Micromethods for induction and assay of mouse mixed lymphocyte reactions and cytotoxicity

Failure to demonstrate public idiotypes on cytolytic cells with specificity for NP-coupled syngeneic cells

We have investigated whether cytolytic cells specific for hapten-coupled syngeneic cells have the same public idiotype as serum antibodies against the same hapten, NP-aminocaproyl (NP-cap). Anti-NP-cap antibodies of C57BL mice possess a public idiotype that can be detected by antisera against the whole V region of the antibody molecule or against the VH domain. Neither reagent had an effect on the cytolytic response either when they were used to sensitize the effector cells for complement killing or when used at high concentrations in the culture medium during the secondary stimulation in vitro.

Qa-1 interaction and T cell recognition of the Qa-1 determinant modifier peptide

The peptide-binding properties of the nonclassical major histocompatibility complex (MHC) class 1b molecule Qa-1 were investigated using a transfected hybrid molecule composed of the alpha 1 and alpha 2 domains of Qa-1b and the alpha 3 domain of H-2Db. This allowed the use of a monoclonal antibody directed against H-2Db whilst retaining the peptide-binding groove of Qa-1b. By comparison with classical MHC class I molecules, intracellular maturation of the chimeric molecule was inefficient with weak intracellular association with beta 2-microglobulin. However, at the cell surface the hybrid molecules were stably associated with beta 2-microglobulin and were recognized by cytotoxic T lymphocyte (CTL) clones specific for the Qa-1b-presented peptide Qdm (AMAPRTLLL). A whole-cell binding assay was used to determine which residues of Qdm were important for binding to Qa-1b and CTL clones served to identify residues important for T cell recognition. Substitutions at position 1 and 5 did not reduce the efficiency of binding and had little effect on CTL recognition. In contrast, substitutions at position 9 resulted in loss of MHC class I binding. Mass spectrometric analysis of peptides eluted from immunopurified Qa-1b/Db molecules indicated that Qdm was the dominant peptide. The closely related peptide, AMVPRTLLL, which is derived from the signal sequence of H-2Dk, was also present, although it was considerably less abundant. The mass profile suggested the presence of additional peptides the majority of which consisted of eight to ten amino acid residues. Finally, the finding that a peptide derived from Klebsiella pneumoniae can bind raises the possibility that this non-classical MHC class I molecule may play a role in the presentation of peptides of microorganisms.

Acceptance of skin grafts between mice bearing different allelic forms of beta 2-microglobulin

Single amino acid disparities in MHC class I molecules can elicit transplantation responses. Since beta 2 microglobulin (beta 2m) is noncovalently associated with class I antigens on the cell membrane we investigated whether the single amino acid polymorphism at position 85 (Asp-->Ala) in the mouse beta 2m molecule can cause skin graft rejection. A B2mb transgene was introduced into CBA(B2ma) mice which subsequently expressed both forms of beta 2m. Skin from these CBA beta 2mb transgenic mice was not rejected by the parental CBA strain. Previous studies showed that cytotoxic T lymphocyte (CTL) responses directed against beta 2mb use H2Kb as a restriction element. We therefore produced mice expressing H2Kb and H2Ab as well as beta 2mb by crossing CBA.beta 2mb mice with either CBA.Kb (CBK) transgenic mice or C3H.SW mice and used these as skin graft donors for beta 2mb negative littermates. In both cases rejection of transgenic skin only occurred when mice had received both a beta 2mb graft and an H2-disparate allograft lying adjacent in the same site. Introduction of the male specific antigen, H-Y, as a helper determinant did not result in rejection of beta 2mb skin. Neither did two CTL determinants (P91A and beta 2mb) on the same graft complement one another to elicit a transplantation response. Prior immunisation with tissues expressing the beta 2m disparity alone did not generate in vivo or in vitro beta 2mb-specific CTL responses, suggesting that this single amino acid difference is not sufficient to elicit a CTL or helper T cell response.

Presentation of endogenous acetylcholine receptor epitope by an MHC class II-transfected human muscle cell line to a specific CD4+ T cell clone from a myasthenia gravis patient

Muscle or thymic myoid cells, if induced to express MHC class II in addition to endogenous acetylcholine receptor (AChR), might present epitopes derived from the AChR to specific CD4+ T cells. These T cells could in turn initiate or maintain the anti-AChR response that is responsible for AChR loss in myasthenia gravis (MG). We transfected the AChR+ TE671 (rhabdomyosarcoma) cells with HLA-DR4 and co-cultured them with the DR4-restricted, CD4+ T cell clone (PM-A1; raised from a hyperplastic thymus of an MG patient and previously shown to recognise all forms of the AChR that contain the sequence alpha 144-156). Significant T cell activation, demonstrated both by 3H-thymidine incorporation and by lysis of the TE671 cells, was found in the presence of added alpha 144-156 and, more importantly, in the absence of exogenous antigen. These results show that MHC class II-expressing muscle or other AChR-expressing cells could present endogenous AChR to pathogenic T cells. This process may be important in the aetiology of MG.

Characteristics of a human liver allograft--derived T-cell line that exhibits suppressor activity

In an attempt to identify predominant cell populations that may mediate liver allograft dysfunction, the phenotypic and functional characteristics of lymphoid cells propagated from needle biopsy specimens of rejecting liver transplants were examined. In one case, a T-cell line of host phenotype propagated from a liver allograft biopsy demonstrated significant in vitro suppressor activity. This T-cell line (designated JB) was maintained for almost one year in culture with medium containing human recombinant interleukin 2 and with weekly stimulation by an Epstein-Barr virus-transformed B-cell line derived from the liver donor. Repeated analyses demonstrated that the JB line was phenotypically stable and predominantly CD3+ (86-93%), CD4+ (88-96%), DR+ (96%), Leu8-, CD45R-, CD16-, with a minor CD8+ cell population (less than 5%). The JB line demonstrated proliferative responsiveness upon coculture with cells expressing disparate donor HLA antigens but no in vitro cytotoxic activity. However, JB cells significantly (greater than 90%) suppressed mixed lymphocyte reaction or phytohemagglutinin stimulation of nonautologous peripheral blood lymphocytes. Supernatants of JB cells that had been cultured alone or with irradiated (6000 rads) Epstein-Barr virus-transformed donor B cells mimicked the suppressive activity of the JB cell line, either upon addition in vitro or by transient (4 hr) pretreatment of responder cells at 20 degrees C. JB cell supernatants were nontoxic and free of tumor necrosis factor activity, and their suppressive activity was dose-dependent, nondialyzable (greater than 100 kDa), not overcome by exogenous interleukin 1 or interleukin 2, and heat-resistant up to 56 degrees C. However, the suppressive activity of JB supernatants could be diminished or abrogated by treatment with high temperature (80-100 degrees C), reducing agents, trypsin, or absorption by peripheral blood lymphocytes at room temperature. The suppressive activity of JB cells and supernatants was not alloantigen-specific or major histocompatibility complex-restricted, did not shift mixed lymphocyte reaction kinetics, and was capable of inhibiting in vitro stimulation of peripheral blood lymphocytes in mixed lymphocyte reaction only when presented early in the culture. These findings provide the first evidence for a primary human allograft-derived T-cell line with suppressor-effective function.

Human suppressor T cells induced in vitro with an autologous renal allograft-derived T cell line. I. Suppressor cell induction, function, and specificity

The functional characteristics of T suppressor (Ts) cells generated from the peripheral blood lymphocytes (PBL) of a kidney transplant recipient who had excellent graft function for 1 year were examined. Ts cells were induced by co-culture of PBL with an autologous alloreactive cytotoxic T lymphocyte (CTL) line (EE-1) previously grown from a routine renal allograft biopsy of this patient performed 10 days posttransplant. The EE-1 line included CD3+ T cells of CD8+ and CD4+ phenotypes with cytotoxic specificity for disparate class 1 (HLA-B8) and class II (HLA-DR1 and 3) antigens of the kidney donor (JC). The EE-1 induced Ts cell lines (designated TsEE) were found to significantly suppress (50%-95%) autologous fresh responder EE-PBL stimulation by donor EBV-transformed cells (JC-EBV) in mixed lymphocyte reaction (MLR) assay. TsEE cells were CD3+ (98%) and predominantly CD8+ (68-80%), showed no cytotoxic activity, and were suppressive only at the early phase of MLR stimulation. In three-party cell test MLR assays, TsEE-mediated suppression appeared restricted to responder cells sharing HLA-B7 with the suppressor line, and was not abrogated by the addition of exogenous interleukin-2 (IL-2). TsEE cells also showed restricted suppression of CTL generation but not mature CTL activity. The restricted suppressor activity of TsEE lines was dependent upon their induction and restimulation with the autologous EE-1 line.

Down-regulation of cytotoxic T lymphocyte generation by two distinct suppressor-cell systems

Two distinct suppressor systems have been described that are capable of down-regulating in vivo generation of cytotoxic T cells directed toward haptenaltered self-antigens. One system, induced by hapten, involves three T cells that others have shown to function sequentially to suppress DTH. The initiator of this cascade is a T cell that is readily induced in spleens of mice injected intravenously with syngenic membrane-coupled hapten. This Ts, when triggered by the same syngeneic membrane-coupled hapten that induced it, elaborates a factor. The other two Ts arise in lymph nodes and spleens of mice painted epidermally with hapten. One of the two Ts in this set is readily armed by the factor of the first Ts. The factor confers its specificity and genetic restriction upon the accepting Ts. The latter, when properly triggered, makes a factor that is taken up by its companion Ts, which actually suppresses by way of a nonspecific factor. Whereas this Ts cascade is operative at the efferent limb of DTH, it mediates suppression only at the afferent phase of the CTL response. A distinctly different suppressor system is induced by minor locus (Mls) antigen. When Mlsd lymphoid cells are injected intravenously into Mlsc-possessing mice, an Lyt-1+ T-suppressor cell is generated that can be found in the spleen as well as among peritoneal exudate cells. This Ts interacts with macrophages to accomplish nonspecific suppression of the CTL response that is detectable both in vivo as well as in vitro. A Ts soluble product has been found to be effective to suppress CTL generation in vitro only when macrophages are present in culture. The macrophage that accomplishes suppression is I-A-. Although the afferent limb of the CTL response is down-regulated by this suppressor system, our in vitro culturing system is so structured as to make the helper T cell inactive. Thus, the mechanism of suppression must be oriented to the other early participants in the response, namely, precursor CTL, helper and differentiation factors, and/or the antigen-presenting cell.

The role of prostaglandins in the immunosuppressive effects of supernatants from adherent cells of murine decidual tissue

Supernatants from short-term cultures of murine decidual tissue (DS) were assessed for their regulatory effects on T cell lymphoproliferation and cytotoxic T lymphocyte (CTL) activity. DS non-specifically suppressed antigen- and mitogen-induced lymphoproliferation, spontaneous thymocyte proliferation, the mixed lymphocyte reaction (MLR) and CTL generation, but had no effect on CTL lytic activity. The immunosuppressive activity was lost after dialysis (14 kDa cut off). Supernatants from indomethacin-treated decidual tissue cultures (indomethacin-DS) lacked suppressive activity in the MLR, mitogen and thymocyte proliferation assays. Indomethacin-DS also showed markedly reduced or no suppressive effects on CTL generation. These findings suggest that prostaglandin production by the decidual component of the placenta could play a role in materno-fetal cellular interactions by regulating T cell lymphoproliferative responses and CTL generation.

Asialo GM1+ NK cells have opposite roles in the activation of alloreactive cytotoxic T lymphocyte (CTL) response in vitro and in vivo

The immuno-regulatory role of AsialoGM1+ murine NK cells in the induction of allogeneic cytotoxic T cell responses was studied in vivo and in vitro. Depletion of ASGM1+ cells from the (CBAxC57BL/6)F1 cells used for the foot-pad immunization of CBA mice greatly reduced the formation of allospecific CTLs. However, highly purified ASGM1+ cells were not efficient stimulators of alloCTLs in vivo by themselves. When the same genetic combination was used in alloCTL stimulation culture in vitro, ASGM1+ cells were seen to suppress the activation of the CTL response. The opposite roles of ASGM1+ cells in the alloCTL activation in vivo and in vitro were seen when both lymphoid cells (spleen cells or peripheral blood cells) and non-lymphoid cells (epidermal cells) were used as stimulators. The data presented in this paper suggest that during the alloCTL activation, ASGM1+ cells have an important enhancing role in vivo; but in vitro these cells suppress the antigen-presenting cells.

A syngeneic splenic cell antigen induces a suppressor T cell in lymph nodes that controls cytotoxic T-cell and primary antibody responses

The nonspecific suppression of immunological responses that is generated within host popliteal lymph nodes upon exposure to syngeneic normal spleen cells has been examined. The suppression, which had previously been described as being capable of preventing initiation of cytotoxic T lymphocytes (CTLs) to hapten-altered self antigens, arises within 3 to 7 days after injecting the spleen cells. Suppression was shown to be attributable to an induced T cell that was functional when transferred intravenously. Although the cell surface marker(s) on both splenic B and T cells that stimulates appearance of Ts has not yet been identified, the cells possessing the marker were not required to be viable to cause the induction. We have shown here that the Ts is fully functional when it is put in the antigenic site used for CTL immunization. The induced Ts has been identified as bearing the Lyt 2.1 cell surface marker. Furthermore, it has been shown to be insensitive to cyclophosphamide (CY), thus differentiating it from the naturally occurring Ts cell (TS0) that is known to be CY sensitive. In addition to preventing induction of CTLs toward hapten-altered self antigens, exposing popliteal lymph nodes to syngeneic spleen cells induced Ts capable of suppressing the primary IgM antibody response to sheep red blood cells. The Ts cells that suppressed the primary antibody response possessed the same Lyt cell surface markers and CY insensitivity as the Ts that mediated suppression of the CTL response. Thus, evidence that two dissimilar immunological reactions may be down-regulated by the same suppressor mechanism has been provided. Results of a kinetic study showed that the Ts prevented development of both the humoral and the cell-mediated immune responses by affecting their inductive phases. Possible targets for suppression that more than likely would have to be common to the two widely different immune responses have been indicated.

Modulation of in vitro thymidine incorporation into crypt cells from the murine small intestine

A method is described for the isolation of enriched populations of crypt cells from the murine small intestine. The method was developed to study the response of cells to various stimuli in vitro. The properties of the isolated cell preparations varied with the state of the intestinal mucosa of the mice from which they were isolated. Thus we could distinguish between cells from lactating and non-lactating mice. Polyamines, which are putative modulators of crypt cell division, failed to stimulate [3H]TdR incorporation in vitro. Lymphocyte culture supernatants suppressed [3H]TdR incorporation at dilutions of 1:4 to 1:64. Supernatants of 12-O-tetradecanoylphorbol-13-acetate-stimulated EL-4 cells and of mixed lymphocyte cultures failed to stimulate [3H]TdR incorporation of any dilution. Supernatants of concanavalin A-stimulated spleen cells gave less suppression of [3H]TdR incorporation than those of unstimulated spleen cells and stimulated incorporation at dilutions of 1:64 and 1:128. Phytohaemagglutinin stimulated [3H]TdR incorporation at high concentrations, whereas concanavalin A (con A) had no effect. This study shows that the isolated murine crypt cells may have the potential to provide a useful in vitro model for crypt cell responses to stimuli.

Assessment of immune responses to H-Y antigen in naturally inseminated and sperm-injected mice using cell-mediated cytotoxicity assays

An in vitro cell-mediated cytotoxicity assay has been used to assess immunity to the male-specific H-Y antigen in female mice after either insemination with male cells at syngeneic natural mating or after injection with syngeneic sperm cell suspensions. Lymphocytes showing specific cytotoxicity for the H-Y antigen could be recovered from both spleen and lymph nodes of female mice injected with sperm. However, insemination of male cells at natural mating did not apparently prime cytotoxic cells against the H-Y antigen in either the spleen or para-aortic lymph nodes draining the uterus of female mice mated once or repeatedly (3-10 X) in the absence of pregnancy. These results are discussed in relation to the factors regulating the immune responsiveness of the female to inseminated antigens.

Natural cytotoxic T cells (NCTC) that differ from natural killer (NK) and natural cytotoxic (NC) cells are present in Peyer's patches of mice

We have examined noninduced cytotoxicity of mouse gut associated and peripheral lymphoid tissues for a wide variety of syngeneic as well as allogeneic cell lines and lymphoblasts. Lymphoid cells from Peyer's patches were found to lyse these targets in a 3-hr chromium release assay whereas lymphoid cells from intestinal mucosa, mesenteric or peripheral lymph nodes, spleen, and thymus did not. The variety of targets toward which Peyer's patch cells were cytotoxic established the latter as nonspecific and H-2 unrestricted. The cell responsible for the lytic event was identified as possessing Thy 1.2 and Ia surface antigens. This naturally cytotoxic T cell (NCTC) was found to be adherent to nylon-wool but not to plastic plates. Although both natural killer cell (NK) and non-NK targets served as targets for the NCTC, the latter were further differentiable from NK cells by lack of asialo GM1 surface marker, which is present on NK cells. In addition, NCTC remained fully functional in mice given either of the drugs cyclophosphamide or cortisone. Each of these drugs, in the doses used, markedly reduced poly(I:C)-induced NK activity. Thus, NCTC differs from NK on the basis of the spectrum of targets against which it is functional, phenotypic surface markers, insusceptibility to stimulation with poly(I:C), and insensitivity to diminution by the immunosuppressive drugs cyclophosphamide and hydrocortisone. Since NCTC is a Thy 1.2 antigen-bearing cell and is detectable in a 3-hr cytotoxic assay, it also differs from the natural cytotoxic (NC) cell. NC lacks the Thy 1.2 marker and becomes detectable only in an 18-hr cytotoxic assay. Thus, NCTC is neither an NK nor an NC cell. We have discussed the possibility that the three naturally occurring cells may be related by being dedifferentiated descendants of an antigen-specific cytotoxic T lymphocyte (CTL). Alternatively, since NCTC is confined to an anatomical site prone to ample antigenic exposure and is still identifiable as a T cell, it may be in linear transition from the CTL to the NK or NC stages.

Inhibition of in vitro alloreactivity by cyclosporin A: evidence for an inter-individual variation in sensitivity

Cyclosporin A (CyA) is the immunosuppressive treatment of choice in preventing allograft rejection and graft-versus-host disease. However, clinical trials indicate that there may exist inter-individual variations in sensitivity to the drug. We have approached this issue by studying CyA-mediated inhibition of in vitro alloreactions, as measured by mixed lymphocyte reactions (MLR) and cell-mediated lympholysis (CML), using mouse and human normal spleen cells. The differences between individuals in the CyA concentration required for 50% inhibition of the human alloreactions were twentyfold for the MLR and fortyfold for the CML. Moreover, the CML appeared to be inhibited at lower doses of the drug. No correlation was found between inhibitory doses and variables such as the magnitude of the response, age, or human leukocyte antigen phenotype. When the same experiments were performed with mouse spleen cells, no differences were observed among eight inbred strains. The lack of demonstrable individual sensitivity of mice in relation to humans is discussed.

Genetic variation in the in vitro veto activity of bone-marrow cells

Cells exerting a veto type of suppressive activity, that is, suppressing the cytotoxic T lymphocyte formation against the class I major histocompatibility complex antigen on their surface, can be found in different lymphoid tissues, for example, in the bone marrow. In this study we show that there is variation in the vitro veto-cell activity between bone marrow cells derived from different mouse strains: bone marrow cells derived from mice carrying the non-H-2 genes of B10/B6 mice had clearly the strongest veto activity.

CPH-86, a highly purified podophyllotoxin, efficiently suppresses in vivo and in vitro immune responses

Podophyllotoxin, a component of the plant resin Podophyllin, has been used as a clinical drug for many years. Recently it has been highly purified under the denomination of CPH-86. We here demonstrate that extremely low doses of the compound efficiently inhibit antibody responses to SRBC and prolong allogeneic skin graft survival in mice. In vitro immune reactions, such as mitogen and alloantigen induced proliferation and development of cytotoxic T cells, are also suppressed in a dose dependent manner. This effect does not seem to be due to direct cellular toxicity or to a shift in the kinetic pattern of the responses.

Characterization of two suppressor cells that together prevent in vivo development of cytolytic T cells to hapten-altered self

Two suppressor cell populations that interact to down-regulate in vivo development of the cytolytic T-cell (CTL) response to trinitrophenyl-modified syngeneic spleen cells (TNP-SC) have been further characterized. Suppressor cells induced by the iv injection of trinitrophenyl-modified syngeneic spleen cells possess Thy 1.2 antigen. Their precursors are insensitive to pretreatment of host animals with cyclophosphamide (CY). Suppressor cells that arise after dermal sensitization with trinitrochlorobenzene are also Thy 1.2 antigen positive but their precursors are sensitive to pretreatment with CY. These characteristics of the two suppressor T cells (Ts) are identical to those of the two Ts that are generated by similar methodologies and that together suppress contact sensitivity (CS) to picryl chloride. Neither the CS nor CTL response was suppressed when host animals possessed only one set of Ts. In contrast to suppression of CS at the efferent phase, development of CTL was suppressed only when the two Ts were present early during sensitization (afferent phase). Since the results point to several similarities between the two sets of Ts that are active in the down-regulation of the CS and CTL responses, it is suggested that the two dissimilar immune responses directed to the same hapten, namely CS and CTL, may be controlled by the same suppressor cells. Since it appears that the two sets of Ts interact to affect different phases of the CS and CTL responses, down-regulation of each must be accomplished through different mechanisms.

Existence of suppressor cells in the spleen of allogeneic and syngeneic primiparous pregnant mice

Mixed lymphocyte reaction (MLR) and in vitro induction of cytolytic cells against alloantigens were investigated using spleen cells from primiparous mice mated allogeneically or syngeneically. One-way MLR was reduced significantly in degree not only in allogeneic but also in syngeneic pregnant mice. MLR of virgin spleen cells was suppressed when mitomycin C-treated spleen cells taken from syngeneic or allogeneic pregnant mice were added as regulator cells. These suppressive effects disappeared when regulator cells were treated with anti-Thy 1 or anti-Lyt 2 serum plus complement. Generation of cytotoxic lymphocytes from syngeneic or allogeneic pregnancy spleen cells in MLR was depressed compared with that from virgin spleen cells. The addition of pregnancy spleen cells to MLR suppressed in vitro generation of cytotoxic lymphocytes from virgin spleen cells. These results indicated that reduction of in vitro cellular responses of pregnancy spleen cells was due to suppressor cells in the spleens. These cells suppressed non-specifically the reactions to alloantigens and could be detected both in allogeneic and syngeneic primiparous pregnancies.

In vivo regulation of the cytolytic T cell response to hapten-altered self: suppressor T cells induced in the regional lymph nodes by exposure to syngeneic spleen cells

During the course of examining the in vivo development of the cytotoxic T lymphocyte (CTL) response to hapten-modified self antigens in mice, we have observed that it can be abrogated through prior exposure of the host's regional lymph nodes (LN) to normal syngeneic spleen cells (NSC). Suppression appeared to be antigen nonspecific and was best seen when animals were injected in the footpads with NSC at least 72 h before sensitization for CTL. The ability to prevent the development of the CTL response was restricted primarily to syngeneic splenic T and B cells since syngeneic thymocytes stimulated only partial suppression and syngeneic LN cells, as well as hapten-coupled syngeneic spleen cells, did not at all. Suppression appeared to be a local phenomenon in that the NSC induced transferable suppressor T cells to appear in the popliteal LN draining the footpads but not in spleens. In addition, animals splenectomized prior to injections of NSC showed abrogated CTL responses equivalent to sham-splenectomized animals indicating that the spleen does not contribute to the mechanism of suppression. Finally, when only one footpad was injected with NSC, suppression was seen in the draining popliteal node and not in the contralateral node. Taken together, the evidence suggests that the source of the suppression and the suppressor T cells may be attributed to an in vivo syngeneic mixed lymphocyte reaction occurring between responder cells of the draining LN and injected stimulator spleen cells.

Tumor immunity to murine plasma-cell tumors. VIII. Immunosuppression of the generation of cytotoxic T cells by murine plasma-cell tumor lines

Previous studies have clearly established that murine plasmacytomas suppress B-cell responses, but no effects on T-cell responses have been noted by most investigators. However, in our investigation of the tumor-associated antigens of plasmacytomas, we have found that immunosuppression plays an important role in the complex interaction between host immune T cells and tumor cells. In these investigations, varying the number of plasmacytoma cells added to in vitro induction systems separated two different effects which these cells had on the generation of cytotoxic T cells. On the one hand, when appropriate numbers were present, tumor cells acted as immunogens and stimulated the generation of specific killer cells against tumor-associated antigen or alloantigen which they expressed. In contrast, greater numbers of tumor cells exerted a profound inhibitory effect on the generation of cytotoxic activity when cells inactivated with irradiation were used. Mitomycin-C inactivation of plasmacytoma cells abrogated this inhibitory activity. In further experiments, MPC-II cells that had been inactivated with Mitomycin C were able to prime T cells in vivo, whereas priming by live tumor cells could not be detected in the same situation. It is suggested that immunosuppression by the live tumor cells may account for their inability to prime T cells in vivo. These results indicate that immunosuppression by plasmacytomas may be one of the important variables which influence the generation of cytotoxic T cells against tumor-associated antigens both in vivo and in vitro.

Enhancement of specific antitumor immunity in mice fed a diet enriched in vitamin A acetate

Age-matched male CBA mice on a conventional or a vitamin A acetate (VAOAc)-rich diet were immunized with irradiated cloned 3-methylcholanthrene- or Harvey sarcoma virus-induced (McSa-1 or HT3-2.1) sarcoma cells and then challenged with viable corresponding or unrelated (non-crossreacting) syngeneic sarcoma cells. The survival of the specifically immunized mice on the VAOAc diet was significantly prolonged in comparison with all control groups of mice as assessed by using logrank tests. Moreover, the specific immunization markedly decreased the incidence of tumors after the McSa-1 (but not HT3-2.1) challenge in a group of mice on the VAOAc diet (5% tumor incidence) compared with the equivalent group on the control diet (50% tumor incidence). Neither the VAOAc diet nor in vivo immunization alone or combined influenced natural killer cell activity. Specific T-cell-mediated cytotoxicity after in vivo priming and in vitro boosting with sarcoma cells was increased in VAOAc-fed mice. However, the marginal increase in cytotoxicity does not in itself explain the strikingly increased resistance to tumor transplants in preimmunized mice on the VAOAc diet in comparison with preimmunized mice on the control diet. The results indicate that a diet enriched in VAOAc can modify the ability of the immune system of a mouse to respond effectively to tumor antigens and can influence whether a tumor grows or regresses.

Absence of detectable cytotoxic lymphocytes in the spleens of guinea pigs immunized with allogeneic cells

Using inbred guinea pigs of strains JY 1, JY 2, 2 and 13, whose major histocompatibility gene complexes are different from each other at the B region and/or the I region, the authors aimed to detect cytotoxic thymus-derived lymphocytes (CTL) against allogeneic target cells. Various in vivo and in vitro sensitization methods that have been described for murine CTL systems were used. For detection of CTL, Con A- or PHA-induced 51Cr-labeled lymphoblasts were incubated with sensitized spleen cells or lymph node cells for 4 hr, and 51Cr released into the supernatant was assayed. Under these conditions, no significant lysis of the target cells was observed. On the other hand, significant levels of both delayed-type hypersensitivity and humoral antibodies were detected in the animals sensitized by in vivo methods.

Suppression of contact sensitivity and cell-mediated lympholysis by oral administration of hapten is caused by different mechanisms

Oral administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS), a water-soluble analog of trinitrochlorobenzene (TNCB), causes suppression of contact sensitivity (CS) to picryl chloride. We wished to determine what effect oral administration of TNBS (10mg), 10-12 days prior to sensitization, caused significant suppression of CS to picryl chloride. However, mice had to be fed at least three times at weekly intervals to cause suppression of the CTL response. CS was inhibited both at the afferent (induction) as well as at the efferent (effector) phase of the response. The unresponsiveness for CS was readily transferrable with cells from spleen, Peyer's patches, and mesenteric lymph node cells from fed mice. In contrast, although the hapten specific CTL response was significantly suppressed in mice fed three times. suppression could not be transferred with any of the aforementioned lymphoid populations. Furthermore, spleen cells from fed mice showed a significantly enhanced in vitro CTL response after stimulation with hapten-modified syngeneic stimulator cells. The results indicate that suppression of CS and of the CTL response in TNBS fed mice is probably caused by different mechanisms.

Cell surface structures required for B-cell activation with haptenated syngeneic cells

The requirement for H-2-coded antigens on the cell surface of stimulator cells used for induction of B-cell responsiveness against haptenated (fluorescein isothiocyanate (FITC)) syngeneic cells was studied using H-2-less F9 teratocarcinoma cell lines. I found that FITC-labelled F9 cells, in contrast to normal spleen cells, could not induce hapten-specific antibody synthesis. The effect of treatment of stimulator cells with glutaraldehyde or trypsin before or after hapten labelling was also analysed. It was found that regardless of the order of treatment, hapten-specific antibody synthesis could not be induced by cells treated with glutaraldehyde or trypsin. In addition, hapten-specific B-cell unresponsiveness could not be induced by FITC-labelled glutaraldehyde-treated syngeneic lymphocytes. However, cold targets treated with trypsin or glutaraldehyde efficiently blocked T-cell-mediated cytotoxicity. The requirement for H-2-coded antigens for B-cell activation against haptenated syngeneic lymphocytes is discussed.

Unresponsiveness in hapten-specific cytotoxic lymphocytes. III. Influence of H-2 and non-H-2 gene loci on the in vitro trinitrophenyl-specific CTL response following either acute or chronic in vivo treatment with trinitrobenzene sulfonic acid

The regulation of the in vitro generation of cytotoxic T lymphocytes (CTLs) directed against hapten-modified syngeneic cells has been investigated. The results indicate that acute intravenous pretreatment with water-soluble hapten, trinitrobenzene sulfonic acid (TNBS), can either positively or negatively affect the in vitro generation of trinitrophenyl (TNP)-specific CTLs. In general, mice bearing the H-2d haplotype are most likely to develop a reduced in vitro response pattern following a single acute in vivo TNBS treatment, wheras mice bearing the H-2k or H-2b haplotypes display either unchanged or augmented in vitro response patterns. We have shown that, in addition to the influences of H-2 genes, non-H-2 genes can also influence the in vitro hapten-specific CTL response following intravenous pretreatment with water-soluble hapten. Further, in two (H-2k X H-2d) F1 combinations between an H-2k strain displaying an unchanged in vitro response pattern following acute in vivo TNBS treatment and an H-2d strain displaying a reduced in vitro response pattern following similar treatment, it was observed that a single in vivo TNBS pretreatment did not induce the unresponsive state when F1-TNP stimulator cells were used. These results suggest that the mechanisms responsible for the reduced in vitro response pattern are not dominant within the F1 environment. However, when TNP-modified parental stimulators are used, a split-response pattern is observed in cells from TNBS-treated F1 mice which reflect the response patterns of the respective parents. These latter results again emphasize the influence of gene loci on the in vitro response patterns following acute TNBS treatment. In contrast to the significant influence of H-2 and non-H-2 genes on the in vitro TNP-specific response following acute in vivo TNBS treatment, these genes do not appear to significantly influence the in vitro TNP-specific response pattern following chronic TNBS treatment. Chronic TNBS treatment renders all strains tested specifically unresponsive.

Bacteria-immune system interactions. IX. Modulation of human and murine cytotoxic reactions by crude lipoteichoic acid extracted from Staphylococcus aureus

Crude lipoteichoic acid extracts of Staphylococcus aureus (SA-LTA) or Bacillus glogigii (Bg-LTA) inhibited cytotoxic reactions when added at day 0 to human or murine mixed lymphocyte reactions (MLR). The inhibition was dose dependent, and at low Sa-LTA concentrations it did not require reduction of thymidine incorporation into effector lymphocytes. In the murine system, Sa-LTA was a much more potent inhibitor than Bg-LTA. LTAs of both origin also could inhibit cytotoxic reactions when bound to stimulator cells. However, the LTA derivatized stimulator cells were much more inhibitory in the human than in the murine MLR. The inhibition of human cytotoxic reaction by Sa-LTA derivatized stimulator was not associated with a significant reduction of thymidine incorporation in effector cells.

In vivo regulation of the primary response of cytolytic T cells to hapten-altered self antigens by an inducible suppressor T cell

Tc directed toward hapten-altered self antigens have been prevented from appearing in vivo inducing tolerance with hapten-derivatized syngeneic spleen cells. When the latter cells were coinjected intravenously with hapten-tolerized spleen cells one week before attempting sensitization for Tc, the hapten-specific Tc were not generated. Tolerance induced in this manner was adoptively transferable to untreated hosts using spleen cells of tolerized animals. The cell responsible for down regulating the CML response was identified as a theta antigen-bearing cell. Three additional methods have been described in which induction of Tc could be prevented by tolerance initiated through the use of hapten-derivatized syngeneic spleen cells. Common to all four methods is a two-week interval between the initial administration of tolerogen and the start of sensitization for Tc formation.

Concanavalin A inhibits the effector phase of specific cytotoxicity

The effects of concanavalin A (Con A) on the effector phase of specific and nonspecific cytotoxicity were studied. The addition of the lectin to the cytotoxicity assay resulted in inhibition of specific cytotoxicity and induced the lysis of nonspecific targets only when the lectin was added after the target cells. Preincubation of the effector cells with the ligand strongly inhibited specific cytotoxicity and did not induce nonspecific cytotoxicity. However, preincubation of the target cells with Con A before addition to the assay had no effect on the specific lysis and strongly facilitated the lysis of nonspecific targets. The inhibitory effect was not due to the agglutinating property of the lectin, since another agglutinogenic and non-mitogenic lectin (Helix pomatia) did not inhibit cytotoxicity. Induction of effector-to-effector killing seemed unlikely, since the addition of Con A to 51Cr-labelled effector cells did not significantly enhance the release of isotope. The inhibitory effect could be reversed by a subsequent incubation of the Con A-treated effectors with alpha-methyl-d-mannoside. We suggest that Con A inhibits specific alloreactive cytotoxicity by blocking the antigen-binding receptors of T cells and induces nonspecific cytotoxicity by already activated cytotoxic T lymphocytes (CTLs) by binding to the major histocompatibility complex (MHC) antigens of the targets and creating structures mimicking allogenic MHC products that will be recognized by CTLs via the antigen-binding receptors.

Further observations on the effects of 1-thiocarbamoyl-2-imidazolidinone (TCI) on cell-mediated immunity

1-Thiocarbamoyl-2-imidazolidinone (TCI) affected several cell-mediated immune responses, including two under suppressor control. In the cutaneous delayed hypersensitivity reaction of C57BL/6J (B6) mice to 2,4-dinitro-1-fluorobenzene (DNFB). TCI produced different effects depending on when it was given relative to hapten sensitization and challenge. When given 2 days before initial sensitization, TCI (10(-9)g/kg) caused inhibition of the 24 hr ear swelling response elicited 5 days after sensitization and slight enhancement of the response elicited at 10 days. Given 2 days after sensitization, the same dose of TCI produced little effect on the day 5 elicited response but appreciable enhancement of the day 10 elicited reaction. At doses of 10(-4) to 10(-1)g/kg, TCI given to B6 mice 1 day before tolerogen decreased 2,4-dinitrobenzenesulfonic acid sodium salt (DNB SO 3NA)-induced tolerance to DNFB sensitization initiated 10 days later. In vitro, TCI at concentrations of 10(-12), 10(-12) to 10(-3), and 10(-9) to 10(-1) g/liter was demonstrated to suppress, respectively, concanavalin A (Con A)-stimulated proliferation of B6 mouse spleen cells, the one way mixed lymphocyte reaction between mitomycin-inactivated AKR mouse spleen stimulator cells and B6 mouse spleen responder cells, and the generation of cytotoxic B6 spleen cells directed against 51Cr-labeled Con A splenic lymphoblasts from AKR mice. The results indicate that TCI can affect immunological reactions under suppressor control and mimic the immunosuppressive effects of either niridazole itself in vivo or immunoactive niridazole metabolite preparations in vitro.

H-2-associated differences in replicated strains of mice divergently selected for body weight

A random-bred strain (Q) was established and divided into six replicates. Each replicate was divergently selected for 6-week weight (for over 30 generations) and each had an unselected control. We have investigated the H-2 haplotype of individual mice of the 18 selected Q strains to determine whether selection for size had also selected for H-2 or H-2-linked genes. From the results it appeared that only the H2b and H-2q haplotypes were present in the foundation stock. A large number of individuals of the six small sublines were of H-2b haplotype, while the majority of those of the six large sublines were of the H-2q haplotype. Individuals in the six control strains were H-2b, H-2q or both (i.e., H-2 heterozygotes and/or H-2 recombinants). These results suggest that control of body size is associated with H-2 or an H-2-linked gene(s).

During lymphatic regeneration, precursors for major histocompatibility complex-restricted cytotoxic T cells appear before alloreactive precursors

Mice were injected with a sublethal dose of cyclophosphamide (Cy) (300 mg/kg), and the appearance of the capacity of the regenerating spleen to form cytotoxic T lymphocytes (CTL) in response against 2,4,6 trinitrophenyl-coupled syngeneic cells or against allogeneic cells was followed. It was found that 8 da after Cy injection, the spleen contained cells that could give rise to CTL, but only 2,4,6 trinitrophenyl-specific CTL responses could be obtained at this stage. A low alloresponse was first seen 2 wk after Cy injection.

Functional and binding activity of monoclonal anti-Thy-1 antibodies: evidence for different expression of the two alleles

Monoclonal anti-Thy-1.1 and anti-Thy-1.2 antisera selected for complement-dependent cytotoxicity have high cytotoxic and binding titers on thymocytes and peripheral T cells of mouse strains bearing the appropriate Thy-1 allele. The effect of both anti-Thy=1.1 and anti-Thy-1.2 monoclonal antisera plus complement on cytoxic T cell effectors is to abrogate their activity. On the functional activity of precursor cytotoxic T cells, monoclonal antisera against the two alleles have different effects: anti-Thy1.2 plus complement removes precursor activity of Thy-1.2-bearing strains, including (Thy-1.1 X Thy-1.2) F heterozygotes, In contrast, six different anti-Thy-1.1 monoclonals, including four of the IgM class and two of the IgG class, failed to remove cytotoxic precursor activity from the splenic T cells of AKR, A. Thy-1.1 or (CBA X AKR) F1 mice. Analysis by florescence-activated cell sorting of in vitro cultured AKR spleen cells shows that Thy-1.1 antigen appears on the cel surface during the five-day culture period.

Preparative nonlytic separation of Lyt2+ and Lyt2- T lymphocytes, functional analyses of the separated cells and demonstration of synergy in graft-vs.-host reaction of Lyt2+ and Lyt2- cells

A convenient, preparative scale, nonlytic separation of mouse T lymphocytes into Lyt2.2+ and Lyt2.2- populations is reported. Immunoglobulin-negative (Ig-) spleen cells, Ig- lymph node cells, and peanut lectin-unagglutinated (PNA-) thymocytes were incubated under sterile conditions at 0 degree C with monoclonal mouse antibody to the Lyt2.2 T cell differentiation antigen. The antibody-treated cells were washed and placed in polystyrene tissue culture dishes that had been precoated with antibody to mouse Ig. Nonadherent populations were depleted to Lyt2.2+ cells and were essentially devoid of cytotoxic T lymphocyte precursors (CTLp), but contained helper activity for in vivo T-dependent IgM, IgG and IgA antibody formation. Adherent cell populations were enriched for Lyt2.2+ cells and for CTLp. The graft-vs.-host activity of the separated, adherent (Lyt2.2+) and nonadherent (Lyt2.2-) cells in the Simonsen spleen assay in neonatal (C57BL/6 x BALB/c)F1 mice was less than of unfractionated cells, but the activity of remixed Lyt2.2+ plus Lyt2.2- cells was higher than the sum of the contributions of these cells tested separately, and equal to that of the unfractionated cells. PNA- thymocytes were also separated into Ly2.2+ and Lyt2.2- populations by fluorescence-activated cell sorting. Nonlytic separation allows the recovery of the Lyt1+2+ population, which is lost in cytotoxic elimination experiments. Under the conditions described for the plate separation, the purity of the separated cells and recovery of activity approaches that of cells separated by sorting. Therefore, the plate separation offers a convenient alternative to fluorescence-activated cell sorting when large numbers (i.e. up to 5 x 10(7) positively selected cells) are needed, as in studies of in vivo cell-mediated immune reactions.

Generation of effector cells from T cell subsets. III. Synergy between Lyt-1 and Lyt-123/23 lymphocytes in the generation of H-2-restricted and alloreactive cytotoxic T cell

Lyt-123/23 and Lyt-1 T cell subsets, positively selected by separation on the fluorescence-activated cell sorter, were tested in vitro for their role in the generation of H-2-restricted and alloreactive cytotoxic T cells. It is shown that in the proliferation assay, both T cell subsets responded equally well to H-2 and non-H-2 antigens (H-Y), respectively. In contrast, none of the selected Lyt subsets, but only the mixed population containing Lyt-1 and Lyt-123/23 lymphocytes gave rise to both H-2-restricted (anti H-Y, anti-trinitrophenyl) and alloreactive (anti-H-2) cytotoxic lymphocytes. The data imply an essential role of Lyt-1 cells as inducers or helpers in the generation of all cytotoxic lymphocytes from their precursors in the Lyt-123/23 pool.

Comparison between the specificity of primary and secondary killer cells against alloantigens and hapten-modified syngeneic lymphoid cells

Cytotoxic responses of lymphoid cells from different mouse strains against syngeneic cells modified with the haptens fluorescein isothiocyanate and trinitrophenyl were investigated. Mic of the H-2k strain demonstrated strong primary in vitro hapten-specific cytotoxicity reactions, which were H-2 restricted and involved the Kk specificity. However, cells from H-2d and H-2b mice developed hapten-specific cytotoxic reactions that showed H-2 cross-reactivity. This cross-reactivity, with regard to the restriction element, was particularly evident with cells from mice that had been immunized in vivo. No cross-reaction was observed between the two haptens, and Dd target cell antigens. Similar cross-reactions were demonstrated in vitro experiments in which secondary in vitro responses were induced by stimulation with cross-reacting H-2 antigens. This finding was also investigated in allogeneic cytotoxicity. In vitro induced responses resulting in relatively weak specific cell-mediated lympholysis reactions were H-2 specific, whereas secondary in vitro responses demonstrated cross-reactivity between Dd and Db antigens. In these test systems, cross-stimulation was also demonstrated in secondary in vitro responses. These results are discussed in terms of similarities of T cell recognition of hapten-modified self antigens and of alloantigens.

Correlation between suppression of B cell anti-hapten response and generation of cytotoxic T cells induced by hapten-labelled syngeneic lymphocytes

The correlation between suppression of B cell antibody response and generation of cytotoxic T cells induced by hapten (FITC) labelled syngeneic lymphocytes was studied. Primary in vitro sensitization with lymphocytes labelled with the hapten concentrations (FITC 0.5 and FITC 0.05) previously shown to induce specific B cell unresponsiveness generated cytotoxic cells that specifically lysed haptenated syngeneic blast cells. In vivo priming with either SC-FITC 0.5 or SC-FITC 0.05 could be demonstrated after in vitro restimulation with similarly haptenated cells. Thus, cells from primed mice gave a cytotoxic response already after 3 days in culture, whereas primary responses were only observed on day 5. Furthermore, immunization was evident as an increased specific lysis at low effector/target ratios. However, no direct cytotoxicity could be detected in spleen cells from immune animals. Comparison between kinetics of in vivo development of specific antibody suppression and induction of cytotoxic cells detectable after in vitro boosting revealed no correlation between the two phenomena.

Thymus cells suppress the in vitro cytotoxic response against trinitrophenyl (TNP) modified syngeneic cells

The regulatory role of adult thymocytes in the in vitro cytotoxic cell formation against TNP-coupled syngeneic spleen cells was studied. Thymocytes are known to amplify the cytoxic response of lymph node cells against allogeneic cells. This kind of synergism was not found in the response against TNP-coupled cells; on the contrary, thymocytes had a clear suppressive effect. Thymocytes inducing this suppression must be present already at the beginning of the in vitro response. Mitotically blocked (mitomycin-C treated) thymocytes but not heat killed or lysed cells were also capable to suppress anti-TNP cytotoxicity.

Direct proof of autoreactive T-lymphocytes in experimental allergical encephalomyelitis (EAE)

A microcytotoxicity assay to prove directly against myelin basic protein directed cytotoxic T cells has been developed. Spleen and lymph node cells of myelin basic protein immunized strain 13 guinea pigs were restimulated in vitro with basic protein for 5 days and used as attacking cells. Autologous spleen cells were coated with about 10(7) molecules basic protein by hydrophobic attachment, labelled with 51Cr and used as targets. Concentration dependent lysis (74% corrected lysis) was measured with attackers gained 12 days post immunization. Controls performed using unspecific (PHA) stimulated attackers and non BE coated target showed no lysis. Lysis was shown to be MHC restricted. The test may serve as a tool for the assay of human demyelinating diseases.

On the T cell hyperreactivity of NZB mice against H-2-identical cells. Evidence for primary response characteristics and an increased helper potential

Experimental evidence presented in this paper suggests that the T cell hyperreactivity of NZB mice against H-2 identical target cells is a true primary response and not the consequence of an in vivo T cell autoimmune priming event. Based on additional data, we believe an elevated potential of T cell help to be present in NZB mice, which facilitates the observed hyperreactivity F1 hybrids of NZB and normal strains of mice inherited the capacity to hyperreact against H-2 identical cells in an H-2-unrestricted fashion. Because the hybrids tested possess both Qa-1 alleles--Qa-1b and Qa-1a--our experiments either indicate the existence of heterogeneity within the Qa-1b system or of an H-2-unrestricted response against additional target antigens. The T cell hyperreactivity might prove to be a valuable tool in further investigations of the pathomechanism of autoimmune disease.

Host age and H-2 tolerance in chimeric mice: mixed lymphocyte reactivity, cell-mediated lympholysis and responses to hapten-modified self

In order to further our understanding of the reasons for the increased susceptibility of aged animals to autoimmunity, neoplasms and infectious diseases, experiments were performed to determine the ability of an aged environment to induce and support tolerance to major histocompatibility complex (MHC) determinants as well as to support the development of a specific immune response to modified self-determinants. The degree and mechanisms of tolerance to host and donor histocompatibility antigens were studied in bone marrow chimeras of the type (C57B1/6 X CBA)F1 leads to (C57B1/6 X DBA/2)F1 (BCF1 and BDF1, respectively). BCF1 bone marrow donors were 6 weeks old and BDF1 hosts were 18 months old at the time of chimerization. Four to ten months later, chimeras were found to fully tolerant to all three parental haplotyes and competent to respond to fourth-party strains as assessed in both mixed lymphocyte reactions and cell-mediated lympholysis. Tolerance to parental haplotypes could not be attributed to active suppression of reactivity. The aged host environment proved incapable of supporting the development of anti-modified self-reactivity as attested by the fact that neither the senescent BDF1 mice nor the BCF1 leads to BDF1 chimeras established in aged hosts could respond to trinitrophenol-modified autologous parental cells. In contrast, young BDF1 mice and BCF 1 leads to BDF1 chimeras established in young adult hosts were competent to respond to trinitrophenol-modified autologous and parental cells in an MHC restricted fashion. The significance of these results to the susceptibility of aged animals to intracellular parasitic infections and neoplasia is discussed.

Quantitation of influenza virus antigens on infected target cells and their recognition by cross-reactive cytotoxic T cells

Monoclonal antibody to type-A influenza virus matrix (M)-protein was used to quantitate the appearance of M-protein on abortively infected P815 cells. After 16 h of infection with different type-A viruses, only a low amount of M-protein appears on the surface of infected cells (approximately 10(3) site/cell) in contrast to approximately 10(5) hemagglutinin molecules on each cell surface. However, virus replication is required for M-protein appearance. Analysis of solubilized membranes purified from 16-h-infected cells shows approximately 10(4) M-protein molecule/cell in the plasma membrane, a content that is consistent with the observed low surface expression, and that indicates that most of the M-protein is localized internally. We found no evidence that cross-reactive cytotoxic T cells could recognize M-protein; neither monoclonal antibody or hyperimmune anti-M-protein antiserum could inhibit T cell killing, either alone or in combination with monoclonal anti-H-2 antibody. Taken together, the low level of M-protein appearance and lack of T cell blocking by anti-M-protein antibody leaves doubt that M-protein is the antigen recognized by cross-reactive cytotoxic T cells.

Monoclonal antibodies to hemagglutinin and to H-2 inhibit the cross-reactive cytotoxic T cell populations induced by influenza

The target antigens recognized by the cross-reactive population of cytotoxic T cells on A/USSR/90/77 (H1N1) influenza virus-infected cells was studied with monoclonal antibodies to the H-2k antigen and viral hemagglutinin. The cytotoxic killing of virus-infected cells was differentially inhibited by three monoclonal antibodies to H-2k. Synergistic inhibition of cytotoxic activity was obtained with monoclonal antibodies to H-2 and to some antigenic determinants on the hemagglutinin melecule of A/USSR but not with others. Since target cells infected with other subtypes of influenza A viruses were not inhibited by any of the monoclonal antibodies to A/USSR hemagglutinin, it is suggested that the sites recognized by the cross-reactive cytotoxic T cells were sterically inhibited by the anti-A/USSR monoclonal antibodies. The results suggest that at least one of the target antigens recognized by the cross-reactive population of cytotoxic T cells is located on the hemagglutinin molecule. The present observations are in agreement with cytotoxic T cell recognition of closely situated viral and H-2 determinants.

Use and functional properties of peripheral blood lymphocytes in mice

Peripheral blood lymphocytes (PBL) were isolated and examined for their ability to respond in vitro to H-2 and H-Y antigens and also to hapten conjugated syngeneic cells. In addition, these lymphocytes were tested as antigen and target cells in in vitro mixed lymphocyte reaction and in chromium release cell mediated lympholysis respectively, as well as serving as targets for the H-2 typing of chimeric mice. Two methods were used to isolate the lymphocytes: a density gradient separation and a double water lysis technique. PBL, prepared by either method compared favourably with splenic lymphocytes in all aspects of anti-H-2 cytotoxicity but could not be used as responder for anti-H-Y cytotoxicity. In addition a method has been developed using PBL as targets for H-2 typing of both allophenic and irradiation chimeric mice. The small numbers of cells required for each of these procedures allows for the preselection of suitable mice and/or multiple experimental determinations on individual mice.

Expression of Ly-6 alloantigen during differentiation of cytotoxic T cells

We have prepared anti-Ly-6.2 by immunization of (CBA/Ca X A-Thy-1a)F1 with AKR/Crc lymphocytes and used the antiserum to study heterogencity of peripheral T lymphocytes. The Ly-6 alloantigen is found on all activated cytotoxic T cells studied, directed to a variety of different target antigens. The antiserum reveals heterogeneity among the precursors of T killer cells, i.e. allogeneic precursors are Ly-6-, whereas the generation of cytotoxic cells to hapten-modified syngeneic cells and xenogeneic cells is partially abrogated by serum pretreatment. Precursors of some in vivo primed responses are also Ly-6+. These findings indicate that the expression of Ly-6 antigen is, at least, partially related to the stage of T cell activation. The in vitro proliferative response of T cells to allogeneic Ia antigens is substantially reduced by pretreatment with anti-Ly-6.2 serum suggesting that this antiserum may be a useful tool for the study of heterogeneity in the Ly-1+ pool of T cells.