IL-10 acts on the antigen-presenting cell to inhibit cytokine production by Th1 cells

Murine IL-10 (cytokine synthesis inhibitory factor) inhibits cytokine production by Th1 cell clones when they are activated under conditions requiring the presence of APC. By preincubating APC with IL-10, we demonstrate that IL-10 acts principally on APC to inhibit IFN-gamma production by Th1 clones. Moreover, IL-10 is not active when Th1 cells are stimulated with glutaraldehyde-fixed APC, which also indicates that its action involves regulation of APC function. Furthermore, IL-10 inhibits cytokine synthesis by Th1 cells stimulated with the super-antigen Staphylococcus enterotoxin B, which does not appear to require processing. Flow microfluorimetry purified splenic or peritoneal B cells and macrophages, and B cell and macrophage cell lines can present Ag to Th1 clones. However, IL-10 acts only on sorted macrophages and the macrophage cell line to suppress IFN-gamma production by Th1 clones. IL-10 does not show this effect when B cells are used as APC. In contrast, IL-10 does not impair the ability of APC to stimulate cytokine production by Th2 cells. IL-10 does not decrease IFN-gamma-induced I-Ad levels on a macrophage cell line. Inasmuch as IL-10 also inhibits IL-2-induced IFN-gamma production by Th1 cells in an Ag-free system requiring only the presence of accessory cells, these data suggest that IL-10 may inhibit macrophage accessory cell function which is independent of TCR-class II MHC interactions.     

Two distinct mechanisms account for the immune response (Ir) gene control of the T cell response to pigeon cytochrome c

Previous experiments have demonstrated that the immune response of MHC congenic mice to pigeon cytochrome c is under Ir gene control. Expression of I-E-encoded gene products influences both the magnitude and fine specificity of the Th cell response to pigeon cytochrome c and phylogenetic derivatives. Results of those experiments implicate both determinant selection and repertoire selection as mechanisms of Ir gene control in this system. In this report we have compared the TCR expressed in pigeon cytochrome c-reactive Th cells from B10.A(I-Ek), B10.A(5R) (I-Eb), and B10.S(9R) (I-Es) mice. The B10.A(5R) strain is a low responder to pigeon cytochrome c, but in response to moth cytochrome c this strain produces T cells which respond to pigeon or moth cytochrome c on B10.A APC. These cells are phenotypically identical to the predominant clonal phenotype seen in the B10.A response to pigeon cytochrome c. In this report, we show that the B10.A and B10.A(5R) pigeon cytochrome c-reactive T cells express essentially identical T cell receptors. These results, coupled with recent studies reporting a relatively low affinity for I-Eb molecules by pigeon cytochrome c peptides compared with moth cytochrome c peptides, strongly argue that the immune response defect in the B10.A(5R) strain is due to a defect in Ag presentation (determinant selection). In contrast, B10.A and B10.S(9R) strains are high responders to pigeon cytochrome c. Both strains produce T cell clones which are capable of responding to cytochrome c presented by either B10.A or B10.S(9R) APC in vitro. We show that, even in T cells with this MHC restriction degeneracy, the TCR expressed in the two strains are different. Because the APC of both strains can clearly present the cytochrome c Ag, we conclude that the differential expression of the TCR in the responses is due to a T cell repertoire selection difference in the two strains. Thus, for the response to one Ag in three MHC congenic strains, there exists evidence that both determinant selection and repertoire selection can be mechanisms of Ir gene control of an immune response.     

IL 1 induction by murine T cell clones: detection of an IL 1-inducing lymphokine

T cell activation is widely believed to depend on interleukin 1 (IL 1) provided by antigen (Ag)-presenting cells (APC). Because IL 1 is not a constitutive product of APC, we examined the features of its production during the interaction of murine T cell clones and APC. We observed that IL 1 was detectable in supernatants of most myoglobin-specific T cell clones grown with APC and Ag. Two of these T cell clones induced exceptionally high levels of IL 1 in their supernatants, and these same clones demonstrated the unusual restriction to I-Ek, which is a low responder type for sperm whale myoglobin. One of these clones was characterized additionally as to the mechanism of IL 1 induction. This clone rapidly stimulated IL 1 production in the APC population (detectable at 4 hr of co-culture) or in macrophages (M phi) or a M phi-like cell line. IL 1 induction was Ag dependent and H-2 restricted. Induction was radioresistant, both on the part of the T cell and of the IL 1 producer. The IL 1-induction process was attributable to a lymphokine produced by the T cell clone. This lymphokine was distinct from IFN-gamma, TNF and CSF-1 and may account for a principal mechanism of T----APC signalling. The induced IL 1 was the same in size, co-mitogenicity, and pyrogenicity as lipopolysaccharide-induced IL 1.     

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

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

Stimulation of human naive and memory T helper cells with bacterial superantigen. Naive CD4+45RA+ T cells require a costimulatory signal mediated through the LFA-1/ICAM-1 pathway.

The role of the accessory molecule ICAM-1 in activation of subpopulations of human T cells was examined using the bacterial superantigen staphylococcal enterotoxin A (SEA) as a MHC class II and TCR-dependent polyclonal T cell activator. Human T cells responded with different sensitivity to SEA when presented on mouse accessory cells expressing a human transfected MHC class II gene product. Mouse L cells cotransfected with both MHC class II (DR2A or DR7) and ICAM-1-stimulated T cells at 100-fold lower concentrations of SEA as compared to the single transfected cells. mAb reacting with the CD11a, CD18, or ICAM-1 molecules efficiently inhibited T cell activation with the cotransfected HLA-DR2A/ICAM-1 cell but did not influence T cell activation with the HLA-DR2A single transfected cell. Analysis of the ICAM-1 requirement on CD4+ memory (CD4+45RO+) and naive (CD4+45RA+) T cells revealed that CD4+45RA+ naive Th cells were hyporesponsive to SEA-induced activation with the HLA-DR2A single transfectant. However, cotransfection of ICAM-1 enabled these cells to respond to low doses of SEA implicating that they are more dependent on accessory molecules than the CD4+45RO+ cells. rICAM-1 immobilized on a plastic surface, was able to strongly costimulate SEA-induced T cell activation with the HLA-DR2A single transfectant, suggesting that costimulatory signals mediated to the T cells through LFA-1 can be delivered physically separated from the TCR signal. CD4+45RO+ memory and CD4+45RA+ naive Th cells apparently differ in their capacities to be activated by SEA bound to HLA-DR. Although the TCR molecule densities are similar in these two subsets, costimulation with ICAM-1 is required for activation of the CD4+45RA+, but not the CD4+45RO+ T cell subset at 1 to 10,000 ng/ml concentrations of SEA. This observation indicates different activation thresholds of naive and memory Th cells when triggering the TCR over a wide dose interval of superantigen.     

Class II MHC/peptide complexes are released from APC and are acquired by T cell responders during specific antigen recognition.

T cell expression of class II MHC/peptide complexes may be important for maintenance of peripheral self-tolerance, but mechanisms underlying the genesis of class II MHC glycoproteins on T cells are not well resolved. T cell APC (T-APC) used herein were transformed IL-2-dependent clones that constitutively synthesized class II MHC glycoproteins. When pulsed with myelin basic protein (MBP) and injected into Lewis rats, these T-APC reduced the severity of experimental autoimmune encephalomyelitis, whereas unpulsed T-APC were without activity. Normal MBP-reactive clones cultured without APC did not express class II MHC even when activated with mitogens and exposed to IFN-gamma. However, during a 4-h culture with T-APC or macrophage APC, recognition of MBP or mitogenic activation of responder T cells elicited high levels of I-A and I-E expression on responders. Acquisition of class II MHC glycoproteins by responders was resistant to the protein synthesis inhibitor cycloheximide, coincided with transfer of a PKH26 lipophilic dye from APC to responders, and resulted in the expression of syngeneic and allogeneic MHC glycoproteins on responders. Unlike rested I-A- T cell clones, rat thymic and splenic T cells expressed readily detectable levels of class II MHC glycoproteins. When preactivated with mitogens, naive T cells acquired APC-derived MHC class II molecules and other membrane-associated proteins when cultured with xenogeneic APC in the absence of Ag. In conclusion, this study provides evidence that APC donate membrane-bound peptide/MHC complexes to Ag-specific T cell responders by a mechanism associated with the induction of tolerance.     

Antigen-specific, MHC-restricted B cell activation by cell-free Th2 cell products. Synergy between antigen-specific helper factors and IL-4

Ag-specific and MHC-restricted Th clones of different Ag specificities and MHC haplotypes were tested for their ability to produce soluble factors capable of providing the signals required for B cell activation and IgG antibody production. Each of five Th clones tested generated significant helper activity in supernatants derived from coculture of the T cell clone with specific Ag and syngeneic APC. The same helper activity was detected in supernatants of clones stimulated with immobilized anti-CD3 antibody in the absence of Ag or APC. The secreted helper activity resembled the activity of the intact Th cells in that it was Ag-specific, carrier-hapten-linked and MHC-restricted. These T cell products functioned to activate only those B cells expressing MHC products which corresponded to the specificity of each Th clone. Thus, the specificity of the cell-free T cell product mimicked precisely that expressed by the intact Th cell and presumably mediated by the cell surface TcR. In addition to the apparent presence of specific helper factor in Th clone supernatants, a role for nonspecific lymphokines was also identified in these preparations. Although recombinant or purified IL-4 alone was not sufficient to stimulate hapten-primed B cells to secrete hapten-specific IgG antibodies, mAb specific for IL-4 blocked the induction of antibody secretion by Th cell supernatant. These results indicate that stimulation of B cells to produce hapten-specific IgG antibody requires at least two distinct signals: an Ag-specific T cell signal which is restricted by MHC products expressed on the B cells, and a nonspecific signal mediated at least in part by the lymphokine IL-4.     

The human antimurine xenogeneic cytotoxic response. I. Dependence on responder antigen-presenting cells

We have examined the role of the human responder APC in the generation of CTL responses to xenogeneic antigens. Of six xenogeneic responses evaluated, only the human antimurine response was dependent on human APC for CTL generation. APC requirements for the other five xenogeneic responses more closely resembled those observed in the generation of human or murine alloreactive CTL. Depletion studies identified a defective human CD4+ Th cell-murine stimulator cell interaction that could be bypassed by the addition of exogenous IL-2. The function of the responder APC involved in the human antimurine CTL response was inhibited by chloroquine, suggesting a requirement for Ag processing. Effective presentation of murine stimulator Ag by human APC was completely blocked by anti-human Ia mAb, indicating that the Ag is presented to Th cells via the human class II molecule. These results are consistent with an Ia-dependent recognition of processed murine Ag by human T cells and represents a model for investigating human T cell activation requirements, Th cell function, and MHC restriction.     

Human T cell clones present antigen

Two human T cells clones are described which react with influenza virus hemagglutinin type H3 and synthetic peptides of H3 when presented by PBMC APC. Both T cell clones also responded to peptide Ag in the absence of additional APC suggesting that T cells can simultaneously present and respond to Ag. T cell clones could only present peptide Ag and not an appropriate strain of inactivated whole influenza virus thus indicating an inability to process Ag conventionally. Peptide presentation by T cells was dose dependent, restricted by MHC class II Ag and was dependent on the number of Ag presenting T cells per culture. Experiments with nested peptides showed that the same epitope was recognized in the presence and absence of PBMC APC. No Ag or IL-2 from the propagation procedure was carried over into assays and two-color fluorescence-activated cell sorter analysis of each clone detected no contaminating cells with the phenotype of monocytes, macrophages or B cells; in each T cell clone, all cells expressing MHC class II Ag co-expressed CD3. These date therefore provide strong evidence that human T cell clones can simultaneously present and respond to appropriate forms of Ag.     

Antigen-specific T cells with monogamous or promiscuous restriction patterns are sensitive to different HLA-DR beta chain substitutions

The contributions of the amino acids at 13 polymorphic positions in the HLA-DR7 beta 1 chain to T cell recognition of two antigenic peptides of tetanus toxin (p2 and p30) were assessed using transfectants expressing mutant DR7 beta 1 chains as APC for six toxin-specific T cell clones with two different restriction patterns: monogamous (restricted by DR7 only) or promiscuous (restricted by DR7; DR1; DR2, Dw21; and DR4, Dw4). Each of the 13 substitutions significantly decreased or eliminated the ability of the DR7 molecule to present a peptide to one or more of the T cell clones, but none of the substitutions abolished recognition by all clones. Interestingly, substitutions at positions 4 and 25, which are predicted in the class II model to be located outside the peptide binding groove, decreased the ability of the DR7 molecule to present Ag to some clones but not to others. Each of the four clones specific for the p2 peptide and the two clones specific for peptide p30 had a different reactivity pattern to the panel of DR7 beta 1 mutants, indicating that the TCR of each clone has a different view of the p2/DR7 or p30/DR7 complex. These data emphasize the complexity of the interactions of multiple residues in DR7 beta 1 chains in Ag-specific T cell recognition.     

Epstein-Barr virus-transformed lymphoblastoid cell lines as antigen-presenting cells and "augmenting" cells for human CMV-specific Th clones

The ability of Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) to present human cytomegalovirus (HCMV) antigen to a panel of HCMV-specific T helper (Th) clones was evaluated. Among the seven Th clones studied, only one clone (SP-CN/T3-16) proliferated well to HCMV presented by both autologous mononuclear cells (MNC) and LCL, and one clone (SP-CN/T3-9) proliferated significantly better to HCMV presented by autologous LCL than by autologous MNC. The majority of the HCMV-specific Th clones tested (five out of seven) responded much better to HCMV presented by MNC than to HCMV presented by LCL. The mechanism(s) responsible for the inefficiency of LCL to present HCMV to certain clones was studied. Our results suggested that the defect of LCL is not due to insufficient interleukin 1 production, insufficient MHC class II molecule expression, nor an inhibitory mechanism or factor. In this report, we also demonstrate that by adding a minimum amount of LCL along with MNC as antigen-presenting cells (APC), one can restimulate and expand Th clones much more efficiently than by using MNC alone as APC.     

IL-1 is an autocrine growth factor for T cell clones

Activation of Th lymphocytes requires that Ag be presented on the surface of accessory cells displaying Ia Ag. A number of studies have concluded that the T cell also requires IL-1 from accessory cells. However, we recently reported that one murine T cell clone (D10.G4.1) produced its own IL-1-like activity after encountering APC (9). In this report, we demonstrate that 1) IL-1 production is a common property of murine T cell clones, 2) T cell IL-1 activity is blocked by anti-IL-1-alpha antiserum, 3) IL-1-alpha mRNA can be directly visualized in individual cloned T cells using in situ hybridization techniques, and 4) IL-1 appears to serve an autocrine role in the activation of T cell clones inasmuch as anti-IL-1-alpha antiserum blocks cell proliferation when the T cell is the only IL-1 source.     

Accessory cell function of Th2 clones

We have investigated the ability of T helper clones to serve as accessory cells and in the presence of mitogen activate freshly-isolated, splenic T cells. In this type of costimulatory assay, the Th cells that secrete IL-4 but not the Th cells that secrete IL-2 function as AC to induce T cell proliferation in the presence of various T cell mitogens (Con A, anti-CD3 mAb, anti-TCR mAb, and anti-Thy-1 mAb). The signal provided by the accessory Th2 cells occurred independently of MHC restriction, and the analysis of dose-response curves showed the involvement of a single stimulator cell. CD4, as well as CD8 expressing splenic T cells were induced to proliferate by the Th2 clones and mitogen, but mAb specific for CD4 or CD8 failed to affect the response. These findings indicate that cloned Th2 cells functioned as accessory cells and induced naive T cells to proliferate in the presence of mitogen.     

Presentation of autoantigen by human T cells.

Activated human T cells express MHC class II and have been shown to present foreign Ag to autologous T cells. We now demonstrate that MHC class II+ T cell clones can present myelin basic protein (MBP) peptide autoantigen in the absence of traditional APC to autologous MBP reactive T cell clones. MBP peptide-pulsed T cell clones specifically stimulated autologous MBP-reactive T cell clones to flux calcium and proliferate. Activation responses were peptide epitope specific and blocked by mAb to MHC class II, indicating a TCR-mediated response. In addition, mAb to the adhesion molecules LFA-3, CD2, LFA-1, CD29, and to the tyrosine phosphatase CD45 also inhibited proliferation, indicating the involvement of T to T cell interactions. In contrast to peptide Ag, T cell clones did not respond to autologous T cells pulsed with HPLC-purified MBP, suggesting that T cells are unable to process whole MBP. However, batch-purified MBP Ag preparations containing lower m.w. breakdown products were presented by T cells, indicating that naturally occurring breakdown products of autoantigens could be presented by activated T cells in vivo. These results raise the possibility that T cell presentation of autoantigen at inflammatory sites may be important in regulation of immune responses to self Ag.     

Th1 and Th2 clones differ in their response to a tolerogenic signal.

Th1 and Th2 clones specific for human gamma globulin (HGG) were compared and shown to differ in terms of the effects of tolerance induction on Ag-induced proliferation and helper activity. In developing a method to induce tolerance, splenic APC that had been pulsed with HGG and then fixed with 0.15% paraformaldehyde (HGG-FAPC) were used as a means to present Ag to the Th clones in the absence of costimulatory signals. Both Th1 and Th2 clones recognized HGG-FAPC as evidenced by their ability to proliferate to HGG-FAPC. Unlike Th2, Th1 proliferated to HGG-FAPC only in the presence of T cell-depleted allogeneic spleen cells as a source of accessory cell signals. The inability of Th1 cells to proliferate in the absence of costimulatory signals was due to Ag-specific inactivation: Th1 clones preincubated with HGG-FAPC were unable to proliferate when recultured with HGG and irradiated APC. In contrast to Th1 clones, Th2 clones showed no decrease in their Ag-induced proliferative capacity after exposure to any concentration of HGG-FAPC. However, when examined by using a second assay system, that of providing help for anti-HGG antibody production by primed B cells, Th2 preincubated with HGG-FAPC were markedly inhibited (up to 90%) in their ability to provide help. Preincubation with HGG-FAPC also inhibited the helper activity of the one Th1 clone that was found to induce a significant secondary antibody response. Taken together, the results suggest that exposure of Th1 to tolerogen in the form of HGG-pulsed fixed APC inactivates Th1 proliferative capacity, and possibly Th1 helper activity as well. Exposure of Th2 cells to a tolerogen suppresses the mechanism by which the Th2 cells provide Ag-induced B cell help, but does not inhibit the mechanism by which they proliferate to HGG. Furthermore, the results define a model that incorporates Ag processing as well as Ag presentation in the induction of tolerance in vitro.     

Human atopen-specific types 1 and 2 T helper cell clones.

Eight representative T lymphocyte clones (TLC) randomly selected from previously described panels of CD4+ housedust mite Dermatophagoides pteronyssinus (Dp)-specific TLC from atopic and nonatopic donors were studied in more detail in a comparative investigation. The TLC from the atopic donors closely resembled murine type 2 Th (Th2) cells by secreting substantial IL-4, IL-5, IL-6, TNF-alpha, and granulocyte-macrophage (GM)-CSF, minimal IFN-gamma, and relatively little IL-2. In contrast, the nonatopic's TLC resembled murine type 1 Th (TH1) cells by secreting substantial IFN-gamma, IL-2, TNF-alpha, and GM-CSF, no IL-4, and little IL-5. A difference with murine Th1 cells was their additional secretion of IL-6. These cytokine profiles were consistent upon stimulation via different activation pathways including stimulation with specific Dp Ag, mitogenic lectins, and antibodies to CD2, CD3, or CD28. The observed differences in IL-2 secretion, however, were most evident upon stimulation with anti-CD28. If TLC cells were cultured with highly purified B cells and stimulated with anti-CD3 in the absence of exogenous IL-4, IgE synthesis was induced only in cultures with the atopics' Th2 clones, which could be completely abrogated by anti-IL-4. The mere presence of exogenous rIL-4, however, did not result in IgE synthesis, nor did unstimulated TLC cells alone. But if unstimulated TLC cells (that proved not to secrete detectable amounts of cytokines) were added together with rIL-4, again IgE synthesis was induced only in cultures with the atopics' Th2 clones, suggesting the involvement of an additional, as yet unidentified accessory helper function of the atopics' Th2 clones for IgE induction. Unstimulated Th2 clones showed a significantly higher expression of CD28 than the Th1 clones, but three days after stimulation, CD28 expression was elevated to comparable levels on both subsets. When added to B cells at this time point, together with rIL-4 and anti-IFN-gamma, still only the atopics' Th2 clones supported IgE synthesis, arguing against a role for CD28 in this accessory helper function. Whereas the atopics' Th2 clones were excellent helper cells for IgE induction, a unique property of the nonatopic's Th1 clones was their cytolytic activity toward autologous APC which could be induced by specific Dp Ag and by anti-CD3. The present data provide clear evidence for the existence of Th1 and Th2 cells in man.     

Characterization of antigen processing and presentation by resting B lymphocytes

The production of antibody to a thymus-dependent Ag requires cooperation between the B cell and an Ag-specific Th cell. MHC restriction of this interaction implies that the Th cell recognizes Ag on the B cell surface in the context of MHC molecules and that the Ag-specific B cell gets help by acting as an APC for the Th cell. However, a number of studies have suggested that normal resting B cells are ineffective as APC, implying that the B cell must leave the resting state before it can interact specifically with a Th cell. Other studies, including our own with rabbit globulin-specific mouse T cell lines and hybridomas, show that certain T cell lines can be efficiently stimulated by normal resting B cells. One possible explanation for the above contradiction is that our B cells have become activated before presentation. Here we show that presentation by size-selected small B cells is not the result of nonspecific activation signals generated by the T cells or components of the medium. Also, although LPS activation does increase the efficiency of presentation by small B cells, use of large cells in place of small cells or preincubation of resting B cells with mitogenic doses of anti-Ig does not. Another possibility that we considered was that small B cells are unable to process Ag and that we had selected T cell lines that were capable of recognizing native Ag on the B cell surface. In the majority of cases, experiments with B cell lines and macrophages have shown that Ag presentation requires Ag processing, a sequence of events that includes internalization of Ag into an acid compartment, denaturation or digestion of Ag into fragments, and its return to the cell surface in the context of class II MHC molecules. The experiments reported here show that our T cell lines require an Ag processing step and that small resting B cells, like other APC, process Ag before presenting it to T cells. Specifically, we show that an incubation of 2 to 4 h is required after the Ag pulse before Ag presentation becomes resistant to irradiation. Shortly after the pulse, the Ag enters a pronase-resistant compartment. Although efficient Ag presentation requires initial binding to membrane Ig, Ag is no longer associated with membrane Ig at the time of presentation and is not presented in its intact form, because removal of membrane Ig by goat anti-Ig blocks presentation before but not after the Ag pulse.     

Rejection of mouse sarcoma cells after transfection of MHC class II genes

Th cells are stimulated by peptide Ag presented in the context of MHC class II molecules. We have reasoned that immune responses against tumors may be more efficient if tumor cells were class II Ag positive, and thereby able to directly function as APC to stimulate tumor-specific Th cell proliferation. We have tested this hypothesis by using DNA-mediated gene transfer to generate syngeneic MHC class II Ag-expressing mouse Sal sarcoma cells (Sal/Ak transfectants). Autologous A/J mice challenged i.p. or s.c. with Sal/Ak transfectants do not develop tumors, whereas A/J mice challenged with the class II negative parental Sal tumor have a high tumor incidence. Furthermore, immunization of the autologous host with Sal/Ak transfectants completely protects against subsequent challenge with wild-type Sal cells. MHC class II-expressing tumor cells, therefore, stimulate an improved tumor-specific immune response, and the immunity is cross-reactive with the class II negative tumor. Inasmuch as the transfected MHC class II gene product is not functioning as a target molecule for autologous tumor rejection, the improved immunogenicity of the Sal/Ak cells is probably due to stimulation of a tumor-specific Th cell population. The increased immunogenicity of Sal/Ak cells is, therefore, probably the result of direct presentation of Sal tumor-associated Ag in the context of tumor cell MHC class II molecules to Th lymphocytes. These studies demonstrate that induction of tumor cell MHC class II Ag expression is a potential strategy for tumor-specific immunotherapy, and suggest that tumor immunity may be enhanced by improved Th cell generation.     

Inability of human alveolar macrophages to stimulate resting T cells correlates with decreased antigen-specific T cell-macrophage binding

Alveolar macrophages (AM) from the majority of human volunteers are defective antigen presenting cells (APC) in T cell proliferation assays despite the display by the cells of HLA-D region antigens. We have confirmed that AM secrete relatively little interleukin 1 (IL 1), but addition of exogenous IL 1 did not improve the capacity of AM to initiate antigen-induced T cell proliferation. Thus, the presence of HLA-D region antigens and IL 1 is not sufficient to enable an accessory cell to act as an APC. We developed a T cell-accessory cell binding assay to investigate early events in T cell activation. AM demonstrated a diminished capacity as compared with monocytes to bind antigen-specific T cell clones. Nevertheless, AM often induced proliferation of T cell clones as effectively as monocytes, indicating that antigen display was intact. The inefficiency of AM in bind T cell clones correlated with their reduced capacity to induce resting T cells to express IL 2 receptors, secrete IL 2, and proliferate in response to antigen. Indirect immunofluorescence established that similar percentages of AM and monocytes expressed LFA molecules, but the density of the molecules was greater on monocytes than AM. A role for LFA antigens in the physical binding of T cells to monocytes was demonstrated by blocking antigen-specific binding with a monoclonal antibody to LFA-1 antigen. LFA-1 antibody also blocked the low levels of specific binding between AM and T cell clones, indicating that LFA-1-ligand interactions were operative between these two cell types. These studies indicate that there are critical cell membrane characteristics that promote binding of T cells to APC in addition to T cell receptor-antigen interactions. This combination of nonspecific and specific interactions leads to avid T cell-APC binding that may be essential for activation of resting T cells. Furthermore, we postulate that the failure to AM to act as effective APC results from an inability to bind T cells efficiently.     

The nature of the interaction between suppressor and helper T cells in the response to LDHB

Purified Lyt-1+2+ T cells were depleted of alloreactive cells by BUdR and light treatment, and then were primed in vitro against LDHB presented on allogeneic APC. Such cells could be restimulated by LDHB on the same allogeneic APC, but not by LDHB on APC syngeneic with the T cells. The restimulated T cells suppressed the proliferative response of Lyt-1+2- T cells primed and restimulated by the same antigen. The suppression, which was antigen specific, occurred after a 6-hr co-culture of the suppressor (Tse) and proliferating helper (Th) cells. The successful interaction (as measured by suppression) between allogeneic Th and Tse cells was found to be determined by the restriction specificity but not the MHC haplotype of Th cells, and the MHC haplotype but not the restriction specificity of Tse cells. Thus, suppression occurred only when the Tse cells carried genes controlling the MHC molecules that served as restriction elements for antigen recognition by the Th cells. No evidence could be obtained for the participation of APC in the Tse-Th interaction. The data suggest the interaction is based on the recognition by the Th cell of the antigen presented in the context of MHC molecules controlled by the Tse cell.