Generation of T memory cells in one-way mixed lymphocyte culture. II. Anamnestic responses of "secondary" lymphocytes

In vivo responses of alloreactive lymphocytes stimulated in vitro. Skin graft rejection mediated by MLR-Primed lymphocytes

Mouse lymphocytes that have been primed in vitro against alloantigens show a specific increase in cells reactive to the priming antigens in mixed lymphocyte response (MLR) and include cells that are specifically cytotoxic in vitro. The primed population also contains cells capable of causing rejection of skin grafts when injected into nude mice. Functional enrichment of cells capable of rejecting skin grafts bearing specific alloantigens and depletion of cells capable of rejecting a third-party graft have been shown. Priming the cells a second time in vitro may result in a moderate enrichment of cells capable of rejecting the specific graft and depletion of cells reactive to third-party skin compared with once-primed cells. These findings support the prediction that the MLR is an in vitro model of allograft responses in vivo.

Genetic specificity of primary and secondary proliferative and cytotoxic responses of human lymphocytes grown in continued culture

Human T peripheral blood lymphocytes were grown in continued culture using conditioned medium obtained from phytohaemagglutinin-stimulated, pooled human leucocytes. These cultured T cells (CTC) were tested in mixed lymphocyte culture (MLC) and cell-mediated lympholysis (CML) assays to determine the genetic specificity of their proliferative and cytotoxic responses. Primary responses were measured after initial in vitro stimulation by allogeneic cells, and secondary responses were measured after a second in vitro stimulation by allogeneic cells. Both primary and secondary proliferative responses were found to be stimulated by alloantigens controlled by the HLA region and, more specifically, by antigens of the HLA-D region, in accordance with the responses of normal peripheral blood T lymphocytes. When CTC were established from unsensitized PBL and then stimulated with allogeneic cells, they could respond by proliferation in MLC, but, in contrast to PBL, they did not show subsequent cytotoxic responses. On the other hand, CTC established from PBL that had been stimulated first with allogeneic cells in either primary or secondary MLC displayed high levels of cytotoxic reactivity in CML. The strongest cytotoxicity was directed against allospecificities controlled by the HLA region and specific for the MLC-stimulating cells, but lower levels of cross-reactive cytotoxicity were also observed.

Alloantigen-induced suppressor- and memory cells in chronic lymphocytic leukemia

T cell function was evaluated in patients with B cell type of chronic lymphocytic leukemia (CLL). Unseparated peripheral blood lymphocytes (PBL) and T cells from CLL patients stimulated in a primary allogeneic MLR were able to inhibit significantly a second MLR between the original responder (CLL) and stimulator (normal PBL) cell donors. Furthermore, it is shown the T lymphocytes from patients with CLL develop immunologic memory during the course of a primary MLR as evidenced by an enhanced response in secondary MLR. These results are discussed with respect to recently described imbalances of T cell subpopulations in CLL.

Cell-growth kinetics and karyotype analysis of human memory lymphocytes responding to alloantigen and mitogen

Peripheral-blood lymphocytes were primed in vitro with the mitogen phytohemagglutinin (PHA) or with allogeneic cells and their memory responses studied following sequential restimulation with either mitogen or alloantigen. Chromosome preparations were made every 24 hours following exposure to the stimulating agents. Cultures were labeled with BUdR for sister-chromatid staining of the chromosomes which provided information about the kinetics of cell growth and rates of sister chromatid exchange. Cultures containing n BUdR were used for the investigation of cell karyotypes after chromosome-banding. Following PHA as well as alloantigen restimulation, an earlier reaction of the responding cells was observed. The peak response after the first stimulation was found at 120 h with allogeneic stimulation and at 60 h with mitogen stimulation. In the second round of stimulation, the peak occurred after 48 h (allogeneic) and 36 h (PHA) and following the third stimulation after 36 h (allogeneic) and 24 h (PHA). The speed of cell growth was decreased following restimulation with either alloantigen and mitogen. In contrast to the allogeneic restimulation, the number of cells responding after PHA restimulation was decreased. No systematic numerical or structural aberration of the karyotype was detected following repeated stimulation with either alloantigen or mitogen. In this sense, the lymphocyte subpopulations selected by repeated stimulation did not differ from the starting material. On the other hand, the sister-chromatid exchange (SCE) frequency was increased following allogeneic restimulation, whereas it remained constant with PHA restimulation.

Enrichment of MLR-activated human suppressor cells by discontinuous density-gradient centrifugation

6-day allogeneic mixed lymphocyte cultures (MLR) were fractionated on a four-step discontinuous Percoll gradient. The various fractions were added as regulatory cells to freshly established micro-MLRs between the original or third-party cell donors. Unspecific suppressor activity was highly enriched in gradient fraction III (density 1.069--1.062 g/ml), consisting mainly of blast-like cells. Suppressor cells were non-adherent T cells as determined by their spontaneous rosette formation with sheep erythrocytes and their susceptibility to lysis by anti-T-cell globulin plus complement. Mitomycin C treatment diminished their inhibitory capacity. In addition, gradient fraction III was also enriched with alloantigen-activated memory cells. By contrast, unprimed alloreactive cells were recovered from gradient fraction IV (density greater than or equal to 1.070 g/ml), consisting mainly of small, resting lymphocytes.

Tuberculous meningitis: immune reactions within the central nervous system

Cerebrospinal fluid (CSF) lymphocytes from two patients with tuberculous meningitis proliferated stronger than the corresponding peripheral blood lymphocytes (PBL) when stimulated with tuberculin purified protein derivative (PPD) in the lymphocyte transformation test after 3 days of culture. This might indicate an accumulation of specifically primed lymphocytes within the central nervous system. CSF lymphocytes and PBL from nine of ten patients with acute aseptic meningitis investigated as controls showed no or low responses when stimulated with PPD, whereas the remaining patient displayed a significant proliferation of CSF lymphocytes, which was more pronounced than that of PBL. Stimulation with the mitogens phytohaemagglutinin, concanavalin A, and pokeweek mitogen gave lower proliferation of CSF lymphocytes compared with PBL in tuberculous and aseptic meningitis. Evaluation of the proliferative response of CSF lymphocytes compared with PBL on stimulation with PPD might be a useful complement in the diagnosis of tuberculous meningitis.

Quantitative studies of alloantigen-reactive human lymphocytes in primary and secondary MLC

The number of alloantigen-reactive cells in human peripheral blood was estimated by a limiting dilution analysis. In MLC combinations between allogeneic unrelated donors, the frequency of alloantigen-reactive cells ranged between 1:241 to 1:486. The frequency of alloantigen-reactive cells to the specific donor was increased six- to eight-fold after priming in MLC. The results demonstrate that specific "memory" cells are enriched in long-term MLC. In limiting dilution experiments between HLA-identical siblings, the frequency of alloantigen-reactive cells ranged from 1:1160 to 1:1740. The data point to the existence of a lymphocyte-defined antigen system controlled by a genetic region that is not linked to HLA. The results suggest that the lymphocyte clones that are able to react to non-HLA antigens probably consist of a small number of lymphocytes. Finally, the response of these clones of cells to non-HLA antigens was observed only under conditions where responder cells were limiting.

Clones of alloreactive T cells. I. A. unique homozygous MLR-stimulating determinant present on B6 stimulators

We have developed a method which allows us to clone and reclone primed responder T cells derived from serially restimulated murine mixed lymphocyte cultures. We have derived clones from two such mixed lymphocyte cultures, A anti-B6 [A(B6)] and A anti-(B6XA)F1 [A(B6A)]. In the A (B6) system, we have isolated clones which can ve stimulated by B6 but not by (B6XA)F1 cells. This implies the presence of a unique parental H-2b MLR determinant which is absent on semi-allogeneic (B6XA)F1 cells. In the A(B6A) system, we have isolated clones which can be stimulated by (B6XA)F1 cells but not by B6 cells. This confirms our previous observation on the presence of unique hybrid MLR stimulating determinants on (B6XA)F1 cells. Many of the "clones" derived primarily from soft agar seem to be contaminated and contain several different sets of primed responder cells with different reactivity patterns . Experiments in which we subclone cells exhibiting selected reactivity patterns from such contaminated primary clones suggested that a T-cell growth factor or accessory cell is required for proliferation in soft agar following all antigen recognition by primed responder cells.

HLA-D region products are expressed in endothelial cells

The mixed lymphocyte endothelial cell culture was studied by the primed lymphocyte typing (PLT) technique. By comparing the HLA-D/DR specificity of the secondary response when using either peripheral blood mononuclear cells (PBM) or endothelial cells from umbilical cords for priming or restimulation of lymphocytes, it was found that PBM from newborn would induce a clear-cut specificity for HLA-D/DR when used for priming a well a for restimulation. No HLA-D/DR specificity was seen, however, when endothelial cells were used for restimulation of lymphocytes primed to HLA-D/DR on PBM. On the other hand, lymphocytes primed to endothelial cells showed significant, albeit not very strong specificity for HLA-D/DR when restimulated with PBM. Our experiments suggest that HLA-D region products are present on endotheial cells, and thus confirm and extend serological studies using anti DR antisera.

The specificity of secondary MLC assayed by titration of primed lymphocyte populations

The specificity of responses in secondary MLC was studied by titration (100 x 10(3) to 5 x 10(3)) of responder primed lymphocytes. In all instances, significant proliferative responses of responder primed lymphocytes to the specific stimulator occurred using lower responding cell numbers. When tested against allogeneic stimulating donors, three patterns of responses were observed: no significant responses, responses only at higher (100 x 10(3)) responding cell densities, and responses at lower responding cell densities, similar to those with the priming donor. In instances where primed lymphocytes responded significantly to allogeneic stimulating cells at lower cell densities, the responses were considered positive and the stimulating cells positive for the PL determinant. In several instances, primed lymphocytes responded significantly to allogeneic stimulators negative for the specific HLA-D and/or HLA-DR specificities. On the other hand, in experiments where allogeneic stimulating donors shared either HLA-D or DR specificity with the priming donor, a significant response was always observed. Thus, the PL determinant was present on stimulating allogeneic cells negative for specific HLA-D and DR specificities. The present data suggest that an analysis of the specificity of primed populations could be profoundly affected by the responder cell density at which the assay is performed. Also, the data suggest that other MHC determinants, including non-HLA loci may be important in secondary MLC.

Clonal priming of human lymphocytes with soluble microbial antigens: high-dose paralysis, restoration, and autologous leukocyte preference

Lymphocytes stimulated in appropriate leukocyte cultures undergo blastogenesis and proliferation for a finite period of time. With specific antigens the proliferative response peaks usually between 4 and 8 days, after which the blastoid cells revert to small lymphocytes. Lymphocytes "primed" in this manner can be restimulated to proliferate only by the same antigen with which they were incubated and only with an adequate amount of a self-specific, autologous, somatic product(s). First or "primary" leukocyte cultures stimulated by optimal or supraoptimal concentrations of soluble protein antigens (purified protein derivative (PPD), tetanus toxoid, Candida albicans) will undergo proliferation in the first culture, but the increased number of small lymphocytes that can be visualized after 10--14 days often fail to respond to any stimulus in second (secondary) or "primed" cultures. However, when fresh X-irradiated autologous cells are re-added in appropriate amounts, vigorous accelerated proliferation takes place. Addition of allogeneic cells to antigen-primed populations has one of three effects: (1) no effect (complete restriction); (2) in some instances allogeneic cells restore a significant response to the specific antigen but almost never to the same degree as autologous cells; and (3) allogeneic cells can also induce high levels of accelerated responsiveness without added antigen. These findings are discussed in the context of a working hypothesis that self-specific factors are involved in all specific immune responses. The combination of antigen and self-specific factors may lead to a quantitatively unique immune response to all antigens in each individual. The preferential response to antigen in conjunction with autologous rather than allogeneic leukocytes suggests that self-specific products are required for recognition of soluble microbial antigens.

Specificity of human lymphocytes primed against allogeneic cells in vitro. 1. Optimalization of culture conditions for detection of HLA--D specificity

The specificity of lymphocytes primed against allogeneic cells in vitro has been examined in order to find the optimal conditions for detection in the restimulating response of HLA--D specificity, as defined by homozygous cell typing. It was found that reducing the number of stimulating cells to less than the number of responding cells (ratio R/S = 4 : 1) in the priming culture, and increasing the number of stimulating cells at restimulation gave better discrimination. Priming with HLA--D heterozygous stimulating cells, where the responding and stimulating cells shared the other HLA--D determinant, rendered the primed cells somewhat more discriminatory than priming with HLA--D homozygous cells. The optimal length of the secondary culture was found to be about 38 h.

In vitro mitogen stimulation of synovial fluid lymphocytes from rheumatoid arthritis and juvenile rheumatoid arthritis patients: dissociation between the response to antigens and polyclonal mitogens

The in vitro responses to mitogens of synovial fluid lymphocytes obtained from eight patients with rheumatoid arthritis (RA) and eight patients with juvenile rheumatoid arthritis (JRA) were studied. The results were compared to the transformation of the patient's peripheral blood lymphocytes stimulated with the same mitogens. Both RA and JRA synovial fluid lymphocytes showed a low transformation to the polyclonal mitogens PHA and PWM with a low ratio PHA-response/PWM-response. The stimulatory effect of purified protein derivative of tuberculin (PPD) was high, whereas a Candida albicans antigen preparation gave a more variable stimulation of the synovial fluid lymphocytes. In some patients the complete mitogen transformation profile of lymphocytes obtained from synovial fluid, synovial tissue and peripheral blood was studied. The results of the synovial fluid and tissue lymphocytes were similar.

Responses of alloantigen-primed lymphocytes in vitro. The contribution of increased frequencies of responding lymphocytes to differences between reactivity of normal and primed lymphocyte populations

Sensitization of lymphocytes against allogeneic cells in vitro results in significant enrichment of alloreactive lymphocytes. Such enrichment was found to profoundly influence the conditions for measuring proliferative responses. Fewer primed lymphocytes than unprimed ones had to be cultured to favor optimal proliferation. Second, proliferative responses could be detected using 10 to 20 times fewer primed responding cells than when using unprimed responders. Finally, although responses of both unprimed and primed lymphocytes were dependent on the number of stimulator cells in culture, the primary mechanism(s) through which this dependence was expressed appeared to differ. The results demonstrate that, under the same conditions, comparisons of responses of two populations that contain different proportions of reactive lymphocytes may not be justified.

In vitro secondary mixed leukocyte reaction (MLR). II. Interaction MLR determinants expressed by F1 cells

T cells from strain A primed in vitro to (C57BL/6 x A/JF1 [(B6 x A)F1] cells respond better to restimulation by (B6 x A)F1 than by B6 or a 1:1 mixture of A and B6 cells. The increase in the response to F1 cells is specific and due to MLR determinants present on (B6 x A)F1 cells but not on either of the parental cell types. (B6 x A)F1 cells express more than one F1-specific MLR determinant, and this expression is dependent upon products of alleles of at least two loci within the major histocompatibility complex (MHC). Responsiveness to these F1-MLR determinants is apparently controlled by more than one locus within the MHC.

Linear density gradient separation of human lymphocyte subsets. I. Analysis by mixed leukocyte culture and cell-mediated lympholysis responses

Linear density gradients were used to separate either unsensitized human peripheral blood lymphocytes or cells sensitized in mixed leukocyte culture (MLC), at different time points in the immune response. Testing of cells from the various density fractions for their ability to respond in MLC and cell-mediated lympholysis (CML) revealed that (a) activity between individual fractions differed, as well as activity between individual fractions and a suspension of unfractionated cells, (b) although precursor cells of MLC and CML were maximally enriched in closely associated light density regions, their respective distribution profiles were strikingly different, and (c) the density of cells responding in MLC and CML differed depending upon the point of the immune response at which the cells were separated. Whereas effector cells were of light density relative to the precursor cells, putative memory cells for CML exhibited a high density.

Responses of alloantigen-primed lymphocytes in vitro. The specificity of secondary responses assayed by titration of primed lymphocyte populations

Maximal proliferative responses were observed at lower responder cell densities in alloantigen-primed lymphocyte populations when restimulated with the specific priming cell than when restimulated with other allogeneic cells. This relationship was due to the larger number of lymphocytes within the primed population which responded to the specific sensitizing cell than to unrelated stimulator cells. As a result, at high responder cell densities, stimulator cells unrelated to the specific sensitizing cells elicited a disproportionately high response relative to the response stimulated by the specific cells. Restimulation of decreasing numpacity of different cells. Because primed populations contain a larger number of lymphocytes that responde to the specific stimulator than to other stimulators, responses of primed lymphocytes could be made operationally monospecific. Limiting dilution analysis demonstrated that low numbers of primed cells were stimulated by the specific sensitizing cells but not by unrelated stimulator cells.

In vitro generation of primary and secondary cytotoxic cell-mediated immune responses to chemically induced mouse sarcomas

Mixtures of lymph node and spleen cells from normal (untreated) BALB/c mice and from BALB/c mice whose syngeneic tumors had been excised 7-28 days previously ("tumor-excised mice"), were sensitized in vitro by cultivation for 9 days with cells from syngeneic, methylcholanthrene-induced sarcomas. The in vitro-sensitized lymphoid cells were tested in a 36-h microcytotoxicity assay for reactivity against target cells carrying the sensitizing tumor antigens, as well as against control target cells lacking these antigens. After co-cultivation with tumor cells, lymphoid cells from both normal and tumor-excised mice were cytotoxic to tumor cells carrying the sensitizing antigens. The cytotoxicity was generally specific, and occurred at low effector: target cell ratios (in some experiments down to 1:1). When lymphoid cells from tumor-excised mice were exposed in vitro for 9 days to cells carrying the same antigens as those which were originally present on the surgical excised tumors, the effector cells obtained gave a dose-dependent cytotoxic response suggestive of a linear relationship. When lymphoid cells from normal mice were similarly sensitized for 9 days, specifically cytotoxic lymphoid cells were generated but no linear dose-dependent response was detected.

Specific elimination of cytotoxic effector cells. I. Adsorptive behavior of effectors and their precursors and spleen cell monolayers

Monolayers formed of normal mouse spleen cells attached to polystyrene coated with poly-L-lysine were tested for their ability to bind specifically antigen-reactive cells in normal or primed mouse spleen. 88 to greater than 98% of the activity of cytotoxic populations was removed by a single adsorption. However, normal spleen cells or spleen cells previously primed in vitro could not be depleted of their capacity to be sensitized, even when adsorption effectively removed all residual cytotoxic activity from the same previously primed population. In fact, exposure to an immunoadsorbent augmented the ultimate cytotoxicity generated in a nonspecific fashion. This augmentation was especially dramatic in the case of a previously primed population and may have reflected the removal of a nonspecific suppressor. If antigen-reactive precursors cannot be removed efficiently by adsorption, other approaches to the generation of tolerant lymphoid populations, such as specific suppression of precursor differentiation must be sought.

Typing for HLA-D determinants. comparison of typing results using homozygous stimulating cells and primed cultures

Typing for HLA-D determinants, using primed lymphocyte typing (PLT), has been compared to the results obtained using conventional homozygous stimulating cell primary MLC tests. The HLA-Dwl, -Dw2 and -Dw3 specificities were studied. Preliminary results indicate that these two methods essentially type for the HLA-D determinants and that reproducible results can be obtained employing the PLT technique after 24 hours of incubation in the secondary cultures.

Dual pathway of B lymphocyte differentiation in vitro

Direct visualization of the events resulting from LPS stimulation of mouse spleen cells in vitro was achieved by characterizing the cells during four days of culture for morphology, Ig and theta surface markers and autoradiography after [3H] thymidine uptake. The changes observed were related to biochemical parameters such as incorporation of [3H] thymidine into DNA, Ig biosynthesis and secretion. Two pathways of B lymphocyte differentiation were observed: a) the generation of a large number of small B lymphocytes with high density of surface Ig but no internal pool detectable by immunofluorescence, and b) the maturation of a very small proportion of cells with a large intracellular pool and the ability to secrete Ig. Both cell types arise from dividing blast cells, either physically separated or traced by pulse chase experiments with [3H] thymidine. We discuss whether this duality is caused by the triggering of different B cell subpopulations at different developmental stages, preprogramed to one or the other pathway or whether the final direction of development depends on the microenvironment of individual dividing cells.

Generation of T memory cells in one-way mixed lymphocyte culture. IV. Primary and secondary responses to soluble and insoluble membrane preparations and to ultraviolet-light-inactivated stimulator cells

Neither normal CBA (H-2k) nor purified spleen T cells respond in vitro to soluble or insoluble membrane preparations or to ultraviolet-light-inactivated stimulator cells of the allogeneic DBA/2 (H-2d) strain. However, CBA spleen cells deprived of phagocytic cells show a slight proliferative response under these conditions. After being primed against mitomycin-blocked DBA/2 cells in one-way mixed lymphocyte culture, the secondary blast-derived T 'memory' cells display a good secondary blast (proliferative) response to both membrane antigens and to ultraviolet-light-inactivated stimulator cells. In addition to this, the secondary T lymphocytes--in contrast to nonprimed T cells--respond by cytotoxicity when ultraviolet-light-inactivated cells are used as the second stimulant.

Separation of T cell subpopulations capable of DNA synthesis, lymphotoxin release, and regulation of antigen and phytohemagglutinin responses on the basis of density and adherence properties

T memory cells specifically responsive to ovalbumin and performing the diverse functions of DNA synthesis, lymphotoxin release, and regulation can be isolated in enriched numbers in the most buoyant fractions (A+B) of bovine serum albumin gradients on day 9 after sensitization. At least 20-30% of these cells are capable of mounting a blastogenic response to ovalbumin. A+B cells responding to ovalbumin with DNA synthesis have adherent properties and are further enriched on passage through glass wool. The subpopulations capable of entering into blastogenesis and DNA synthesis and of lymphotoxin release are unresponsive to T mitogens. A+B cells are capable of either potentiating or suppressing DNA synthetic responses to both phytohemagglutinin and antigen when added to 5 X 10(5) D cells in different proportions. Potentiation or suppression of phytohemagglutinin responses were observed with 1 X 10(5) A+B cells, and total suppression was observed with A+B in the range of 4 X 10(3) to 2 X 10(4). The response to antigen was sometimes inhibited in the same cell combinations that gave a potentiated response to phytohemagglutinin and vice versa. Regulatory cells in this system were not macrophages since their effect was not mimicked by addition of peritoneal macrophages, and ablation of macrophages by carrageenan affected neither the potentiation nor suppression.

Long-term maintenance in vitro of human T cells by repeated exposure to the same stimulator cells. Differences when using repeated stimulation in allogeneic mixed leukocyte culture and when using stimulation with autologous lymphoblastoid cells

Cells from one-way human mixed leukocyte cultures (MLC) which had reverted to small lymphocytes after 2 weeks' incubation responded with accelerated kinetics and higher thymidine incorporation on restimulation with lymphocytes or lymphoblastoid cell line (LCL) cells having relevant antigens. In contrast to fresh lymphocytes, they did not respond to autologous LCL cells. Cultures could be restimulated every second week with relevant allogeneic lymphocytes and could thus be maintained for periods of up to 4 months. Almost all these cultured cells had T-cell characteristics, during stimulation as well as in their reverted phase. The response to phytohemagglutinin (PHA) successively disappeared with repeated allogeneic restimulation, whereas the response to the relevant lymphocytes and cells of related donors was maintained. When lymphocytes had been stimulated with autologous LCL cells, the restimulation response was accelerated, although lower than after the primary stimulation. Restimulated cultures could not be maintained by further restimulation. Allogeneic and autologous LCL were equally efficient restumulators. A low level of stimulation was also achieved with allogeneic lymphocytes. The PHA response was usually reduced.

Secondary responses of human lymphocytes to alloantigens in vitro

The secondary response of human lymphocytes following restimulation with alloantigens has been studied. If fresh stimulating cells are added to a mixed leukocyte culture (MLC) at a time when the peak of proliferative and cytotoxic activity has passed, a rapid reactivation occurs. The secondary response in MLC demonstrates specificity such that restimulation with the original sensitizing cell (or one presumably sharing the LD genetic determinants responsible for triggering MLC) induces a greater proliferative response than a third-party cell. On the other hand, the secondary cytotoxic response is directed towards the SD antigens of the original sensitizing cell regardless of which cell is used for restimulation. Possible mechanisms of cellular interactions are considered to explain these results.