Antigen recognition by H-2-restricted T cells. I. Cell-free antigen processing

The basis for the immunoregulatory role of macrophages and other accessory cells

Macrophages handle extracellular proteins and secrete diverse bioactive molecules and, therefore, influence the physiology of many tissues. They also have an important immunoregulatory role. The immune response to proteins involves the activation of the T helper subset of lymphocytes. The T helper cell is activated only when it interacts with the protein displayed on the surface of a macrophage or other accessory cell. This interaction involves restrictive proteins encoded in the major histocompatibility gene complex as well as growth-differentiating proteins.

Role of receptor-binding activity of the viral hemagglutinin molecule in the presentation of influenza virus antigens to helper T cells

The concentration of antigen required to stimulate influenza virus-specific helper T cells was observed to be dependent upon the antigenic form bearing the relevant determinant: intact, nonreplicative virus was needed only in picomolar amounts, while denatured proteins, protein fragments, or synthetic peptides were required in micromolar concentrations for a threshold level of stimulation. Antigenic efficiency of intact virus was found to result from the attachment of virus to sialic acid residues on the surface of the antigen-presenting cell since spikeless viral particles lacking the hemagglutinin molecule were much less efficient antigens for helper T cells and continuous presence of hemagglutination-inhibiting antihemagglutinin antibodies reduced efficiency of stimulation by intact virus approximately 100-fold for both hemagglutinin and internal virion proteins. Influenza virus associated rapidly with antigen-presenting cells; less than 10 min at 20 degrees C was sufficient to introduce virus for a maximal level of T-cell stimulation. This rapid attachment was blocked by antibodies to the hemagglutinin or by pretreatment of the antigen-presenting cells with neuraminidase to remove the cellular virus receptor. Following viral adsorption by antigen-presenting cells, a lag period of 30 min at 37 degrees C was required for the expression of helper T-cell determinants. One early event identified was the movement of the virus to a neuraminidase-insensitive compartment, which can occur at 10 degrees C, but which was not equivalent to expression of helper T-cell determinants. Preincubation of cells with virus at 10 degrees C for 4 h reduced the lag period of helper T-cell determinant expression to 15 min when these cells were shifted to 37 degrees C, suggesting that transition of the virus to a neuraminidase-resistant state is a required step in presentation of T-cell antigenic determinants.

Re-presentation of the hapten dinitrophenol (DNP) to a DNP-specific T-cell line

Using a DNP-specific, class II-restricted T-cell line C9, we asked whether normal spleen cells directly labeled with DNFB (DNP-SC) can stimulate DNP-specific T cells. C9 cells were established from BALB/c mice primed with syngeneic DNP-SC subcutaneously; they proliferated and produced IL-2 and MIF in a DNP-specific, I-A-restricted manner. We found that syngeneic DNP-SC alone, either unfixed or fixed with gluteraldehyde, could not stimulate C9 cells. However, when DNP-SC were added to cultures of C9 cells plus syngeneic fillers, but not allogeneic fillers, potent stimulation occurred. Allogeneic DNP-SC were also stimulatory provided the cultures contained filler cells syngeneic to the C9 responding T cells. DNP-protein conjugates, however, did not induce stimulation, indicating that the T cells are DNP specific but not hapten specific. Overnight coculture of DNP-SC and irradiated normal spleen cells also produced potent stimulator cells. However, generation of these stimulator cells was inhibited by addition of chloroquine to the culture medium. These findings indicate that syngeneic filler cells acquire DNP from the DNP-SC and re-present the hapten to the T cells in the context of IA. This process appears to require antigen processing by the filler cells. Collectively the results indicate that labeling of cell membranes with reactive haptens may not directly produce an immunogenic complex which is recognized by T cells.

The relation between major histocompatibility complex (MHC) restriction and the capacity of Ia to bind immunogenic peptides

The capacity of purified I-Ad, I-Ed, I-Ak, and I-Ek to bind to protein derived peptides that have been previously reported to be T cell immunogens has been examined. For each of the 12 peptides studied strong binding to the relevant Ia restriction element was observed. All the peptides bound more than one Ia molecule; however, for 11 of 12 peptides, the dominant binding was to the restriction element, whereas in one instance the dominant binding was to a nonrestriction element. When the peptides were used to inhibit the presentation of antigen by prefixed accessory cells to T cells, an excellent correlation was found between the capacity of a peptide to inhibit the binding of an antigen to purified Ia and the capacity of the peptide to inhibit accessory cell presentation of the antigen. Thus, the binding of peptide to purified Ia is immunologically relevant, and Ia seems to be the only saturable molecule on the surface of the accessory cell involved in antigen presentation. Inhibition analysis also indicated that all peptides restricted to a particular Ia molecule competitively inhibited one another, suggesting that each Ia restriction element has a single binding site for antigen. Cross-linking of labeled peptides to Ia followed by electrophoretic analysis and autoradiography suggested that this single binding site is made up of portions of both alpha and beta chains of Ia.

Identification of a uveitogenic cyanogen bromide peptide of bovine retinal S-antigen and preparation of a uveitogenic, peptide-specific T cell line

Peptide fragments of bovine retinal S-antigen produced by cyanogen bromide (CB) digestion have been purified and tested for their ability to induce experimental autoimmune uveoretinitis (EAU) and pinealitis (EAP) in Lewis rats. Following immunization with the various peptides in complete Freund's adjuvant, one of the peptides, CB123, was found to be potently uveitogenic. A CB123-specific, class II restricted T helper lymphocyte line (R208) prepared from one of the CB123 peptide-immunized animals by repeated in vitro selection with purified CB123 was able to transfer severe EAU and EAP to naive rats. Peptides CB36, CB46, CB51 and CB66 were immunogenic as assessed by the presence of antibodies detected in the enzyme-linked immunosorbent assay and sensitized lymphocytes found in [3H]thymidine incorporation assays using lymphocytes from the peptide-immunized rats, but they did not induce significant EAU or EAP. Antibodies induced by immunization with the peptides also bound intact S-antigen, unlike the lymphocytes which were only weakly responsive to S-antigen. Cross-reactivity of antibodies and lymphocytes from CB51 and CB66 immune animals suggested that these peptides overlap and contain a common epitope. No measurable immunity to any CB peptide or intact S-antigen was found in the animals immunized with peptide CB26. Although a T cell line (R17) raised to human S-antigen was also able to transfer EAU, it was weakly responsive to the CB123 peptide; also, the R208 line did not respond well to human S-antigen. Since both human and bovine S-antigen are uveitogenic, these results suggest that the uveitogenic epitope in CB123, which is of bovine origin, is not the same as the uveitogenic epitope of the human antigen.

Identification of a peptide binding protein that plays a role in antigen presentation

The helper T-cell response to globular proteins appears, in general, to require intracellular processing of the antigen, such that a peptide fragment containing the T-cell antigenic determinant is released and transported to and held on the surface of an Ia-expressing, antigen-presenting cell. However, the molecular details underlying these phenomena are largely unknown. The means by which antigenic peptides are anchored on the antigen-presenting cell surface was investigated. A cell surface protein is identified that was isolated by its ability to bind to a 24-amino acid peptide fragment of pigeon cytochrome c, residues 81-104, containing the major antigenic determinant for B10.A mouse T cells. This peptide binding protein, purified from [35S]methionine-labeled cells, appears as two discrete bands of approximately equal to 72 and 74 kDa after NaDodSO4/PAGE. The protein can be eluted from the peptide affinity column with equivalent concentrations of either the antigenic pigeon cytochrome c peptide or the corresponding nonantigenic peptide of mouse cytochrome c. However, it does not bind to the native cytochromes c, either of pigeon or mouse, and thus the protein appears to recognize some structure available only in the free peptides. This protein plays a role in antigen presentation as evidenced by the ability of rabbit antibodies raised against it to block the activation of an antigen-specific T-cell hybrid by antigen-presenting cells and pigeon cytochrome c. Its expression is not major histocompatibility complex-restricted in that the blocking activity of the antisera can be absorbed on spleen cells from mice of different haplotypes. This peptide binding protein can be isolated from a variety of cell types, including B cells, T cells, and fibroblasts. The anchoring of processed peptides on the cell surface by such a protein may play a role in antigen presentation--facilitating the interaction of antigenic peptides with Ia and/or the T-cell receptor.

High efficiency antigen presentation by thyroglobulin-primed murine splenic B cells

B cells primed in vivo with mouse or rat thyroglobulin present these antigens at very low concentrations to CH9, an Ly 1+2- T cell hybridoma specific for mouse and rat thyroglobulin. Presentation measured by interleukin 2 release from CH9 is sensitive to treatment with a monoclonal antibody eliminating splenic B cells but is unaffected by anti-Thy-1.2 or 33D1 (which destroy T cells and dendritic cells, respectively). Presentation is specific for the priming antigen and is blocked by preincubation of the B cells with sheep anti-mouse F(ab')2. We suggest that in this system, primed B cells present thyroglobulin and that this may represent a means by which an initial triggering event priming both B and T cells could allow maintenance of autoreactive responses in vivo in the presence of low concentrations of circulating antigen.

Antigen-specific memory and virgin B cells differ in their requirements for conjugation to T cells

The physical interaction between carrier-specific T hybridoma cells and long-term primed, TNP-specific memory B cells (TNP-MABC) exposed to TNP-OVA was compared to that of unprimed, TNP-specific virgin B cells (TNP-ABC). The direct conjugation of the T and B cells was visualized at the light microscopic level and the number of T/B conjugates was quantified directly. The results demonstrate that the TNP-MABC, as compared to TNP-ABC, formed T/B conjugates after a shorter exposure time to antigen and at a 10-fold lower concentration of antigen. Conjugate formation was inhibited almost completely by treating the TNP-MABC with concentrations of chloroquine that only partially inhibited the ability of the TNP-ABC to form conjugates. Exposure of the T hybridoma cells or the TNP-ABC to monoclonal antibodies directed against cell surface antigens prior to conjugation indicated that L3T4, Thy-1.2, and LFA-1 antigens on the T cells and LFA-1 and I-A antigens on the TNP-ABC are involved in conjugate formation. However, in contrast to the TNP-ABC where treatment of the B cells with anti-LFA-1 blocked T/B conjugate formation, pretreatment of the TNP-MABC with anti-LFA-1 had no effect.

Characterization of antigen association with accessory cells: specific removal of processed antigens from the cell surface by phospholipases

To characterize the basis for the cell surface association of processed antigen with the antigen-presenting cell (APC) we analyzed its sensitivity to enzymatic digestion. Antigen-exposed APC that are treated with phospholipase and then immediately fixed lose their ability to stimulate antigen-plus-Ia-specific T-T hybridomas. This effect is seen with highly purified phospholipase A2 and phospholipase C. In addition it is observed with three distinct antigens--ovalbumin, bovine insulin, and poly(LGlu56LLys35LPhe9) [(GluLysPhe)n]. The effect of phospholipases is highly specific. Identically treated APC are equivalent to controls in their ability to stimulate alloreactive hybridomas specific for precisely the same Ia molecule that is corecognized by antigen-plus-Ia-specific hybrids. Furthermore, the antigen-presenting function of enzyme-treated, fixed APC can be reconstituted by the addition of exogenous in vitro processed or "processing independent" antigens. In parallel studies 125I-labeled avidin was shown to specifically bind to APC that were previously exposed and allowed to process biotin-insulin. Biotin-insulin-exposed APC that are pretreated with phospholipase bind significantly less 125I-labeled avidin than do untreated, exposed APC. Identical enzyme treatment does not reduce the binding of avidin to a biotinylated antibody already bound to class II major histocompatibility complex molecules of APC. At least some of the biotin-insulin surface sites are immunologically relevant, because the presentation of processed biotin-insulin by fixed APC is blocked by avidin. This effect is specific. Avidin binding to biotin-insulin-exposed APC does not inhibit allospecific stimulation nor the presentation of unconjugated insulin. These studies demonstrate that phospholipase effectively removes processed cell surface antigen.

Induction of measles virus-specific human cytotoxic T cells by purified measles virus nucleocapsid and hemagglutinin polypeptides

The measles virus polypeptide specificity of human measles virus-specific, HLA class II restricted cytotoxic T cells have been examined. Measles virus-specific CTL have been generated using purified measles virus nucleocapsid and hemagglutinin polypeptides during a primary, in vitro stimulation of bulk cultures. Both the purified preparations of measles virus nucleocapsid and hemagglutinin polypeptides were effective in stimulating a measles virus-specific CTL response. The measles virus nucleocapsid-induced CTL response could be blocked by an anti-HLA class II monoclonal antibody but not an anti-HLA class I antiserum. Moreover, considerably less measles virus nucleocapsid was required to stimulate a comparable CTL response than the measles virus hemagglutinin which suggests that the CTL response to measles virus may be skewed towards internal viral determinants of measles virus. These studies indicate that both internal and external components of measles virus are effective in inducing measles virus-specific CTL. The recognition of internal viral components may represent an important part of the T cell mediated immune response to viruses.

The bovine autologous Theileria mixed leucocyte reaction: influence of monocytes and phenotype of the parasitized stimulator cell on proliferation and parasite specificity

In the autologous Theileria mixed leucocyte reaction (MLR), irradiated Theileria parva-infected cells induce proliferative responses in autologous peripheral blood mononuclear leucocytes (PBM), irrespective of the immune status of the donor animal. In this paper we have analysed the cellular basis of this response in naive and immune cattle to determine the Theileria specificity of the response. The magnitude of proliferation is dependent on two parameters, namely the presence or absence of monocytes in the responder population, and the phenotype of the parasitized stimulator cells, both of which appeared to be independent of the immune status of the donor animal. Monocyte-depleted responders invariably gave stronger proliferative responses but generated cytotoxicity from immune cattle that tended to be less genetically restricted. Marked differences were observed in the stimulatory capacity of cloned parasitized T-cell and non-T cell lines. At least part of this variation was associated with differences in the capacity of the parasitized cells to secrete soluble suppressive factors and possibly also stimulatory factors. Two observations indicated that, in immune cattle, part of the proliferative response in the autologous Theileria MLR is parasite-specific. First, stimulator cells fixed with glutaraldehyde stimulated proliferative responses in monocyte depleted PBM from immune animals but not naive animals. Second, in autologous Theileria MLRs with intact PBM, genetically restricted cytotoxic cells were generated from immune but not naive animals. While monocytes seem not to be required for induction of the parasite-specific component of the response, their absence from the assay when viable stimulator cells are utilized appears to enhance the non-specific component of the proliferative and cytotoxic responses.

T-cell recognition and antigen presentation of lysozyme

Several years ago, this laboratory introduced a comprehensive strategy for the systematic localization of all the continuous sites on a protein that are involved in B- and T-cell recognition. The strategy depends on the synthesis of consecutive overlapping peptides that together account for the entire protein chain. Using this approach, the full submolecular profile of continuous regions on hen egg lysozyme recognized by T cells (T sites) were localized. Four major T-cell recognition sites, three of which were subject to individual genetic control, were localized in the six mouse strains examined. In addition to these four continuous T sites, T-cell recognition of lysozyme also involved the three previously defined discontinuous antibody binding sites as demonstrated with lysozyme-specific long-term T cell cultures. Contrary to a long held impression, T-cell recognition, therefore, is not restricted only to sequence features, but can also be directed to protein discontinuous surface areas of high conformational dependency. More recently, we have examined in two mouse strains the proliferative response to peptides and to native protein of lymph node cells from mice primed with synthetic overlapping peptides either individually or as a mixture. It was found that the pattern of T-cell recognition observed after priming with peptides differs from that obtained when the native protein is used as the immunogen. If antigen processing proceeds via fragmentation, then only those regions containing T sites would be expected to be effective in priming for a T-cell response to the intact protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell growth cycle block of T cell hybridomas upon activation with antigen

Stimulation of antigen-specific T cell hybridomas with the appropriate antigen/MHC combination, at concentrations that resulted in the secretion of the lymphokine interleukin 2, resulted in a dose-dependent decrease in both [3H]thymidine incorporation and cell growth. Flow cytometric studies demonstrated that stimulation with antigen resulted in a cell cycle block that was most evident at the G1/S border, and mixing studies revealed that bystander T cells of different antigen specificities were not affected. For at least the large majority of T cells, the G1/S cell cycle block appeared to be irreversible after 24 h of exposure to antigen. This cell cycle block may be useful as a rapid and quantitative measure of T cell hybridoma activation, as a means of selecting T cell hybridomas that have functional alterations in the reception of stimulatory signals, and may serve as a model of the induction of tolerance in immature T cells.

Keratinocyte membrane-associated epidermal cell-derived thymocyte-activating factor (ETAF)

This study describes the association between secreted keratinocyte interleukin 1 (IL-1) and its presence on the keratinocyte cell surface. These properties were studied in normal and transformed human keratinocytes as well as in transformed murine keratinocytes. We will present evidence that the secretion of IL-1 by human and murine keratinocytes is associated with the presence of IL-1 on the keratinocyte membrane. In addition, although transformed murine keratinocytes secrete other cytokines, namely keratinocyte T-cell growth factor (KTGF) and IL-3, no KTGF or IL-3 activity can be demonstrated on the cell surface.

Antigen presenting cells: detection and quantification of a cytochrome c determinant important for activation of T-cells on bone marrow derived macrophages by using specific anti cytochrome c monoclonal antibody

The region of the horse cytochrome c molecule recognized by Mab SJL2-4 specific for the denatured form of the protein was located around residues 22-28. Binding studies on antigen pulsed macrophages were also performed. Surprisingly, heme peptide 1-65 was not recognised by Mab when bound on macrophages. This correlates with the incapacity of the same peptide to activate the T-cell clone 2-16. Binding sites on antigen pulsed macrophages varied between 0.5-2 x 10(6) per cell depending on the conditions used. The expression of the antigenic determinant as detected by Mab was also followed under different conditions (chloroquine, trypsin treatment) and time. Kinetics parameters of the antigen-antibody reaction in solution and on antigen bound macrophages were also determined and are dramatically different. This is correlated with a different structure of the peptide in solution and on macrophage cell surface.

T-cell recognition and antigen presentation of myoglobin

Determination of the T-cell recognition profile of Mb by the overlapping peptide strategy revealed that the protein has six T sites. Five of these coincide with the antigenic sites while one site was recognized exclusively by T cells and not by any detectable levels of antibody. Recognition of the synthetic T sites by protein-primed T cell lines or clones indicated that T cells display an unusual peptide size requirement beyond the essential contact residues of the T site. The antigen presentation of Mb has been examined with the significant advantage of knowing the full profiles of T- and B-cell recognition of this multi-determinant antigen. Significant differences in the patterns of T-cell recognition were observed following protein-priming as compared to peptide-priming. The absence of a clear relationship between these patterns of recognition presents a strong evidence against a mechanism of antigen presentation which is dependent on the generation of peptide fragments with the latter being the 'presented' species. From this new perspective, the protein molecule must be predominantly presented in its intact form.

Isolation and characterization of antigen-Ia complexes involved in T cell recognition

Using equilibrium dialysis, it has been previously demonstrated that immunogenic peptides bind specifically to the Ia molecules serving as restriction elements in the immune response to these antigens. Using gel filtration to study the formation of ovalbumin (OVA) peptide-I-Ad complexes, it is herein demonstrated that the complexes, once formed, are very stable (kd approximately equal to 3 X 10(-6) s-1), but the rate of complex formation is very slow (ka approximately 1 M-1 s-1 explaining the overall low equilibrium constant of approximately 2 X 10(-6) M. Treating the complexes with glutaraldehyde revealed that the ovalbumin peptide was cross-linked solely to the alpha chain of I-Ad. Planar membranes containing I-Ad-OVA complexes stimulated a T cell response with 2 X 10(4) less antigen than required when uncomplexed antigen was used, thus demonstrating the biologic importance of these complexes in antigen recognition.

High-affinity fluorescent peptide binding to I-Ad in lipid membranes

Membranes isolated from antigen-pulsed, antigen-presenting cells were extensively dialyzed and shown to retain the ability to present antigen to an I-Ad-restricted, antigen-specific T cell, 3DO-54.8. This ability to retain antigen on the membrane was duplicated in lysates of antigen-presenting cells as well as with pure I-A molecules in phospholipid vesicles. Measurement of the concentration of surface-associated fluorescent peptide on planar membranes prepared from antigen-pulsed phospholipid vesicles showed that about 1 peptide molecule was retained per 100 I-A molecules. We calculate that about 1000 I-A-associated peptide molecules are sufficient to stimulate the response of a single 3DO-54.8 cell. The association of fluorescent peptide with the surface depended on the presence of I-A and was blocked by unlabeled ovalbumin peptide or by a digest of hen egg lysozyme, added at the time of the pulse, but not after pulsing.

Activated human T cells can present denatured antigen

The requirements for activated, Ia-positive human T cells to present antigen were examined. Although activated T cells could present allo-Ia antigens, activated T cells could not present native, soluble protein antigens. We have now shown that activated T cells can present denatured protein antigens to stimulate proliferation of antigen-specific T-cell lines. Since denatured antigen may represent a processed form of antigen, the data suggest that activated T cells can present antigen but may not be able to process antigen as efficiently as other presenting cells. We have also shown that antigen-specific T-cell lines, which are also Ia positive, are able to present antigen to themselves, if the antigen is in a denatured form. Autopresentation requires a critical minimal cell number to stimulate proliferation, even with denatured antigen. The ability of activated T cells to present antigen may reflect an important amplification or feedback mechanism of immune regulation.

The role of LFA-1 in class II restricted, antigen-specific T-cell responses

We have studied the role of the murine lymphocyte function associated antigen-1 (LFA-1) in the major histocompatibility complex (MHC)-restricted responses of a panel of T-cell hybridomas to protein antigens. Monoclonal antibodies to LFA-1 showed a differential blocking effect in these responses that correlated with the overall "sensitivity" of a given hybrid to antigen and MHC as defined by other criteria already reported. This result differs completely from similar experiments in the CTL system where all clones regardless of their overall "avidity" for target cells are very sensitive to the blocking effects of anti-LFA-1. Further, we show that no blocking effects are observed in the response of our hybridomas when Class I or Class II transfected fibroblasts or cultured 3T3 fibroblasts are used as synthetic antigen presenting cells and the result is unaltered by preincubation of such cells with interferon-gamma (IFN-gamma).

Treponemal infection specifically enhances node T-cell regulation of macrophage activity

Hamsters experimentally inoculated in the inguinal region with Treponema pallidum subsp. endemicum develop considerable pathology at that site. We examined the cell populations from these inguinal lymph nodes to determine their intercellular responses to infection. In vitro, syphilitic-node T cells markedly suppressed C3b receptor-mediated ingestion (C3bMI) in syphilitic macrophages derived from sites both proximal and distal to the inoculation. This activity was more pronounced when node T cells rather than peritoneal T cells were used. When treponemal preparations or live treponemes were added to the coculture system, the suppression was specifically enhanced, whereas the addition of heterologous agents did not promote this effect. Syphilitic macrophages from either compartment cultured alone showed no significant inhibition of C3bMI. In parallel studies on syphilitic macrophages, we observed that the expression of Ia quickly became elevated and was sustained throughout the infection. Moreover, in vitro culturing of the syphilitic-node T cells with these macrophages did not alter this function. These observations suggest that the syphilitic node contains a subpopulation of T cells that can selectively suppress macrophage C3bMI activity and concurrently regulate their cellular response to treponemal infection.

Antigen-Ia interaction and the proteolytic processing of antigen: the structure of the antigen determines its restriction to the A or E molecule of the major histocompatibility complex

The effect of a protease inhibitor, leupeptin, on the presentation of hen egg lysozyme (HEL) to cloned T cells was investigated. We found that leupeptin-sensitive thiol proteases are apparently less involved when HEL is presented by the I-Ad molecule, than when it is presented by the I-Ed molecule. This selectivity was more of a function of the antigen than that of the Ia molecule because presentation of denatured or fragmented HEL was not sensitive to leupeptin whereas antigen presentation to a number of I-A-restricted T cell clones specific to other antigens was sensitive to leupeptin. These data demonstrate that the particular combination of major histocompatibility complex/nominal antigen recognized by a certain T cell clone may require processing of the antigen molecule through a certain group of proteases and that other combinations are independent of that particular processing pathway. Furthermore, there is a preference for a certain type of processing depending on the Ia molecule involved.

The response of T cells to soluble protein antigens and fixed antigen-presenting cells

A polyclonal population of antigen-specific T cells has been used to study the presentation of a soluble protein antigen (ovalbumin) using a B-cell line (A.20) as antigen-presenting cells. We find that glutaraldehyde-fixed antigen-presenting cells will present undegraded antigen to this polyclonal population of T cells. T-cell proliferation is observed only if an exogenous source of T-cell growth factor is added to the cultures. These findings are compared to the results obtained using antigen-specific T-cell clones or T-cell hybridomas and provide further evidence to suggest that degradation of antigen is not essential for the presentation of antigen to T cells.

Phospholipase treatment of accessory cells that have been exposed to antigen selectively inhibits antigen-specific Ia-restricted, but not allospecific, stimulation of T lymphocytes

The corecognition of antigen and class II major histocompatibility complex (MHC) molecules (Ia molecules) by the T-cell receptor is a cell surface event. Before antigen is recognized, it must be taken up, processed, and displayed on the surface of an Ia-bearing accessory cell (antigen-presenting cell, APC). The exact nature of antigen processing and the subsequent associations of antigen with the APC plasma membrane, Ia molecules, and/or the T-cell receptor are not well defined. To further analyze these events, we have characterized the processing and presentation of the soluble polypeptide antigen bovine insulin. We found that this antigen requires APC-dependent processing, as evidenced by the inability of metabolically inactivated APCs to present native antigen to antigen plus Ia-specific T-T hybridomas. The ability of the same APCs to present antigen after uptake and processing showed that this antigen subsequently becomes stably associated with the APC plasma membrane. To characterize the basis for this association, we analyzed its sensitivity to enzymatic digestion. APCs exposed to antigen, treated with phospholipase A2, and then immediately fixed lost the ability to stimulate bovine insulin plus I-Ad-specific hybridomas. In contrast, the ability of these same APCs to stimulate I-Ad allospecific hybridomas was unaffected. This effect of phospholipase is not mimicked by the broadly active protease Pronase, nor is there evidence for contaminating proteases in the phospholipase preparation. These results suggest that one consequence of antigen processing may be an antigen-lipid association that contributes to the anchoring of antigen to the APC membrane. The implications of this model are discussed.

Peptides related to the antigenic determinant block T cell recognition of the native protein as processed by antigen-presenting cells

A mouse T cell hybrid specific for pigeon cytochrome c in the context of I-Ek responds by secreting interleukin 2 when co-cultured with the native antigen and the B cell lymphoma, LK-35.2, or naive splenic B cells as antigen-presenting cells (APC). Cytochromes c and their corresponding C-terminal fragments which are not capable of stimulating the TPc9.1 cells, including the autologous mouse cytochrome c, block the T cells' response to pigeon cytochrome c. In contrast, nonstimulatory N-terminal peptides of cytochrome c, which share no homology with the antigenic peptide, do not block. Blocking is observed when the nonstimulatory cytochromes c or peptides are present in culture with the live APC and nonsaturating concentrations of pigeon cytochrome c. With tobacco hornworm moth cytochrome c as antigen, a protein for which the T cell has a higher functional affinity, the response of TPc9.1 cannot be blocked by the nonstimulatory cytochromes c or by peptides, even when limiting concentrations of the tobacco hornworm moth cytochrome c are used. When paraformaldehyde-fixed APC are employed, no native cytochrome c can stimulate the T cells, including the tobacco hornworm moth protein which with the live APC is effective at 50 to 100-fold lower concentrations than pigeon cytochrome c. However, with fixed APC the T cells are stimulated by the C-terminal fragments containing residues 81-104 of the pigeon protein or residues 81-103 of the tobacco hornworm moth protein as readily and with the same relative efficiencies as the native protein, presented by live APC. The nonstimulatory peptides, but not the native cytochromes c, block T cell activation by pigeon cytochrome c pulsed-fixed APC, indicating that the nonstimulatory peptides compete with the stimulatory pigeon cytochrome c peptides produced by the APC. This competition appears to be due to nonstimulatory peptides which associate at the APC surface and not to those acting from solution because the APC which have been incubated with pigeon cytochrome c and nonstimulatory peptides and washed free of excess antigen and peptides are not stimulatory to the T cell hybrid. It was concluded that the activation of a pigeon cytochrome c-specific T cell, which recognizes a peptide fragment of the native protein on the surface of an APC, can be blocked by an excess of nonstimulatory homologous peptides when these are also associated on the surface of the APC.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigen presentation by a B-cell line transfected with cloned immunoglobulin heavy- and light-chain genes specific for a defined hapten

The rearranged genes encoding immunoglobulin heavy (mu) and light (kappa) chains specific for the hapten 2,4,6-trinitrophenyl (Tnp) were introduced into a B-lymphoma line that bears surface IgG with an unknown specificity and expresses surface Ia molecules. A transformant expressing surface IgM specific for Tnp was obtained. The transformant was found to present Tnp-proteins to antigen (protein)-specific T cells far more efficiently than the parenteral B-lymphoma line. This artificial system, utilizing recombinant DNA technology and gene transfer, provides several approaches for the study of T-cell-B-cell interactions.

The phylogeny of macrophage function: antigen uptake and degradation by peritoneal exudate cells of two amphibian species and CAF1 mice

Equal numbers of thioglycollate mobilized peritoneal exudate cells (PEC) of the newt, Notophthalmus viridescens, the South African clawed toad, Xenopus laevis, and CAF1 mice were compared with respect to their capacity to take up and degrade soluble 14C-ovalbumin (OVA). PEC of the newt failed to take up the labeled antigen, while those of the toad incorporated only one-half as much as those of the mice. Moreover, the toad PEC degraded only 42% of the immunogen which was taken up, while PEC of the mice degraded 78% of the immunogen they had ingested during the 60-min period. Paraformaldehyde treatment of the PEC prevented antigen uptake, while chloroquine treatment prevented degradation with both species, and thus, active processes were involved. While newt PEC were unable to ingest soluble OVA, they were able to ingest and degrade OVA conjugated to sepharose during the same time period. The failure of primitive vertebrates to respond immunologically to soluble proteins appears to be due to their failure to ingest soluble immunogen.

Interaction between a "processed" ovalbumin peptide and Ia molecules

The binding of 125I-labeled immunogenic peptides to purified Ia molecules in detergent solution was examined by equilibrium dialysis. We used the chicken ovalbumin peptide ovalbumin-(323-339)-Tyr, which is immunogenic in the BALB/c mouse and restricted to I-Ad. 125I-labeled ovalbumin-(323-339)-Tyr was shown to bind to I-Ad but not to I-Ed, I-Ek, or I-Ak. This binding was inhibited by unlabeled ovalbumin-(323-339) but not by ovalbumin-(329-339), which is the longest N-terminally truncated peptide that fails to stimulate any of the I-Ad-restricted hybridomas that have been raised to ovalbumin-(323-339)-Tyr. As a further specificity control, we also used the chicken egg lysozyme peptide Tyr-(46-61), which has recently been studied by similar methods [Babbitt, B. P., Allen, P. M., Matsueda, G., Haber, E. & Unanue, E. R. (1985) Nature (London) 317, 359-361]. We have confirmed that it bound to I-Ak but not to I-Ek, I-Ad, or I-Ed. Thus, a specific interaction between Ia and antigen that correlates with the major histocompatibility complex restriction was demonstrated, strongly arguing in favor of a determinant selection hypothesis for such restriction.

The cellular pathway of antigen presentation: biochemical and functional analysis of antigen processing in dendritic cells and macrophages

The response of primed T cells to keyhole limpet haemocyanin (KLH) was used to compare the characteristics of antigen presentation by lymphoid dendritic cells, splenic and peritoneal macrophages. In a similar manner to macrophages, purified dendritic cells could be pulsed with antigen and subsequently fixed by brief glutaraldehyde fixation and still retain antigen presenting activity. Also, as previously reported for macrophages, presentation could be inhibited by chloroquine. These functional experiments suggested that the pathway of antigen presentation in dendritic cells and macrophages was similar or identical. However, biochemical studies, using radiolabelled antigen, showed that dendritic cells do not significantly degrade large proteins such as KLH to TCA-soluble form, but partially hydrolyse them to smaller peptide fragments. The significance of these results in terms of a model of the cellular pathways of antigen presentation is discussed.

Antigen presentation by epithelial cells of the rat small intestine. I. Kinetics, antigen specificity and blocking by anti-Ia antisera

Columnar epithelial cells (EC), isolated from the proximal small intestine of the rat, bind ovalbumin (OVA) by a non-specific, cold-inhibitable mechanism and continue to express Ia antigens after 24 hr culture in vitro. Lymph node T cells from rats immunized with OVA proliferate following 18 hr coculture with EC and OVA. This accessory cell function of EC is antigen-specific and is blocked by anti-Ia monoclonal antisera.

Presentation by peritoneal macrophages: modulation by antibody-antigen complexes

The effects of immune complex formation on presentation was studied. Immune complexes between an IgG2a monoclonal anti-DNP antibody and TNP-KLH were produced, and the presentation of the carrier molecule by peritoneal macrophages to KLH-primed T cells was monitored. Complex formation was found to enhance the proliferative response of the T cells. This enhancement was specific, was not mediated by lymphokine release, and required antibody with an intact Fc portion. The significance of these results in terms of immune regulation and antigen presentation is discussed.

Presentation of Candida albicans and purified protein derivative soluble antigens by Epstein-Barr virus-transformed human lymphoblastoid B-cell lines

Cells other than the macrophage can function as antigen-presenting cells (APCs). These class II-bearing accessory cells include dendritic cells, epidermal Langerhans cells, B cells, murine B-cell tumors, and human Epstein-Barr virus-transformed lymphoblastoid cell lines (EBV-LCL). We investigated the ability of EBV-LCL to present two soluble antigens, Candida albicans and purified protein derivative of tuberculin (PPD). The EBV-LCL derived from B cells of two different individuals can present both antigens to bulk cultures of autologous antigen-primed peripheral blood lymphocytes. The responses of PPD-reactive T-cell clones were weaker to PPD when presented by EBV-LCL than by PBL-APCs, with some clones responding only to PPD presented by PBL-APCs. This suggests that EBV-LCL are not equivalent to PBL monocytes in APC function, and that expression of class II major histocompatibility complex antigen is not sufficient in enabling antigen-presenting capability.

Biochemistry and biology of antigen presentation by macrophages

The presentation of antigen by macrophages has been studied. We have shown that globular proteins must be processed in endocytic vesicles of low pH prior to presentation. Some of the structural requirements of one such processed peptide have been determined, as has the affinity for Ia of that peptide. Finally, we have shown that a membrane-associated form of interleukin-1 is also required for presentation of processed antigen to T cells.

Antigen-presenting cell function of dendritic cells and macrophages in proliferative T cell responses to soluble and particulate antigens

The capacity of dendritic cells (DC) and macrophages (M phi) to present soluble and particulate antigen was tested in an ovalbumin (OVA)-specific T cell proliferation assay. In a comparative investigation we found that both DC and M phi were able to present soluble OVA, but that only M phi could present insolubilized OVA to T cells. DC were found to be able to present OVA in collaboration with M phi. The failure of DC to present insolubilized OVA is probably caused by their inability to endocytose these antigens. DC appeared not to endocytose substantial amounts of soluble OVA either. In contrast to M phi, antigen presentation by DC is not blocked by lysosomotropic drugs. Taken together, these observations suggest that DC can present soluble protein antigens without intracellular degradation.

Regulation of macrophage accessory cell activity by mycobacteria. I. Ia expression in normal and irradiated mice infected with Mycobacterium microti

CBA/Ca mice were infected by either the intravenous or intraperitoneal route with Mycobacterium microti and the subsequent changes in local macrophage populations examined. Following infection, the number of macrophages increased and they showed greater expression of both MHC Class II molecules. This response was not dependent on viability of the mycobacteria, in contrast to reports with other microorganisms such as Listeria. Studies in sublethally irradiated mice indicated that persistent antigen could give rise to a response after a period of host recovery which was radiation dose dependent. This procedure also highlighted differences in the regulation of different murine class II antigens in vivo, as seen by delayed re-expression of I-E antigens. Macrophage accessory cell function, as assessed by an in vitro T cell proliferation assay, correlated with Ia expression after fixation, but not after indomethacin treatment; this highlights the diverse nature of regulatory molecules produced by these cells.

Regulation of immune responses by I-J gene products. VI. Recognition of I-E molecules by I-J-bearing suppressor factors

Poly(Glu50Tyr50) (GT) is not immunogenic in most inbred mouse strains. GT injection produces an I-J--bearing, GT-specific T-cell--derived suppressor factor (GT-TsF1) in H-2b,d,k haplotype mice. GT-TsF1 generates second-order suppressor T cells (Ts2) in H-2a,d,k haplotype mice. Here, we show that in order for GT-TsF1 to act, the recipient strain must express I-E molecules. This suggests that T cells are not the primary target of GT-TsF1. GT-TsF1 can be presented by Ia+ A20-2J B lymphoma cells. GT-TsF1 presentation is blocked by anti-I-E, but not by anti--I-A, mAb, whereas GAT presentation is blocked by anti-I-A, but not by anti--I-E, mAbs. These data suggest that I-J recognizes (or is recognized by) I-E. The existence and role of I-J molecules in immune regulation are discussed in light of these data.