSPC DRV) and equimolar (32 mumol) cholesterol. Entrapment values for RIVE were 31.2 (PC) and 29.4% (DSPC DRV) of the material used. Corresponding entrapment values for the A/Sichuan/87 strain antigens were 40.7 and 39.3%. Balb/c mice injected intramuscularly with PC or DSPC DRV liposomes containing 0.1 and 1.0 microgram RIVE exhibited primary (higher dose only) and secondary responses (IgG1) which were significantly higher than those obtained in mice injected with identical amounts of non-entrapped RIVE. Significantly higher secondary responses were also observed for the IgG2a and IgG2b subclasses. In experiments designed to assess the effectiveness of DRV liposomes as a carrier of influenza virus antigens in a potential vaccine, hamsters were immunized intramuscularly with 0.1, 0.5 and 5.0 micrograms of free or liposome-entrapped influenza A/Sichuan/87 surface antigens. Results showed increased haemagglutination inhibition (HI) antibody levels in terms of both primary (0.5 and 5.0 micrograms doses) and secondary (all doses) responses in the sera of animals treated with the liposomal formulations. DSPC compared with PC DRV exhibited greater adjuvanticity when the lower doses of antigens were used.

Comparison of class I- and II-restricted T cell recognition of the identical peptide

There is structural and functional evidence that both class I- and II-restricted T cells recognize short processed peptides bound to MHC molecules. Although the structural conformation of bound peptides remains unknown, no evidence of distinct structural motifs of class I- or class II-restricted peptides has been described. Conversely, two algorithms proposed to predict T cell epitopes, and based on primary amino acid sequence or tertiary structure, are both compatible with many observed class I- and class II-restricted peptides. We previously identified eight class I-restricted peptides which were also recognized by class II-restricted T cells. Based on functional and direct binding studies, additional examples of peptides with both class I and II restrictions have been identified. In this study, we have directly compared the fine specificity of T cell recognition of a single epitope in a single mouse strain in the context of both class I- and class II-restricted responses. Based on a panel of analogue peptides with amino acid substitutions and peptides of various lengths, we observed several striking similarities in the recognition patterns of both class I- and class II-restricted T cells. In addition, some characteristics of recognition were different in the two systems indicating that the recognition processes were similar but not identical.

Liposomes as carriers of antigens and adjuvants

Liposomes have been widely used as carriers of protein or peptide antigens. Antigenic materials can be attached to the outer surface, encapsulated within the internal aqueous spaces, or reconstituted within the lipid bilayers of the liposomes. The natural tendency of liposomes to interact with macrophages has served as the primary rationale for utilizing liposomes as carriers of antigens. Liposomes also serve as carriers of a variety of adjuvants and mediators, including lipid A, muramyl dipeptide and its derivatives, interleukin-1, and interleukin-2. Research utilizing in vitro cell culture models has demonstrated that liposomes containing both appropriate antigens and major histocompatibility gene complex molecules can induce antigen-specific genetically restricted cytotoxic T lymphocytes. Liposomes induce immune reactions through classical interactions with antigen presenting cells. However, modelling experiments have also demonstrated that liposomes can even substitute for antigen presenting cells, and cell-free genetically restricted and nonrestricted presentation of antigens by liposomes to helper T lymphocytes has been demonstrated. Liposomes are successful for inducing potent immunity in vivo and they are now being employed in numerous immunization procedures and as vehicles for candidate vaccines.

Induction of in vitro and in vivo anti-tumor responses by sensitization of mice with liposomes containing a crude butanol extract of leukemia cells and transferred inter-membranously with cell-surface proteins

Generation of cytotoxic T lymphocytes (CTL) in vitro and tumor-rejection responses by sensitization of semi-syngeneic mice with tumor-antigen-reconstituted liposomes were investigated. Liposomes were prepared from a crude butanol extract (CBE) of BALBRVD leukemia cells and egg phosphatidylcholine (PC): 1,2-dimyristoylamido-1,2-deoxyphosphatidylcholine (DDPC) (3:2) or dimyristoylphosphatidylcholine (DMPC):DDPC (1:4). Inter-membrane protein transfer (IMPT) liposomes were prepared by incubating BALBRVD cells with DMPC:DDPC (1:4) liposomes. Sensitization of male CB6F1 mice with CBE or IMPT liposomes induced a level of cytotoxicity similar to that on sensitization with mitomycin-C(MMC)-treated BALBRVD against BALBRVD target cells after in vitro sensitization with the tumor cells. Sensitization with CBE alone resulted in only marginal cytotoxicity. The cytotoxic effector cells induced by either mode of sensitization were CD8+ T-cells whose recognition was Kd-restricted. No difference in specificity was observed with the different modes of sensitization. Two in vivo immunizations with CBE or with CBE liposomes at a dose of 25 micrograms of protein (equivalent to 2.5 x 10(7) cells) cause moderate inhibition of BALBRVD tumor growth in male CB6F1 mice and immunization with IMPT liposomes at a dose of 1 microgram of protein result in efficient protection.

Parameters affecting the immunogenicity of a liposome-associated synthetic hexapeptide antigen

The effect of liposome association on the immunogenicity of the hexapeptide IRGERA was investigated. When administered in the absence of a carrier and adjuvant this peptide, which corresponds to a linear epitope located at the C-terminus of histone H3, was not immunogenic. When mice were immunized with the peptide covalently linked to the surface of small unilamellar vesicles containing monophosphoryl lipid A as adjuvant, a relatively long-lasting response with memory cell induction was observed. The anti-peptide antibodies raised in this way reacted with the cognate sequence in the native histone. In contrast, coupling of the peptide to the surface of large vesicles yielded both an IgM and IgG response of short duration whereas encapsulation of the free peptide in large vesicles was ineffective. These results indicate that with short synthetic peptides, liposomes provide a substitute for a carrier protein. However, an adjuvant has to be incorporated in the vesicles in order to obtain an efficient immune response. Such an approach may be useful for designing synthetic vaccines.

Elimination of spleen and of lymph node macrophages and its difference in the effect on the immune response to particulate antigens

To study the role of macrophages in the in situ immune response to particulate antigens in spleen and popliteal lymph nodes (PLN), mice were injected with dichloromethylene diphosphonate (Cl2MDP)-containing liposomes to eliminate macrophages, followed by immunization with trinitrophenylated sheep red blood cells (TNP-SRBC). Depletion of macrophages in the spleen caused a strong decrease in the number of antibody-forming cells (AFC), which develop after intravenous (i.v.) injection of the antigen. These results strongly suggested the involvement of splenic macrophages in the processing of TNP-SRBC. In particular, the populations of marginal zone macrophages may be involved in the inductive phase of an antibody response to particulate antigens. These macrophages are strategically positioned at the end of the white pulp capillaries in the marginal zone of the spleen and they have their cell processes between the marginal zone-B cells. Elimination of macrophages in PLN had no effect on the number of AFC, which develop after subcutaneous (s.c.) injection of the antigen in the hind footpads. This indicates that the macrophages are not essential for the induction of a local immune response to the particulate antigen TNP-SRBC. After depletion of lymph node macrophages, the number of AFC developing in the spleen after s.c. footpad injection of the antigen increased and the anti-TNP serum titers were elevated. This may well be caused by the fact that more of the antigen reaches the circulation and subsequently stimulates the spleen.

Characterization of agretopes and epitopes involved in the presentation of beef insulin to T cells

Beef insulin-specific I-Ad-restricted T cell hybridomas were derived from the fusion of antigen-primed (BALB/c X B6)F1 T cells with BW5147 thymoma. Specificity analysis revealed that the A-chain loop region is involved in antigen recognition. Hybridoma A20.2.15 is specific for beef insulin and cross-reacted with sheep insulin, but not with pork insulin. Using synthetic peptides we showed that the A-chain loop containing peptide A1-A14 jointed to the B7-B15 peptide by a disulfide bond can activate this hybridoma. Fragments generated by enzyme digest further suggest that the peptide recognized on beef insulin appears to involve A-chain loop residues A5-A12 and B-chain residues B7-B13 that are linked by the A7-B7 disulfide bridge. We found that beef insulin needs to be processed prior to T cell activation. Glutaraldehyde fixation and chloroquine treatment of presenting cells abolished their capacity to present insulin. Beef insulin denatured by pH changes cannot activate, thus suggesting that simple denaturation is not sufficient for presentation by antigen presenting cells. Finally, the agretope on beef insulin is comprised of two functional regions B7-B13 on the B chain and the A-chain loop in the A-chain, while residues A8 and A10 are probably involved in interaction with the T cell receptor.

Presentation of Salmonella antigens by peritoneal cells of normal and Salmonella-infected mice

A comparison of the ability of normal peritoneal cells (PC) and those harvested from mice 1-3 days after intraperitoneal immunization with live Salmonella enteritidis 11RX (11RX) to present antigen to 11RX-primed T cells was made using formalin-killed 11RX and a soluble 11RX antigen extract as antigens. Unfractionated PC and the adherent and non-adherent PC populations were analysed separately and the effects of the lysosomal function-impairing drug chloroquine and the fixative paraformaldehyde, used before or after antigen-pulsing, were also determined. The results presented indicate that immunization with live 11RX did not induce any detectable modulation of APC function which could account for the ability of live 11RX to induce cell-mediated immune responses involving Lyt 2+ T cells.

T cells specific for alpha-beta interface regions of hemoglobin recognize the isolated subunit but not the tetramer and indicate presentation without processing

Processing of a protein antigen into fragments is believed to be a prerequisite for its presentation by the antigen-presenting cell to the T cell. This model would predict that, in oligomeric proteins, T cells prepared with specificity for regions that are buried within subunit association surfaces should recognize the respective regions in vitro equally well on the isolated subunit or on the oligomer. Three hemoglobin (Hb) alpha-chain synthetic peptides, corresponding to areas that are situated either completely [alpha-(31-45)] or partially [alpha-(41-45) and alpha-(81-95)] within the interface between the alpha and beta subunits of Hb, and a fourth peptide representing a completely exposed area in tetrameric Hb were used as immunogens in SJL/J (H-2s) mice. Peptide-primed T cells were passaged in vitro with the respective peptide to obtain peptide-specific T-lymphocyte lines. T-cell clones were isolated from these lines by limiting dilution. T-cell lines and clones that were specific for buried regions in the subunit association surfaces recognized the free peptide and the isolated subunit but not the Hb tetramer. On the other hand, T cells with specificity against regions that are not involved in subunit interaction and are completely exposed in the tetramer recognized the peptide, the isolated subunit, and the oligomeric protein equally well. The responses of the T-cell lines and clones were major histocompatibility complex-restricted. Since the same x-irradiated antigen-presenting cells were employed, the results could not be attributed to differences or defects in Hb processing. The findings indicate that in vitro the native (unprocessed and undissociated) oligomeric protein was the trigger of major histocompatibility complex-restricted T-cell responses.

Presentation of antigen to T lymphocytes by non-immune B-cell hybridoma clones: evidence for specific and non-specific presentation

Non-immune SJL (H-2s) spleen cells were fused with non-secreting, non-antigen presenting (H-2d) Balb/c 653-myeloma cells and the hybridomas were cloned by two limiting dilutions. The resulting hybrid B-cell clones were tested for their antigen presentation capability to SJL T-cell lines that were specific for either lysozyme or myoglobin. In proliferative assays, 53% of the antigen presenting B-cell clones presented both myoglobin and lysozyme (general presenters) while the other 47% presented specifically either myoglobin or lysozyme (specific presenters). The ability to selectively present either myoglobin or lysozyme indicates that antigen presentation at the clonal level can be specific or non-specific depending on the particular B-cell clone.

Conformation-dependent recognition of a protein by T cells requires presentation without processing

Presentation of a protein antigen to T cells is believed to follow its intracellular breakdown by the antigen-presenting cell, with the fragments constituting the trigger of immune recognition. It should then be expected that T-cell recognition of protein antigens in vitro will be independent of protein conformation. Three T-cell lines were made by passage in vitro with native lysozyme of T cells from two mouse strains (B10.BR and DBA/1) that had been primed with the same protein. These cell lines responded well to native lysozyme and very poorly to unfolded (S-sulphopropyl) lysozyme. The response of the T-cell lines to the antigen was major histocompatibility complex (MHC)-restricted. A line from B10.BR was selected for further studies. This line responded to the three surface-simulation synthetic sites of lysozyme (representing the discontinuous antigenic, i.e. antibody binding, sites) and analogues that were extended to a uniform size by a nonsense sequence. T-cell clones prepared from this line were specific to native lysozyme and did not respond to the unfolded derivative. Furthermore, several of these clones showed specificity to a given surface-simulation synthetic site. The exquisite dependency of the recognition by the clones on the conformation of the protein antigen and their ability to recognize the surface-simulation synthetic sites indicate that the native (unprocessed) protein was the trigger of MHC-restricted T-cell recognition.

T-cell recognition and antigen presentation of myoglobin. Protein recognition by site-specific T-cell clones is influenced by amino acid substitutions outside the site

Six T-cell clones from SJL mice were prepared from T-cell lines that were obtained by passage with synthetic myoglobin (Mb) peptide 107-120. In addition, a T-cell clone, specific to this region of Mb, was isolated from a Mb-passaged T-cell culture. The proliferative responses of these clones to Mb variants from 14 different species were studied. It was found, as expected, that amino acid replacements within the site affected its recognition by the T-cell clones. In addition to these effects, the T-cell recognition site, like the sites recognized by antibodies, was also influenced by substitutions of residues that are close to site residues in three-dimensional structure but are otherwise distant in sequence. This is noteworthy in view of the fact that six of the clones were selected with a free peptide, and thus the environmental residues are clearly not part of the 'contact' residues of the site. These findings are discussed in relation to the presentation of the antigen and are interpreted as indicating that Mb is presented in its intact form to the T-cells in vitro.

Immunoadjuvant action of liposomes: comparison with other adjuvants

Dehydration-rehydration vesicles (DRV liposomes) composed of equimolar phospholipid and cholesterol and containing bovine serum albumin (BSA) were used together with free BSA to immunize Balb/C mice. Primary and secondary immune responses (IgG1) to the liposomal antigen, as measured by ELISA in mouse sera, were similar for egg phosphatidylcholine (PC) and distearoyl phosphatidylcholine (DSPC) DRV, and much greater than those elicited by free BSA. The adjuvanticity of PC DRV was compared with that of aluminium salts (alum), complete Freund's adjuvant (CFA) and N-acetyl muramyl-L-threonyl-D-isoglutamine ([Thr1]MDP), the latter used as such or in a liposome form co-entrapped with the antigen. DRV (with or without co-entrapped [Thr1]MDP), and alum were equally strong in producing primary and secondary immune responses (IgG1) to BSA. Such responses were significantly higher than those achieved with CFA and [Thr1]MDP alone. The implications of these results for the potential role of liposomes as immunological adjuvants in vaccines are discussed.

Murine macrophage cell line AP284 presents antigen to cloned MT4+, Lyt-2- T cells in vitro and in vivo

A murine macrophage cell line AP284 that appeared to be mature in phenotype was isolated. After repeated cloning, the cell line expressed the markers Mac-1, Mac-2, Mac-3, 2.4G2, F4/80 as well as Ia antigens. Moreover, it was positive for the enzymes nonspecific esterase and acid phosphatase, negative for alkaline phosphatase and was able to phagocytize latex beads. We studied whether this cell line was able to present antigen to cloned MT4+, Lyt-2- T cells specific for methylated bovine serum albumin (mBSA) or ovalbumin (OVA). The in vitro proliferative response of the cloned T cells specific for mBSA or OVA was found to be effectively supported by AP284. This proliferation could be blocked by monoclonal antibodies against Ia determinants. AP284 also effectively presented antigen in vivo as was shown in a foot swelling assay measuring delayed type hypersensitivity (DTH) to mBSA caused by specific cloned T cells with the helper phenotype. This offers a unique model system for studying the process of antigen presentation in which both the antigen presenting cells and the T cells are monoclonal.

Antigen processing for presentation to T lymphocytes: function, mechanisms, and implications for the T-cell repertoire

Antigen processing encompasses the metabolic events that a protein antigen must undergo in or on the antigen-presenting cell before it can be recognized by the T lymphocyte. It appears that a primary goal of these events is to unfold the protein to expose residues that are buried in the native conformation, which is designed to be soluble in water. The APC usually accomplishes this task by proteolytic cleavage of the protein, but we have found that artificial unfolding without proteolysis is sufficient. The purpose of unfolding may be to allow different faces of the antigenic site to bind simultaneously to the T-cell receptor and the MHC molecule on the APC, or to interact with other structures on the membrane of the APC. This requirement for unfolding appears to apply to everything from small peptides to large multimeric proteins. We have found that the way the antigen is processed and the structure of the fragments produced can greatly affect the availability of antigenic sites. For instance, some antigenic sites are not recognized when the native protein is used as immunogen, despite the fact that immunization with a small peptide corresponding to that site reveals both the ability of the site to bind to MHC molecules of the animal in question and the presence of a T-cell repertoire specific for that site. The antigenic site is not destroyed by processing, since it can be presented by the same F1 APC to T cells of another MHC type. Similarly, cross-reactivity between homologous epitopes of related proteins may occur at the peptide level even though the native proteins do not crossreact for the same T-cell clone. Since these events occur with monoclonal T cells, they cannot be due to suppressor cells specific for other sites on the native molecule. The best explanation is that the products of natural processing of the protein are larger than the peptides corresponding to the minimal antigenic sites, and contain hindering structures that interfere with binding to some MHC molecules and not others, or to some T-cell receptors and not others. Thus, antigen processing is a third factor that can lead to apparent Ir gene defects - in addition to MHC specificity and holes in the T-cell repertoire - and can significantly influence which antigenic sites are immunodominant.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen presentation by liposomes as model system for T-B cell interaction

Using the earlier established liposome system for antigen presentation, in which liposomes bearing major histocompatibility complex (MHC)-class II molecules inserted into and protein antigen covalently linked to the membrane were found to be sufficient for an antigen-specific and MHC-restricted activation of T cells, the minimal requirements for T-B cell interaction were investigated. Liposomes carrying MHC class II molecules and antigen-specific monoclonal antibodies were constructed and tested for their ability to present soluble antigen to T cells. With the antigens lactate dehydrogenase B and pigeon cytochrome c, a specific stimulation of T cell clones and hybridomas could be obtained. These results demonstrate the possibility of a direct involvement of the immunoglobulins on the B cell surface in their interaction with T cells.

Conformation-dependent recognition of a protein by T-lymphocytes: apomyoglobin-specific T-cell clone recognizes conformational changes between apomyoglobin and myoglobin

A T-cell clone specific to apomyoglobin was generated. It was prepared from a T-cell culture obtained by in vitro driving of lymph node cells with apomyoglobin from SJL mice that have been primed in vivo with apomyoglobin. In proliferative assays, the T-cell clone responded to apomyoglobin but did not recognize native myoglobin or any of the synthetic peptides corresponding to the six T sites of myoglobin. The demonstration that a T-cell clone can be isolated, whose specificity is directed entirely to apomyoglobin and not to its counterpart myoglobin, with an identical amino acid composition, indicates the importance of the three-dimensional structure in the presentation of the protein to T cells.

HLA DPw1 class II molecules on human T cells

Human T cells express HLA class II antigens when activated by mitogens, alloantigens, or nominal antigens such as influenza virus. However, little is known about why they are expressed and the extent to which subsets of class II molecules (DR, DQ, and DP) are expressed. From studies with allocytotoxic antisera it is clear that DR and DQ molecules are expressed by T cells; cell surface expression of DP is more ambiguous because cellular typing methodologies are required. Alloreactive T-cell clones, specific for DPw1-associated antigens, were derived by limiting dilution in the presence of DPw1-positive stimulator PBLs and IL-2 and screened on panels of DPw1-positive and DPw1-negative PBL's in proliferation assays. Clones that recognized DPw1-associated determinants were then assayed for responses using as stimulators, irradiated T-cell clones derived from a DPw1-positive donor. Of seven DPw1-specific clones, one (TLC 56.26) was highly responsive to the alloantigens expressed on the stimulator T-cell panel. Six such clones gave a range of lower responses to T cells although capable of recognizing DP-associated determinants on PBL stimulators.

Differences between primed allogeneic T-cell responses and the primary mixed leucocyte reaction. Primed T cells become independent of the blocking effects of monoclonal antibodies against IL-1 beta and the CD5, CD11a (LFA-1), and CD11c (p 150,95) molecules

Recent investigations have demonstrated that the primary mixed lymphocyte reaction (MLR) is dependent on certain accessory molecules, e.g. CD4 and LFA-1. We have compared the requirements of the primary MLR and the responses of alloreactive, primed lymphocytes (PL) by inhibition studies using monoclonal antibodies (MoAb) directed against (i) adhesion molecules belonging to the CD11 cluster of leucocyte antigens (CD11a, LFA-1; CD11b, MAC1 = CR3; and CD11c, p 150,95); (ii) various T cell-related antigens (CD2, CD4, CD5 and CD8); and (iii) recombinant IL-1 beta. The CD5-, CD11a- and CD11c-reactive MoAb significantly inhibited the primary MLR (inhibition = 25%, P less than or equal to 0.01; 48%, P less than or equal to 0.01 and 13%, P less than or equal to 0.05, respectively) but these MoAb did not inhibit the primed lymphocyte reaction (PLR). The CD11b-reactive MoAb had no significant influence on either of the responses. CD2- and CD4- reactive MoAb significantly inhibited both primary MLR (greater than 80%, P less than or equal to 0.01) and to a lesser extent the PLR (40-65%, P less than or equal to 0.01). A MoAb reactive with IL-1 beta inhibited the primary MLR (38%, P less than 0.01) and the purified protein derivative (PPD) induced lymphocyte transformation response (42%, P less than or equal to 0.01) of peripheral blood mononuclear cells (PBMC), whereas primed allogeneic responses to PBMC and Epstein-Barr virus (EBV) cell lines were unaffected by this MoAb. In addition, preliminary data indicated that PL seemed neither to bind exogenous IL-1 (as opposed to CD4+ PBMC) nor to possess membrane-bound IL-1. The differences between 'virgin' and primed, allogeneic T-cell responses indicate that profound changes in the functional capability of the responding T-cell population take place during the bulk expansion. The results indicate that during repeated priming with alloantigen and bulk expansion, the proliferative response of T lymphocytes becomes independent of (i) the interaction with the CD11 adhesion molecule(s), (ii) the CD5 molecule, and (iii) the cytokine IL-1 beta.

Insulin-dependent diabetes mellitus induced in transgenic mice by ectopic expression of class II MHC and interferon-gamma

We have produced transgenic mouse strains harboring class II major histocompatibility complex or interferon-gamma genes linked to the human insulin promoter. These experiments were designed to investigate the consequences of the expression of immunological effector molecules by nonimmunological cells. In both of these studies we observed the disappearance from the pancreas of the insulin-producing beta cells coinciding with the development of insulin-dependent diabetes mellitus. Transgenic mice expressing both chains of the I-A gene showed progressive atrophy of the islets of Langerhans, whereas mice expressing interferon-gamma suffered an inflammatory destruction of the islets.

Ultrastructural localization of 2,4-dinitrophenyl groups in mouse epidermis following skin painting with 2,4-dinitrofluorobenzene and 2,4-dinitrothiocyanatebenzene: an immunoelectron microscopical study

The ultrastructural localization of 2,4-dinitrophenyl (DNP) groups in mouse epidermis after epicutaneous application of the contact sensitizer 2,4-dinitrofluorobenzene (DNFB) and the tolerogen 2,4-dinitrothiocyanatebenzene (DNTB) was investigated at varying times using immunoelectron microscopy with the protein A - gold technique. After application of DNFB, there was a homogenous cytoplasmic labeling of all epidermal cells. The intracellular localization of the DNP groups was not restricted to cytoplasmic organelles belonging to the endocytotic - lysosomal system. The numerous endocytotic organelles, Birbeck granules, and lysosomes of the Langerhans cells (LCs) typically observed after application of contact sensitizers also did not show an increased number of gold particles. Skin painting with DNTB resulted in a similar distribution and time-course of immunolabeling, but this compound did not induce cellular and the endocytotic activation of LCs as seen after DNFB application. These results demonstrate that contact sensitizers do not require specific cellular uptake and intracellular processing by the endocytotic - lysosomal compartment of the LCs before membrane presentation. However, a cellular and endocytotic activation of the LCs by haptens may be an important mechanism for T effector cell activation.

Primary activation of murine CD8 T cells via cross-linking of T3 cell surface structures: two signals regulate induction of interleukin 2 responsiveness

In the model system used here to study the minimal signal requirements for the activation of murine resting CD8 T cells, cross-linking of T cell receptor structures by antigen-presenting cells is substituted for by the use of anti-CD3 monoclonal antibodies immobilized in Sepharose beads. We show that cross-linking of CD3 structures, even in combination with CD8 structures, is necessary but insufficient to induce responsiveness to the growth-promoting effect of interleukin 2 (IL2), i.e. fails to induce expression of functional IL2 receptors. A macrophage cell line product termed IL2 receptor-inducing factor (RIF), but not IL1, IL3, IL4 or tumor necrosis factor, efficiently functions as costimulator. Once activated, growth of CD8 T cells is entirely driven by IL2. We conclude that two restriction points control the activation of resting CD8 T cells. While cross-linking of CD3 structures is essential as a first step, RIF is required as competence factor to induce IL2 responsiveness. We consider the possibility that the ability of antigen-presenting cells to produce RIF determines the immunogenicity of presented antigen towards antigen-reactive resting CD8 T cells.

Ultrastructural cytochemical visualization of chromium in the skin of sensitized guinea pigs

Using a modified sulfide silver method for electron microscopy, the intraepidermal and intracellular localization of epicutaneously applied potassium dichromate was investigated at varying times in sensitized and nonsensitized guinea pigs. The hapten penetrated rapidly into the epidermis. There was a homogeneous extra- and intracellular staining of the keratinocytes in the upper epidermis. The basal and suprabasal cells, by contrast, exhibited a predominant extracellular and plasma membrane localization of the silver grains. This membrane staining pattern was also observed in the Langerhans cells showing cellular and endocytotic activation in the sensitized animals. No specific cellular uptake of the hapten by the Langerhans cells was found. These results demonstrate that the epicutaneous application of chromate resulted in a characteristic intraepidermal distribution which may be related to the epidermal conversion of the hexavalent chromate to the immunogenic trivalent form. Moreover, the absent intracellular localization of the hapten in the activated Langerhans cells supports the notion that contact allergens can be presented to T cells without prior intracellular processing.

Impairment of immunogenicity by antigen presentation in liposomes made from dimyristoylphosphatidylethanolamine linked to the secretion of prostaglandins by macrophages

The induction of antibody response in syngeneic rats by the Gross virus cell surface antigen (GCSAa) was dependent on the presentation of GCSAa into liposomes made from distearoylphosphatidylcholine (DSPC). GCSAa liposomes made from dimyristoylphosphatidylethanolamine (DMPE) were nonimmunogenic, even when used as anamnestic immunogens. Spleen cells, from rats twice immunized with GCSAa-DSPC-liposomes and used to transfer the anti-GCSAa immune response into naive recipients after a tertiary immunostimulation in vitro in the presence of naive peritoneal exudate cells (PEC), responded to soluble GCSAa only after irradiation at 500 rds and to GCSAa-DMPE-liposomes only when indomethacin was added during the in vitro stimulation. The preincubation of these cells with empty DMPE liposomes or the addition of supernatant from PEC fed with DMPE liposomes abrogated the response to GCSAa-DSPC liposomes. Using a specific radioimmunoassay, prostaglandin E2 was demonstrated to be produced by PEC when fed with DMPE liposomes, and not when fed with DSPC liposomes. This prostaglandin E2 secretion by PEC induced by DMPE liposomes was inhibited by indomethacin.

Antigen-targeted liposome-encapsulated methotrexate specifically kills lymphocytes sensitized to the nonapeptide of myelin basic protein

Antigen targeting of liposome-encapsulated cytotoxic drugs to specific lymphocytes may be a useful approach for antigen-specific immunosuppressive treatment of autoimmune diseases in which a specific antigen is involved. The feasibility of utilizing this approach was investigated using experimental allergic encephalomyelitis as an animal model for an autoimmune response. The encephalitogenic determinant of myelin basic protein for the guinea pig is contained in residues 114-122, the so-called nonapeptide. We have acylated the nonapeptide at its N-terminal to anchor it in the lipid bilayer of liposomes containing the cytotoxic drug methotrexate. The nonapeptide on the surface of the liposomes then allows targeting of the liposomal methotrexate in vitro to anti-nonapeptide T lymphocytes obtained from guinea pigs with experimental allergic encephalomyelitis. Treatment with the nonapeptide-targeted liposomal methotrexate inhibited proliferation of anti-nonapeptide lymphocytes significantly more than that of control lymphocytes. These included non-sensitized lymphocytes, stimulated with phytohemagglutinin, or lymphocytes sensitized to different, unrelated proteins, the purified protein derivative of tuberculin and keyhole limpet hemocyanin, and stimulated with their specific antigens. Furthermore, nonapeptide-targeted liposomes had a greater cytotoxic effect on anti-nonapeptide T cells than untargeted liposomes. The results indicated that specific targeting to and killing of anti-nonapeptide cells was achieved, although improvements of the treatment are necessary before its use can be attempted in vivo.