Effect of helper T cells on the primary in vitro production of delayed-type hypersensitivity to influenza virus

The history of the two-signal model of lymphocyte activation: A personal perspective

The first ideas leading to The Two-Signal Model of lymphocyte activation were published 50 years ago, but the model was not realized in one sitting. I describe the three phases that led to its contemporary formulations. A motivation underlying all these models was to generate a minimal description of what is required for antigen to inactivate and activate mature lymphocytes that, at the same time, accounts for how peripheral tolerance is achieved. I suggest the two signal model has not only provided a substantiated framework for understanding how antigen interacts differently with B cells and CD8 T cells, to result in their inactivation and activation, but its postulates are pertinent to contemporary issues concerning the inactivation and activation of CD4 T cells.

Evaluation of Cell-Mediated Immune Function Using the Cytotoxic T-Lymphocyte Assay

Evaluation of cell-mediated immunity (CMI) is a significant component in any assessment designed to predict the full range of potential immunotoxic risk underlying health risks. Among measures of CMI, the cytotoxic T-lymphocyte (CTL) response is recognized as perhaps the most relevant functional measure that reflects cell-mediated acquired immune defense against viral infections and cancer. The CTL response against T-dependent antigens requires the cooperation of at least three different major categories of immune cells. These include professional antigen-presenting cells (e.g., dendritic cells), CD4⁺ T helper lymphocytes, and CD8⁺ T effector lymphocytes. It is also among the few functional responses dependent on and, hence, capable of evaluating effective antigen presentation via both class I and class II molecules of the major histocompatibility complex (MHC). For this reason, the CTL assay is an excellent candidate for evaluation of potential immunotoxicity. This chapter provides an example of a mouse CTL assay against influenza virus that has been utilized for this purpose.

A Conversation with Cohn on the Activation of CD4 T Cells

Despite an agreement on most issues surrounding models for how lymphocytes are activated and inactivated, and arising out of the 1970 Two Signal Model of lymphocyte activation, Cohn and I have different perspectives on two critical issues concerning the activation of CD4 T cells. One issue is the origin of the first effector T helper (eTh) cells, postulated by both of us to be required to optimally activate precursor Th (pTh), that is naïve CD4 T cells, to further generate eTh cells. The second issue arises from our agreement that the antigen‐dependent CD4 T cell cooperation, that we both postulate is required to activate naïve CD4 T (pTh) cells, most likely is mediated by the operational recognition of linked epitopes. Although agreeing on the centrality of this operational mechanism, we disagree about how it might be realized at the molecular/cellular level. I respond here to issues raised by Cohn concerning these two mechanistic questions, in his response to my recent article on the activation and inactivation of mature CD4 T cells.

The cytotoxic T lymphocyte assay for evaluating cell-mediated immune function

Evaluation of cell-mediated immunity (CMI) is a significant component in any assessment designed to predict the full range of potential immunotoxic risk underlying health risks. Among measures of CMI, the cytotoxic T Lymphocyte (CTL) response is recognized as perhaps the most relevant functional measure that reflects cell-mediated acquired immune defense against viral infections and cancer. The CTL response against T-dependent antigens requires the cooperation of at least three different major categories of immune cells. These include professional antigen presenting cells (e.g., dendritic cells), CD4(+) T helper lymphocytes, and CD8(+) T effector lymphocytes. It is also among the few functional responses dependent on and, hence, capable of evaluating effective antigen presentation via both class I and class II molecules of the major histocompatibility complex (MHC). For this reason the CTL assay is an excellent candidate for evaluation of potential immunotoxicity. This chapter provides an example of a mouse CTL assay against influenza virus that has been utilized for this purpose.

Testing human biologicals in animal host resistance models

The purpose of immunotoxicity testing is to obtain data that is meaningful for safety assessment. Host resistance assays are the best measure of a toxicant's effect on the overall ability to mount an effective immune response and protect the host from infectious disease. An outline is presented for immunotoxicological evaluation using host resistance assays. The influenza virus host resistance model is useful to evaluate the overall health of the immune system and is one of the most thoroughly characterized host resistance models. Viral clearance requires all aspects of the immune system to work together and is the ultimate measure of the health of the immune system in this model. Mechanistic immune functions may be included while measuring viral clearance and include: cytokines, macrophage activity, natural killer (NK) cell activity, cytotoxic T-lymphocyte (CTL) activity, and influenza-specific IgM and IgG. Measurement of these immunological functions provides an evaluation of innate immunity (macrophage or NK activity), an evaluation of cell-mediated immunity (CMI) (CTL activity), and an evaluation of humoral-mediated immunity (HMI) (influenza-specific IgM or IgG). Measurement of influenza-specific IgM or IgG also provides a measurement of T-dependent antibody response (TDAR) since influenza is a T-dependent antigen. There are several targeted host resistance models that may be used to answer specific questions. Should a defect in neutrophil and/or macrophage function be suspected, Streptococcus pneumoniae, Pseudomonas aeruginosa, or Listeria monocytogenes host resistance models are useful. Anti-inflammatory pharmaceuticals or therapeutics for rheumatoid arthritis or Crohn's disease that target TNFalpha may also be evaluated for immunotoxicity using the S. pneumoniae intranasal host resistance assay. Marginal zone B (MZB) cells are required for production of antibody to T-independent antigens such as the polysaccharide capsule of the encapsulated bacteria that are so prominent in causing blood-borne infections and pneumonia. Intravenous infection with Streptococcus pneumoniae, an encapsulated bacterium, results in a blood-borne infection that requires MZB cells for clearance. The systemic S. pneumoniae host resistance assay evaluates whether a therapeutic test article exerts immunotoxicity on MZB cells and measures the T-independent antibody response (TIAR). Suppression of CMI or in some cases HMI may result in reactivation of latent virus that may result in a fatal disease such as progressive multifocal leukoencephalopathy (PML). The murine cytomegalovirus (MCMV) reactivation model may be used to evaluate a pharmaceutical agent to determine if suppression of CMI or HMI results in reactivation of latent virus. Candida albicans is another host resistance model to test potential immunotoxicity. Host resistance assays have been the ultimate measure of immunotoxicity testing for environmental chemicals and pharmaceutical small molecules. Human biologicals are now an important component of the drug development armamentarium for biotech and pharmaceutical companies. Many human biologicals are fusions of IgG, and/or target immune mediators, immunological receptors, adhesion molecules, and/or are indicated for diseases that have immune components. It is therefore necessary to thoroughly evaluate human biological therapeutics for immunotoxicity. Numerous biologicals that are pharmacologically active in rodents can be evaluated using well-characterized rodent host resistance assays. However, biologicals not active in rodents may use surrogate biologicals for testing in rodent host resistance assays, or may use host resistance assays in genetically engineered mice that mimic the effect of the human biological pharmacological agent.

T for two: when helpers need help

This article discusses forms of cell cooperation involving CD4 T cells and their impact on adaptive immunity. In particular, evidence will be presented in favor of cooperation among CD4 T cells of different specificity, its molecular basis and functional significance. Th-Th cooperation, or help for helpers, will be discussed in relation to the induction of anti-tumor responses and, in converse, the generation of autoimmunity. A model is proposed where Th-Th cooperation may represent the structure/function substrate for the control of self/non-self discrimination and peripheral tolerance in vivo.

A two-step, two-signal model for the primary activation of precursor helper T cells

I present here a new model for the primary activation of precursor helper T cells. Observations demonstrate that the immune system learns not to respond to extrathymic, organ-specific self-antigens because of their early appearance in development. The immune system thus discriminates between peripheral self-antigens and foreign antigens and, when mature, usually makes an immune response against only the latter. Contemporary models for the activation and inactivation of T helper (Th) function do not account for such discrimination. The model proposed here is consistent with contemporary findings and incorporates a mechanism of peripheral self-nonself discrimination.

Characterization of a cell population which amplifies the anticryptococcal delayed-type hypersensitivity response

Cell-mediated immunity to Cryptococcus neoformans can be detected by delayed-type hypersensitivity (DTH) to a culture filtrate antigen of C. neoformans. Recently, we have identified a population of cells in spleens of mice immunized with cryptococcal antigen that, when transferred to recipient mice at the time of immunization, amplifies the anticryptococcal DTH response. If the cell donor mice are treated with cyclosporin A during induction of the anticryptococcal DTH response, the amplifier cells are not induced, whereas the cells which transfer DTH (TDH cells) are induced. The purpose of this study was to characterize the amplifier cells with respect to their surface and functional properties and, in so doing, determine whether or not the amplifier cells are analogous to long-lived memory cells. We demonstrated that the amplifier cells were nylon-wool-nonadherent, antigen-specific, CD4 (L3T4+ Lyt-2-) T lymphocytes which appear in the spleens of mice 5 days postimmunization with cryptococcal culture filtrate antigen in complete Freund adjuvant. The amplifier T (Tamp) cells are not considered to be memory cells because they are relatively short-lived, being present 14 but not 18 days after the stimulating immunization. Moreover, the amplified anticryptococcal DTH response does not fulfill the criteria of the typical secondary immune (anamnestic) response in that the amplified response does not appear early relative to the appearance of the primary anticryptococcal DTH response, and it does not persist longer than the primary DTH response. We speculate that Tamp cells are not long-lived memory cells but rather act in a T-helper cell capacity to amplify the anticryptococcal DTH response.

Differences in the phenotypes of cells mediating anti-tumour immunity at various stages of tumour progression in mice

In Winn assays, T cells from donors immunized by tumour excision, or from mice with small tumours, mediate rejection of the metastasizing murine fibrosarcoma MC-2. As the mean size of primary tumours in spleen donors increases, the strength of anti-tumour activity declines, until it is frequently undetectable in spleen cells from mice with very large tumour burdens. Loss of splenic anti-tumour activity is coincident with the appearance of cells capable of suppressing an otherwise protective anti-tumour response in Winn assays. This paper defines the phenotypes of T cells mediating immunity against MC-2. Eleven or more days after tumour inoculation the proportions of tumour-bearer splenic leucocytes expressing Ly 1.2 (CD5), Ly 2.2 (CD8a) or L3T4 (CD4) surface antigens were significantly less than similar preparations from normal animals. Depletion of Ly 1.2+ or L3T4+ cells from spleen cells of donors with small tumours, or from donors immunized by tumour excision, diminished protection in the Winn assay. Depletion of Ly 2.2+ cells from these donors had no effect on immunity. In contrast, spleen cells taken from donors with large tumors lost all anti-tumour activity if pretreated with any one of anti-Ly 1.2 or anti-Ly 2.2 or anti-L3T4 antibodies in the presence of complement. These results suggest that cells bearing the Ly 2.2 marker may be important to weak immunity remaining in the spleens of mice with large tumours, but are not critical to strong immunity generated early in tumour growth, nor to that following tumour excision. That is, in addition to an Ly 1.2+, Ly 2.2-, L3T4+ spleen cell subset also seen early in the growth of the MC-2 tumour, a cell population which expresses the Ly 2.2 marker and which is important to anti-tumour immunity emerges late in tumour growth.

Helper strategy in tumor immunology: expansion of helper lymphocytes and utilization of helper lymphokines for experimental and clinical immunotherapy

Two main kinds of immune strategy are possible against neoplasia. The first potentiates a selected effector arm. In vitro culture with exogenous interleukin-2 (IL-2) increases the activity of natural killer cells and leads to the expansion of T cytotoxic lymphocytes. Systemic reinfusion of both of these cells with high doses of IL-2 mediates the regression of a variety of murine and human tumors. In an alternative strategy, a few regulatory lymphocytes turn on immune reactivity by triggering a cascade of interconnected effector functions. The efficacy of this strategy rests on the repertoire of effector mechanisms moved to action. An effective immunoregulatory maneuver is the addition of helper determinants on the surface of tumor cells. Its power can be further increased by the pre-induction of helper T lymphocytes specific to the helper determinants. This approach can be achieved in mice by coupling muramyl dipeptides to tumor cells, along with eliciting T lymphocytes specifically reactive to Bacillus Calmette-Guerin. Noncytotoxic T helper lymphocytes produce factors which recruit nonspecific (macrophages) as well as specific (cytolytic T lymphocytes) anti-tumor attacking cells. In this way protection can be afforded against primary tumors and metastases, as well as leukemia cells. As the activity of helper lymphocytes rests mostly on lymphokine release, the use of molecularly defined lymphokines mimicking T-helper functions has also been attempted. In a few experimental models, the association of low doses of IL-2 with non-reactive lymphocytes from tumor-bearing mice promotes an effective anti-tumor reaction in the host. Moreover, the combination of distinct lymphokines can also build a molecularly defined helper system able to activate in sequence non-specific and specific anti-tumor reactions in vivo. Trials intended to evaluate the clinical impact of these helper approaches in the management of human tumors are being started or are already under way.

In vitro primary induction of T cells mediating delayed footpad reaction and acquired cellular resistance to Listeria monocytogenes

We established an in vitro system generating L. monocytogenes-specific T cells primarily from unprimed spleen cells of mice. Normal spleen cells were cultured for 5 days in the presence of L. monocytogenes in vitro. Viable cells were harvested and assessed for their capacity to confer acquired cellular resistance (ACR) and delayed footpad reaction (DFR) upon local passive transfer to naive syngeneic recipient mice. When normal spleen cells were stimulated with viable L. monocytogenes, the viable cells that were recovered after 5 days of culture conferred a high level of ACR and DFR. Negative selection revealed that the effector cells obtained in primary in vitro culture were Thy 1+, L3T4+, Lyt2- cells. T cells mediating ACR could not be generated in the culture of normal spleen cells with heat-killed bacteria; however, cells mediating only DFR were generated in the presence of a large number of killed L. monocytogenes. The expression of DFR and ACR by T cells generated in this primary culture system was Listeria-specific; reactions were not observed against unrelated bacterial antigens including S. typhimurium, S. aureus, E. coli and PPD. FACS analysis of the cells in culture showed that L3T4+ and Lyt2- T cells were being enriched during culture. The primary generation of antigen-specific T cells in vitro was also possible with spleen cells from NTx mice but not with cells from nude mice, suggesting the presence of Listeria-specific precursors in NTx mice.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. III. Genetic restriction of delayed hypersensitivity augmentation factor (DAF)

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the culture supernatant of the mixture of immune T cells and specific antigen, or in the serum of mice immunized with xenogeneic erythrocytes and elicited for DTH footpad reaction. Previous experiments on the genetic restriction of this factor (DTH-augmentation factor; DAF) indicated that DAF activity was effective across the MHC-barrier in C3H/He (H-2k)--BALB/c (H-2d) system. The genetic restriction between DAF and its acceptor cells was then investigated precisely using Igh (immunoglobulin heavy chain locus)-congeneic mice: 1) Expression of DAF activity was MHC-nonrestricted, 2) but was restricted by the Igh-linked gene on the 12th chromosome, 3) such Igh-linked gene restriction was also demonstrated by an absorption test with normal spleen cells. The acceptor cells for DAF were Thy-1+,L3T4+,Lyt-2- T cells.

Studies on primed precursors of effector T cells involved in delayed-type hypersensitivity to sheep red blood cells in mice

The nature of primed precursor T cells (primed pre-TD), capable of differentiating into effector T cells (TD) that mediate delayed-type hypersensitivity (DTH), was investigated in B10 mice which were primed by intravenous (iv) injection of various doses of sheep red blood cells (SRBC). The presence of primed pre-TD was detected by the ability of T cells in the spleens from primed mice, which were treated in vitro with pertussis toxin and then transferred into naive recipient mice, to generate DTH in the recipient mice 14 days after transfer. The primed pre-TD were induced antigen specifically 1 day after mice were primed by iv injection of a suboptimal (10(3)), an optimal (10(5)), or supraoptimal (10(9)) dose of SRBC. They were replaced by TD 4 days after priming in optimally sensitized mice, while they were maintained without generating TD for at least 5 weeks after priming in mice primed with either a suboptimal or a supraoptimal dose of SRBC. They were L3T4-positive and dense cells, fractionated in the high-density layers on a discontinuous Percoll density gradient, and capable of transforming into less dense TD, fractionated in the low-density layers. These results indicate that primed pre-TD, which are induced by an antigen signal and then can be activated by a nonspecific stimulus, are present not only in responsive mice but also in unresponsive mice, suggesting that either the generation of TD from primed pre-TD or primed pre-TD alone is the decisive factor for either responsiveness or unresponsiveness.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. II. Augmentation of delayed-type footpad reaction and acquired resistance to Listeria monocytogenes by transfer of Listeria-immune serum

We previously found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the culture supernatant of the mixture of immune spleen cells and erythrocyte antigen, or in the serum of mice immunized with heterologous erythrocytes and exhibiting delayed-type footpad reaction. To elucidate whether this kind of factor (DTH-augmentation factor; DAF) participates in the establishment of DTH to various kinds of antigen besides erythrocyte antigen, we chose a bacterial antigen, Listeria monocytogenes, which is a facultative intracellular bacterium. In the present study, we demonstrated that the immune serum from mice immunized with viable Listeria augmented the delayed-type footpad reaction to Listeria. Furthermore, acquired resistance against Listeria was also augmented by the transfer of such immune serum. Such augmentation of acquired resistance was observed in sites infected locally and in the spleen of mice infected systemically. This effect was also seen in sera from mice immunized with heat-killed Listeria emulsified with complete Freund's adjuvant.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. IV. Effect of delayed-type hypersensitivity augmentation factor on in vitro induction of DTH

We found an antigen-specific factor capable of augmenting delayed-type hypersensitivity (DTH) in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR), or in the culture supernatant of the mixture of sensitized T cells and specific antigens. This factor (DTH augmentation factor; DAF) was confirmed to augment DTH in transferred recipients. In this paper, such an activity of DAF was further investigated using the system with in vitro induction and local transfer of DTH. DAF also augmented the primary in vitro induction of DTH, when spleen cells from mice transferred with the DAF-containing serum 12 hr previously or spleen cells incubated with the DAF-containing serum on ice for 2 hr were cultured with heterologous erythrocytes. DAF acted on the induction phase of DTH and augmented a typical DTH which was dependent on Thy-1-positive T cells. DAF showed antigen specificity, but was not assigned to conventional immunoglobulin. The activity of DAF was detected when nylon-wool nonadherent cells were incubated with DAF prior to the culture of those cells and antigens, but not detected when only nylon-wool adherent cells were incubated with DAF. Thus, DAF exerted its effect through binding to acceptor cells which were included in nylon-wool nonadherent spleen cells from normal mice.

Immunopharmacological actions of an extract isolated from inflamed skin of rabbits inoculated with vaccinia virus (neurotropin); enhancing effect on delayed type hypersensitivity response through the induction of Lyt-1+2- T cells

To clarify the immunopharmacological action of an extract isolated from inflamed skin of rabbits inoculated with vaccinia virus (Neurotropin), its effect on delayed type hypersensitivity (DTH) response to sheep red blood cells (SRBC) in mice was examined. Neurotropin enhanced the DTH response in C57BL/6 mice which were low responders to SRBC, but not in either BALB/c or C3H/He mice (high responders) when administered i.p. for 4 consecutive days prior to sensitization. However, Neurotropin did not affect the formation of plaque-forming cells to SRBC in C57BL/6 mice under the condition where it enhanced the DTH response. We further examined the mechanism by which Neurotropin enhanced the DTH response in C57BL/6 mice by means of cell transfer experiments. Spleen cells from mice administered Neurotropin i.p. for 4 days, but not saline, could enhance the DTH response when transferred i.v. into normal syngeneic mice just before sensitization. However, the treatment of the spleen cells with anti-Thy-1.2 + complement (C) or with anti-Lyt-1.2 + C, but not with anti-Lyt-2.2 + C, abrogated its enhancing effect. The depletion of macrophages from the cells had no effect. On the other hand, the spleen cells from mice administered Neurotropin had no enhancing effect in the effector phase of DTH response, and they showed a helper T cell activity in a DTH helper T cell assay system in which cyclophosphamide-treated mice were used as recipients. These results suggest that Neurotropin enhances the DTH response in low responder mice through the induction of Lyt-1+2- DTH helper T cells.

Antigen-specific augmentation of delayed-type hypersensitivity by immune serum factor in mice: augmentation of anti-tumor cytostatic activity

A humoral factor capable of augmenting delayed-type hypersensitivity antigen specificity (DAF) is present in the serum of mice sensitized with heterologous erythrocytes to induce a delayed footpad reaction (DFR). In the present study, a similar factor was identified when xenogeneic tumor cells were used as antigens. This factor also could augment the in vitro anti-tumor cytostatic activity against homologous tumor cells, which correlated with in vivo DFR to the same tumor cells. The cytostatic activity augmented by the transfer of this factor had the following characteristics: The activity appeared in the whole peritoneal exudate cells (PEC) from serum recipients at 4 days after the antigenic challenge. Such an activity was revealed in the collaboration of plastic dish-nonadherent and -adherent PEC as the primary and final effectors, respectively. The appearance of primary effector cells for such an activity was also accelerated in spleen and lymph node cells. However, a sufficient number of macrophages were always required as the final effectors in their functional expression. These primary effectors were sensitized T lymphocytes which produced lymphokine(s) such as macrophage-activating factor(s) and which contributed to this augmented cytostatic activity through the activation of macrophages. Thus, this immune serum factor seems to exert functional expression by accelerating the generation of lymphokine-producing delayed-type T lymphocytes, which is also responsible for cytostatic anti-tumor immunity.

Clonal analysis of T cell responses to herpes simplex virus: a HSV-specific, non cytolytic T cell clone displays specific helper activity for T cell response in vitro

A HSV-specific, Lyt 1+2- T cell clone (D7.1) was established by repetitive in vitro restimulation of in vivo HSV-1 primed draining lymph node cells with UV-inactivated homologous virus. Earlier work had shown that this clone could provide specific helper activity for HSV-1 primed B cells for antibody production in vivo. In this paper, further functional analysis has demonstrated that this clone and its subclones could also help unprimed T cells in the generation of effector DTH T cells in vitro. The helper activity was found to be antigen-specific and cell dose-dependent. In addition, this helper T cell clone showed little, if any, natural killer-like activity and was non-cytolytic towards both HSV-infected and uninfected syngeneic targets. However, they could exert potent cytotoxic activity towards P815 and EL-4 tumour targets in the presence of lectins.

Experimental systemic amyloidosis induced by immunization with syngeneic organ extracts in mice

Systemic amyloidosis was induced consistently in mice by intramuscular injection of syngeneic organ (liver and kidney) extracts mixed with CFA six times at weekly intervals. Syngeneic organ extract with CFA also induced amyloidosis of a lesser degree. All three strains of mice (C57BL/6, C3H/He, and BALB/c) injected with a syngeneic liver extract mixed with CFA developed systemic amyloidosis; the most prominent amyloid deposition occurred in C57BL/6 (B6) mice, followed by C3H/He and BALB/c. The amyloid substance deposited in these animals was identified as mouse amyloid A protein (AA). Furthermore, an organ specificity of the immunogen in inducing amyloidosis was suggested with liver and kidney extracts. Primed spleen cells of the immunized B6 mice were fractionated by a nylon-wool column and injected to normal recipient mice via the tail vein. Organs of the recipient mice developed systemic amyloidosis 8 wk after the transfer, and the most prominent histological changes occurred in the recipient mice given nylon-wool column adherent spleen cells. Using anti-Thy-1,2; Ly-1; Ly-2, antibody and complement, it was suggested that T cells, especially Ly-1,2,3+ T cell populations in the primed nylon-wool adherent cells, play an important role in the induction of systemic amyloidosis. It was shown further that the amyloidosis-inducing substance in liver extract was composed of unstable proteins or protein-bound substance.

Analysis of defective delayed-type hypersensitivity in autoimmune mice bearing lpr gene

Many functional defects of T-cells have been found in autoimmune prone, MRL/MpJ-lpr/lpr (MRL/lpr) mice. We examined the capacity of delayed-type hypersensitivity (DTH) induction and macrophage migration inhibition factor (MIF) production. MRL/lpr and C57BL/6J-lpr/lpr (B6/lpr) mice were tested for capacity of DTH by the footpad reaction to purified protein derivative of tuberculin (PPD) and lung granuloma formation after immunization with BCG-cell wall (BCGCW). In lpr mice, the ability to induce DTH against exogeneous antigenic stimulation decreased with age. The results show that the defect of DTH in lpr mice caused by deficiency of the MIF producing capacity of proliferated T-cells rather than suppressor cell activity for MIF production.

Antigen-specific augmentation of delayed-type hypersensitivity by immune serum factor in mice

The serum from C3H/He mice immunized with chicken erythrocytes (CRBC) in complete Freund's adjuvant contained a factor able to augment delayed-type hypersensitivity (DTH) antigen specifically, when transferred into naive syngeneic recipient mice before their sensitization with CRBC. This activity in immune serum appeared on Day 4 and reached a peak on Day 8 after immunization, and was enhanced when donor mice were treated with cyclophosphamide (CY) 2 days before immunization. The ability of recipient mice to respond to this factor was enhanced by CY treatment of these mice 4 days before being transferred. This factor could be discriminated from conventional antibodies. Production of this factor in the serum donor and the expression of its activity in transferred recipient was mediated by a T-cell subset which showed a low degree of thymus dependency in ontogenic development.

Two-chain disulphide-bonded structure of antigen-specific T-helper factor: both chains are necessary for activity and their interaction is I-A restricted

The molecular structure of the antigen-specific T-helper factor (ThF) which augments contact sensitivity in mice was studied. ThF was split into two types of polypeptide chain by mild reduction and alkylation; one antigen binding (which determined the specificity), the other non-antigen binding. The two chains were, by themselves, inactive but complemented each other and reconstituted biological activity. In addition, a genetic restriction was observed in the complementation of the two chains which mapped to the I-A subregion of the H-2 complex.

In vitro induction of specific T cells able to help in the generation of delayed-type hypersensitivity by thymus-dependent and type-II 'thymus-independent' antigens

An in vitro system is described which supports the primary induction of T cells able to help in the induction of delayed-type hypersensitivity. This system is used to demonstrate that hapten-Ficoll conjugates induce potent hapten-specific T cells with this function. These type-II 'thymus-independent' antigens are thus able to induce specific regulatory T cells. These helper T cells are similar to those induced by classical thymus-dependent antigens in that they are specific for antigen rather than idiotype and act by a linked mechanism.

Selective induction of delayed hypersensitivity T-effector and T-suppressor lymphocytes in vitro by haptenized bone marrow-derived macrophages

The role of various subpopulations of antigen-presenting macrophages in the induction of T-lymphocyte subpopulations has been difficult to study in the past. We have used an in vitro system of bone marrow cell culture both to induce T-effector (TDH) and T-suppressor (Ts) cells active in delayed-type hypersensitivity. Bone marrow-derived macrophages (BM-MA) grown in Teflon bag cultures were allowed to attach to culture dishes and were pulse-labeled with 2,4-dinitrobenzene sulfonate (DNBSO3). Spleen cell lymphocytes from nonsensitized BALB/c mice were cocultured with antigen-pulsed or control BM-MA for 3 days. The lymphocytes were harvested, and injected iv into BALB/c mice which were challenged within 1 hr after injection by painting the right ear with 2,4-dinitrofluorobenzene (DNFB, effector test) or sensitized with DNFB on 2 days following iv injection of the cells and challenged 5 days later (suppressor test). Ear swelling was measured 24 hr later to assess the effector or suppressor function of the in vitro educated lymphocytes. BM-MA grown for 5 days (BM-MA 5) in L-cell conditioned medium induced only TDH cells (Thy 1+, Lyt 1+2-) whereas BM-MA grown for 10 days in conditioned medium induced only Ts cells (Thy 1+, Lyt 1-2+). In both cases, induced TDH and Ts cells were antigen specific. Functionally, induced Ts cells suppressed the afferent limb of the delayed response. When DNP-BM-MA 5 and DNP-BM-MA 10 were used to induce TDH or Ts cells in vivo by subcutaneous or intravenous injection respectively, only BM-MA 5 were able to sensitize recipient mice. Both 5- and 10-day macrophage populations induced Ts cells in vivo. Functionally, these Ts cells appeared to act on the efferent limb of the delayed reaction. We conclude that different populations of antigen-presenting macrophages can preferentially induce TDH or Ts cells, perhaps depending on antigen presentation in association with class II antigens or on the functional state of the antigen-presenting cell.

Antigen-specific augmentation factor involved in murine delayed-type footpad reaction. I. Nature of augmentation factor

A humoral factor capable of augmenting antigen-specific DTH has been found in the culture supernatant of immune spleen cells and erythrocyte antigen. In this study, a similar factor was identified in the sera of mice sensitized and elicited with heterologous erythrocytes, and the nature of this factor was investigated. Elicitation with antigen was essentially required for the production of the augmentation factor in sensitized mice. The factor showed antigen specificity and antigen-binding capacity. The activity was not assigned to immunoglobulins, as demonstrated by an absorption test with rabbit anti-mouse immunoglobulin-conjugated Sepharose. The activity was stable to heating at 56 degrees C for 30 min, to changes of pH from 3 to 10, and to treatment with trypsin or neuraminidase. The molecular weight of this factor was about 200,000 to 450,000.

T helper factor in contact sensitivity: antigen-specific I-A+ helper factor is made by an Lyt-1+2-, I-A+, I-J- T cell

Antigen-specific T helper factor appears in the 24 hr supernatant of lymph node cells taken 4 days after immunization with contact sensitizer. The factor is assayed by its ability to augment the contact sensitivity response induced by haptenized spleen cells. In practice, picrylated or oxazolonated spleen cells are treated with the factor for 1 hr at 4 degrees and 4 x 10(6) cells are injected into the footpads of recipient mice. Contact sensitivity is assessed 5 days later. The factor first appears 3 days after immunization and its production depends on an Lyt-1+2-, I-A+, I-J- T cell. It is antigen-specific in its action in a criss-cross experiment, and can be absorbed with and eluted from haptenized beads. It bears I-A determinant(s) and the I-A determinant and the antigen binding site(s) occur on the same molecule. The molecular weight is around 60,000. The possible role of T helper factors in the activation of the antigen-presenting cell in the induction stage of the immune response is discussed.

Antigen-specific augmentation of delayed-type hypersensitivity by a humoral factor in the culture supernatant of immune spleen cells

Supernatants were harvested from a 24-hr culture of immune mouse spleen cells and erythrocyte antigens. Delayed footpad reactions to such heterologous erythrocytes were augmented antigen specifically when the supernatants were transferred a few hours before immunization of recipients. The augmentation factor(s) contained in the supernatants may exert its effect on the induction phase of delayed-type hypersensitivity.

Regulation of the class of immune response induced by antigen. I. Specific T cells switch the in vivo response from a cell-mediated to humoral mode

Unprimed murine spleen cells, when administered intravenously to irradiated recipients together with antigen for 7 days, are induced to display either DTH reactivity or to mount a humoral (IgM and IgG) response. The class induced depends on the number of spleen cells given to the irradiated host. A low number of cells does not support the induction of any response, a medium number only gives rise to substantial DTH reactivity, whereas a high number only mounts a humoral (IgM and IgG) response. Observations show that the higher number of T cells in a large inoculum of spleen cells, compared to the number present in a medium one, is responsible for the absence of DTH reactivity and the mounting of a humoral response. This finding suggests that the induction of DTH precursor cells may occur when fewer antigen-specific helper-T-cell-dependent signals are generated than the number of signals required to induce B-cell precursors of the IgM and IgG classes. This possibility is favored by further observations. The administration of in situ irradiated, primed helper T cells to mice reconstituted with a medium number of normal spleen cells, results both in the specific suppression of the DTH response that occurs in the absence of these primed cells and in the mounting of a humoral response.

In vivo collaboration between precursor T cells and helper T cells in the development of delayed-type hypersensitivity reaction to influenza virus in mice

Nude, athymic mice do not mount a delayed-type hypersensitivity (DTH) response to influenza A virus. A single injection of T helper cells (gamma-irradiated, 2-day immune spleen cells) or three injections over 3 days of a concanavalin-A-activated spleen cell supernatant to virus-sensitized nude mice resulted in a 'normal' DTH response when the mice were challenged with the virus. It was previously shown that the cells responsible for the reaction were T cells and required I-region compatibility. Injection of T helper cells into normal mice did not affect the level of the subsequent DTH response. However, injection of such cells into mice pretreated with anti-thymocyte serum (ATS) restored the ability of the mice to mount a DTH response. The results show that (1) nude mice contain precursor T cells for influenza virus antigen; (2) an I region-restricted response can be generated in the absence of a thymus; and (3) in vivo collaboration between DTH T-cell precursors and helper T cells can be shown to occur in congenitally nude mice and ATS-treated mice.

Regulatory mechanism of delayed-type hypersensitivity in mice. V. Augmentor cells for DTH responses

Mice primed with 1 microgram of reduced and alkylated ovalbumin (RA-OA) developed not only long-lived memory cells for delayed-type hypersensitivity (DTH), capable of differentiating into DTH-effector T cells (DTH-Te) against ovalbumin (OA) when restimulated in vitro with OA, but also spleen cells capable of augmenting recipients' DTH responses to OA when transferred into cyclophosphamide (CY)-pretreated mice. The augmenting activity in spleen cells, upon transfer, was found 7 days, but not 21 or 91 days, after priming with RA-OA, although memory DTH-Te were present throughout the period of observation. The loss of augmenting activity after day 7 of priming was not due to the presence of suppressor cells; spleen cells taken 21 days after priming failed to suppress, upon transfer, the augmenting activity in 7-day-primed spleen cells as well as induction and expression of DTH responses to OA. When 7-day-primed spleen cells were fractionated on a discontinuous bovine serum albumin density gradient, the augmenting activity was found only in the medium-density-cell layer, although memory DTH-Te were separated in the high-density layer. Augmentation of DTH-Te generation could also be demonstrated in vitro when 7-day-primed spleen cells, but not 21-day-primed spleen cells, were added to cultures of spleen cells from CY-pretreated mice. These results indicate that, in the 7-day-primed spleen, there is an augmentor cell population which is different from memory DTH-Te and interacts with CY-resistant unprimed cells to facilitate DTH-Te generation.

T cells cooperating in the induction of delayed-type hypersensitivity act via the linked recognition of antigenic determinants

Culture conditions have been established that allow the induction of delayed-type hypersensitivity (DTH) precursor cells present in a cell population derived from unsensitized spleen cells only when antigen-specific, radioresistant, Thy-1-bearing helper cells are added. This specific cellular cooperation acts via the linked recognition of two determinants on the antigen; thus, cells primed to the protein antigen fowl gamma globulin (FGG) will only allow the induction of DTH reactivity against the second antigen, burro erythrocyte (BRBC), when the conjugate FGG-BRBC is present in the cultures. The requirement for physical linkage between the two antigens has been demonstrated by the observation that DTH to BRBC is induced when the conjugate FGG-BRBC is present and not when BRBC and FGG are given an uncoupled molecules.

Regulation of delayed-type hypersensitivity to pathogens and alloantigens

Recent studies reinforce the notion that delayed-type hypersensitivity plays a key role in the host defence against microbial and intracellular parasitic infection, and in the rejection of skin allografts. F. Y. Liew reviews these studies and discusses the observation that this T-cell mediated immunity is profoundly regulated by antigen-specific suppressor T cells, some of which are restricted by products of the I-J subregion of the MHC.