Quantitative studies on T cell diversity. III. Limiting dilution analysis of precursor cells for T helper cells reactive to xenogeneic erythrocytes

"Doubt No More": Two Sizes Fit All

This Pillars of Immunology article is a commentary on “Differing lymphokine profiles of functional subsets of human CD4 and CD8 T cell clones,” a pivotal article written by P. Salgame, J. S. Abrams, C. Clayberger, H. Goldstein, J. Convit, R. L. Modlin, and B. R. Bloom, and published in Science, in 1991. https://www.science.org/doi/10.1126/science.254.5029.279.

Immunobiology of the critical asthma syndrome

It is now recognized that asthma incorporates a broad spectrum of syndromes with varying clinical manifestations. Future improvements in asthma treatment will require a clear characterization of these asthma phenotypes and the cellular mechanisms underlying these clinical manifestations. Herein, we will describe the current knowledge of asthma biology. This will include a review of the early pioneers in asthma and allergy, how this work led to our understanding of TH1 and TH2 cytokines, and the development of the "hygiene hypothesis." We will discuss the utility and limitations of the TH1-TH2 model of asthma in animal and human studies, and how this knowledge addresses controversies surrounding the hygiene hypothesis and other competing models. We will discuss novel therapies that have been developed based on mechanistic understanding of asthma pathobiology, including successes and shortcomings of these therapies. We will review the early work that led to the recognition of "asthma phenotypes." This will include the early discovery of various inflammatory subtypes in asthma and how these inflammatory subtypes correlate with response to therapy. Finally, we will describe recent discoveries in asthma biology that will include the role of the airway epithelium in asthma pathogenesis, novel cytokines important in asthma that may serve as novel therapeutic targets, and the identification of newly described innate immune cells and their role in asthma. Improved understanding of the complex biology underpinning the various asthma phenotypes is critical for our ability to optimize treatment for all patients that suffer from asthma and critical asthma syndromes.

Regulation by CD25+ lymphocytes of autoantigen-specific T-cell responses in Goodpasture's (anti-GBM) disease

BACKGROUND

Goodpasture's, or anti-glomerular basement membrane (GBM), disease is unusual among autoimmune diseases in that it rarely follows a relapsing-remitting course. Moreover, untreated, autoantibodies disappear spontaneously after 1 to 3 years and, following treatment, autoreactive T cells diminish in frequency. This suggests that operational tolerance toward the autoantigen is reestablished. However, the mechanisms underlying this have remained unclear. Recent data have suggested that a population of regulatory T lymphocytes can suppress both autoimmune and alloimmune responses in animal models and are present in normal individuals. However, to date, they have not been demonstrated to play a role in human renal autoimmune disease.

METHODS

We studied the role of regulatory CD25+ cells in suppressing T-cell responses to the Goodpasture autoantigen in nine patients with Goodpasture's disease.

RESULTS

At the time of acute presentation, there was no evidence of a regulatory cell population. However, from 3 months onward a population emerged, capable of suppressing the response to the Goodpasture autoantigen. Following depletion of CD25+ cells, the frequencies of autoreactive-, GBM-, or collagen alpha 3(IV)NC1-specific T cells were significantly increased (P = 0.031 by paired t test), with five of seven (71%) convalescent patients and no acute patients demonstrating regulation.

CONCLUSION

These data demonstrate that, in Goodpasture's disease, regulatory CD25+ T cells play a role in inhibiting the autoimmune response. Their emergence and persistence may underlie the "single hit" nature of this condition. Understanding the conditions required for the development and propagation of these cells would allow development of novel therapeutic strategies for inducing hyporesponsiveness in autoimmune disease.

Human CD4(+)CD25(+) cells: a naturally occurring population of regulatory T cells

Despite thymic deletion of cells with specificity for self-antigens, autoreactive T cells are readily detectable in the normal T-cell repertoire. In recent years, a population of CD4(+) T cells that constitutively express the interleukin-2 receptor-alpha chain, CD25, has been shown to play a pivotal role in the maintenance of self-tolerance in rodent models. This study investigated whether such a regulatory population exists in humans. A population of CD4(+)CD25(+) T cells, taken from the peripheral blood of healthy individuals and phenotypically distinct from recently activated CD4(+) T cells, was characterized. These cells were hyporesponsive to conventional T-cell stimuli and capable of suppressing the responses of CD4(+)CD25(-) T cells in vitro. Addition of exogenous interleukin-2 abrogated the hyporesponsiveness and suppressive effects of CD4(+)CD25(+) cells. Suppression required cell-to-cell contact but did not appear to be via the inhibition of antigen-presenting cells. In addition, there were marked changes in the expression of Notch pathway molecules and their downstream signaling products at the transcriptional level, specifically in CD4(+)CD25(+) cells, suggesting that this family of molecules plays a role in the regulatory function of CD4(+)CD25(+) cells. Cells with similar phenotype and function were detected in umbilical venous blood from healthy newborn infants. These results suggest that CD4(+)CD25(+) cells represent a population of regulatory T cells that arise during fetal life. Comparison with rodent CD4(+)CD25(+) cells suggests that this population may play a key role in the prevention of autoimmune diseases in humans.

Analysis of cellular interactions in limiting dilution cultures

Limiting dilution (LD) cultures are often used to study cellular heterogeneity in responses of murine splenocytes to specific or polyclonal activation. LD titration curves often reveal a nonlinear dependence of response on input cell dose. Although 'zigzag' shaped curves of this kind are often interpreted and analyzed as resulting from interactions among three distinct cell types, we observe that a more parsimonious two cell model, including a cell type that can generate both positive and negative effects, provides better fit to a wide range of experimental data. We have developed mathematical models for the accurate estimation of the frequencies of both interacting cell types and of the parameters for their multi-hit interaction. We show examples of LD cultures in which specific experimental manipulations alter the frequency of only one of the two cell types, or alter the interaction parameters without a change in responder frequency. We also provide a simplified method for approximation of the model parameters using graphical approaches and simple algebra. Lastly, we present an improved method for calculation of the effect generated per responder cell in microclonal cultures.

Effects of retinoids on regulatory cellular interactions in primary mixed lymphocyte reaction (MLR)

The effects of two retinoids, all-trans-retinoic acid and 13-cis-retinoic acid on murine splenic lymphocyte proliferative response in mixed culture were evaluated. In contrast with previously reported absence of retinoic acid (RA) effect on mixed lymphocyte reaction (MLR) the conditions for a strong potentiation of proliferative response of murine lymphocytes with RA were obtained. Stimulatory cells were determined to be the main targets for RA. The data suggest that the RA potentiating effect is the result of an increase in stimulator cell immunogenicity after their pre-treatment with RA before use in MLR. Optimal potentiation by retinoids of proliferative response was found at non-optimal conditions of mixed culture.

The B cell repertoire of patients with rheumatoid arthritis. Frequencies and specificities of peripheral blood B cells reacting with human IgG, human collagens, a mycobacterial heat shock protein and other antigens

Using a potent in vitro limiting dilution culture system, we have activated human peripheral blood B cells to proliferate and to differentiate into antibody-secreting cells (ASC). Under these conditions 25-100% of B cells are clonally expanded and produce IgM, IgG or IgA. Culture supernatants were tested for antibodies binding to human IgG-Fc fragments (RF), the 65-kD heat shock protein of Mycobacterium bovis (hsp60), human collagens type I, II, IV, V, transferrin, lactoferrin, albumins, and gelatine. All blood samples contained precursors of ASC (p-ASC) able to produce IgM binding to these antigens in frequencies above 0.03% of B cells. Most interestingly, a significant difference exists between rheumatoid arthritis (RA) patients and controls, concerning the relative frequencies of p-ASC able to produce monospecific or multireactive RF. Whereas most p-ASC(RF) in RA patients are monospecific (mean ratio 3.7), most p-ASC(RF) in healthy control persons are cross-reactive with at least one of five other antigens tested (mean ratio 0.2). The data suggest a disease-specific expansion of p-ASC committed to the production of monospecific rheumatoid factors.

Molecular detection and in vivo analysis of the specific T cell response to a protein antigen

We have analyzed in detail the repertoire of transcripts encoding the V beta chains of the T cell receptor and investigated the T cell response of B10.A mice to pigeon cytochrome c. We were thus able to follow the specific T cell response in vivo after immunization with this protein antigen. The response is first detectable in the draining lymph nodes, then in the spleen and in the blood. It is qualitatively similar in individual animals. It is dominated by a major category of specific T cells harboring a V beta 3-J beta 1.2 rearrangement, and a limited and well-defined set of nucleotide sequences, previously found in several specific T cell hybridomas and clones. This predominance is observed from the onset of the immune response strongly suggesting the notion that there is no variation and, therefore, no maturation of the T cell response in the course of immunization.

Immunologic tolerance in lymphatic filariasis. Diminished parasite-specific T and B lymphocyte precursor frequency in the microfilaremic state

To explore the mechanisms of antigen-specific immune unresponsiveness seen in microfilaremic patients with bancroftian filariasis, T and B cell precursor frequency analysis was performed using PBMC from individuals with either asymptomatic microfilaremia (MF, n = 7) or chronic lymphatic obstruction (CP, n = 20). Highly purified CD3+ cells were partially reconstituted with adherent cells and their proliferative response to parasite antigens determined in cultures of T cells by limiting dilution analysis. A filter immunoplaque assay also assessed the frequency of both total and parasite-specific Ig-producing B cells. While the lymphocyte proliferation to mitogens and to a nonparasite antigen (Streptolysin-O, [SLO]) were similar in all groups of patients, the frequency of parasite-specific CD3+ T cells was significantly lower (geometric mean [GM], 1/3,757) in MF patients when compared to that in CP patients (GM 1/1,513; P less than 0.001). Similarly, the proportion of lymphocytes producing parasite-specific IgE or IgG was significantly lower in MF patients (IgE mean, 0.2%; IgG mean, 0.33%) compared with CP patients (IgE mean, 3.2%; IgG mean, 1.76%; P less than 0.05 for both comparisons). These observations imply that low numbers of parasite-specific T and B lymphocytes may be partially responsible for the severely diminished capacity of lymphocytes from patients with MF to produce parasite-specific antibody and to proliferate to parasite antigen in vitro. Such differences in parasite-specific lymphocyte responses suggest that tolerance by clonal anergy may be a critical mechanism for maintaining the microfilaremic state.

Interleukin 2/interleukin 4-independent T helper cell generation during an in vitro antigenic stimulation of mouse spleen cells in the presence of cyclosporin A

Cyclosporin A (CsA), an immunosuppressive drug which completely suppresses the humoral response to thymus-dependent antigens, does not affect the generation of T helper (Th) cells during an in vitro stimulation of murine spleen cells with sheep red blood cells. The appearance of Th cells depends on time and their development can be prevented by X-ray irradiation performed at the onset of the culture and up to 3-4 days later; however, beyond this time, irradiation is ineffective, suggesting that cell proliferation is essentially completed by this time. The activity of Th cells generated in the presence of CsA is resistant to irradiation, indicating that the effector cells belong to a memory subset. Limiting dilution analysis has shown that the frequency of the Th cells recovered from 6-day sheep red blood cell-stimulated and CsA-treated cultures is of approximately 1.4 X 10(-3), representing an increment of about 500-fold compared to naive spleen cells. The increased frequency of Th cells and the sensitivity to irradiation of the generation of these cells demonstrate that Th cell precursors proliferate in the presence of CsA. Lymphokine genes transcription analysis confirms that the inhibition of interleukin (IL) 2/IL 4 gene expression is one target of CsA action. That the generation of Th memory cells can nevertheless take place strongly argues in favor of the existence of an IL 2/IL 4-independent pathway for murine T cell proliferation. Our finding that the transcription of the IL 7 gene is not inhibited by CsA raises the possibility for a role of this T cell growth factor in the generation of memory Th cells.

Evidence for mouse Th1- and Th2-like helper T cells in vivo. Selective reduction of Th1-like cells after total lymphoid irradiation

Purified CD4+ BALB/c spleen T cells obtained 4-6 wk after total lymphoid irradiation (TLI) helped normal syngeneic B cells to produce a vigorous antibody response to TNP keyhole limpet hemocyanin in adoptive cell transfer experiments. However, the same cells failed to transfer delayed-type hypersensitivity to the adoptive hosts as measured by a foot pad swelling assay. In addition, purified CD4+ cells from TLI-treated mice were unable to induce graft vs. host disease in lethally irradiated allogeneic C57BL/Ka recipient mice. In response to mitogen stimulation, unfractionated spleen cells obtained from TLI mice secreted normal levels of IL-4 and IL-5, but markedly reduced levels of IL-2 and INF-gamma. A total of 229 CD4+ clones from spleen cells of both normal and TLI-treated mice were established, and the cytokine secretion pattern from each clone was analyzed. The results demonstrate that the ratio of Th1- and Th2-like clones in the spleens of normal BALB/c mice is 1:0.6, whereas the ratio in TLI mice is approximately 1:7. These results suggest that Th2-like cells recover rapidly (at approximately 4-6 wk) after TLI treatment and account for the early return of antibody helper activity and secretion of IL-4 and IL-5, but Th1-like cells recover more slowly (in approximately 3 mo) after irradiation, and this accounts for the deficit in cell-mediated immunity and the reduced amount of IL-2 and IFN-gamma secretion.

Enumeration of viral antigen-reactive helper T lymphocytes in human peripheral blood by limiting dilution for analysis of viral antigen-reactive T-cell pools in virus-seropositive and virus-seronegative individuals

A limiting-dilution analysis technique was developed which enumerates human T cells with the capacity to secrete T-cell growth factors such as interleukin 2 after contact with herpes simplex virus type 1 (HSV-1) or cytomegalovirus (CMV) antigens (operationally defined as virus-reactive helper T cells [HTL]). By using this limiting-dilution analysis technique, the peripheral blood of HSV-seropositive individuals was analyzed for the frequency of HSV antigen-reactive HTL and for the ability either to proliferate or to secrete detectable T-cell growth factors in conventional HSV antigen-stimulated lymphocyte cultures. We found that the magnitudes of the latter two responses did not correlate directly with the frequency estimates of HSV antigen-reactive HTL. The study was expanded to analyze both HSV and CMV reactivities within individuals. Those who were seropositive for HSV or CMV were found to have relatively high HTL frequencies for the viral antigens to which they were sensitized. However, those who were seronegative for one of the viruses often had HTL reactive with that virus in their peripheral blood. These latter HTL frequencies were highly variable and ranged from undetectable to quite prominent, even within the same individual at different times. In general, it was found that viral antigen-reactive serologic activity does not necessarily reflect the status of viral antigen-reactive cell-mediated immunity in humans and that viral antigen-induced T-cell responses may be unexpectedly complex, rather than absent, in individuals who are seronegative for a particular virus.

Plasticity of T-cell function. II. Transient induction of CD8 (Ly-2) expression in cloned EL-4 lymphoma cells depending on cell density

EL-4 lymphoma cells are able to suppress the primary humoral immune response of spleen cells to sheep erythrocytes or 4-hydroxy-3-iodo-5-nitrophenylacetyl-keyhole limpet haemocyanin (NIP-KLH) in vitro. Typically, the cells suppress very efficiently in small numbers, but lose this capacity as the numbers increase. Three clones were analysed and this fluctuation in function was paralleled by a fluctuation in the expression of CD8 (Ly-2). Clones were incubated for 2 days, starting from different seeding concentrations, and analysed with cytofluorography. Neither Thy-1 nor CD5 (Ly-1), H-2 K, H-2 D, LFA-1 (all positive) nor CD4 (L3T4) or MEL-14 (both negative) were influenced by this treatment. In contrast, cells were CD8- at high seeding concentrations, and CD8+ at low seeding concentrations. When cell cultures grew to higher densities, the cells again lost the capacity to express CD8. Experiments testing the suppressive capacity of individual EL-4 clones after preculture at different densities or in the presence of antibodies against CD8 suggest that the efficiency of suppression may well be correlated to the amount of CD8 expressed.

Frequencies and interactions of regulatory T cells. I. The balance between help and suppression regulates the primary immune response to keyhole limpet hemocyanin in vitro

Frequencies and efficiencies of regulatory T cells from non-immunized mice were estimated in several assay systems differing from each other in cellular composition and antigen dose (NIP-KLH). The NIP-specific and total IgM responses were quantified. Using 10(4) syngeneic B cells and 50 micrograms/ml NIP-KLH, helper (Th) cells from 5 day immune donors were detected in frequencies of 1:3000-1:4000 in lymphnode and spleen T cells, with an efficiency of 70-90 ng IgM/Th cell in C57B1/6 mice. In non-immune spleen T cells, Th cells were observed in frequencies of 1:16,000-1:38,000, with comparable efficiency, but these Th cells appeared suppressed at increased T cell doses. Polyclonal activation led to the appearance of multiple independently regulated populations of Th cells with similar efficiencies. In the presence of 10(5) syngeneic spleen cells, treated once with anti-Thy-1 antibody and complement and 50 micrograms/ml NIP-KLH, suppressor activity was observed in the same T cell population. Similar to help, suppression fluctuated with increasing T cell numbers. Using 1 x 10(6) spleen cells and 50 micrograms/ml NIP-KLH as assay system, T cells enhanced the responses. Again, several independently regulated populations were observed, with efficiencies slightly higher than those of the above-described Th cells. By maintaining the cellular components of the assay system constant (10(4) B cells) and titrating the antigen, Th cell frequencies showed little variation up to 100 micrograms/ml NIP-KLH and were always suppressed at higher T cell numbers. At 200 micrograms/ml NIP-KLH, the frequency was increased to approximately 1:2000, and not suppressed, i.e., was identical to the frequency observed in mice immunized 5 days previously. Efficiencies increased with increasing doses of antigen. The results strongly indicate that regulatory T cell function shows "plasticity", in the sense that the appearance and the frequencies of helping and suppressing T cell populations highly depend on the micro-environment present in culture.

Autoreactive T cells in rheumatic disease (1). Analysis of growth frequencies and autoreactivity of T cells in patients with rheumatoid arthritis and Lyme disease

A limiting dilution system was established in order to estimate frequencies of interleukin-2 (IL-2)-responsive, autoreactive and alloreactive T cells in samples of peripheral blood (PBL) and synovial fluid lymphocytes (SFL), from patients with rheumatoid arthritis (RA) and lyme disease, as well as from healthy donors and a patient with osteoarthrosis. The frequencies of IL-2-dependent T-cell colony formation were significantly higher in patients with RA and lyme disease (median: 1/287) as compared to controls (median: 1/1,313) indicating a preactivation of T cells in these patients in vivo. Autoreactivity was measured by the proliferative response of T-cell lines to autologous irradiated PBL as stimulating cells. The frequencies of autoreactive T cells in blood were significantly higher in patients (median: 1/2,615) as compared to controls (median: 1/19,607). There was no significant difference in autoreactive T-cell frequencies between the patients' SFL (median: 1/3,185) and PBL (median: 1/2,615). In every case the frequency of alloreactive T cells exceeded the frequency of autoreactive T cells. Most autoreactive T-cell lines were also alloreactive and were shown to be MHC Class II-restricted. There is evidence of a down regulation of autoreactive T cells by suppressor cells in peripheral blood in two cases with elevated autoreactive T-cell frequencies (one RA patient and one control patient suffering from a viral infection). In contrast, no suppression of autoreactive T cells was observed in the RA patients' SFL or in PBL and SFL from patients with lyme disease. These results suggest that the chronic inflammation observed in RA and lyme disease may be supported by an elevated number of autoreactive T cells in the absence of suppressive mechanisms.

Limiting dilution analysis of the frequencies of helper and suppressor T cells in untreated and TNP-treated BALB/c mice: response as a consequence of perturbation of a stable steady state

B-cell response and suppression of response were analysed with respect to changes in frequency or composition of regulatory elements in comparison to untreated BALB/c mice. As antigenic stimulus the hapten TNP was used. Suppression was induced by intravenous (i.v.) injection of TNP-haptenized syngeneic lymphocytes; for inducing response, mice received TNP-horse red blood cells (HRBC). As the read-out system, plaque-forming cells (PFC) were determined after either the addition of naive B cells only [determination of the frequency of helper T-cells (TH)], or the addition of naive B cells plus saturating doses of TNP-specific TH [determination of the frequency of suppressor T-cells (Ts)]. The data indicate that, in untreated animals, a network of help and suppression is pre-existing, wherein TH are more frequent (1/1471) than TS (1/4413), but TS are dominant, i.e. when the fraction of non-responding cultures (F0) (determination of help) was plotted, an inversion of the curve was seen at high numbers of cells per well; however, the fractions of responding cultures (F+) (determination of suppression) could be plotted on a straight line. Application of antigen in suppressogenic or immunogenic form resulted in a two- to four-fold increase in the corresponding regulatory population but, concomitantly, a minor increase in the frequency of the mutual counteracting population was observed. Irrespective of any immunization schedule, TH were more frequent than TS. The overall shape of the 'helper' and 'suppressor' curves with spleen cells (SC) from suppressed mice resembled--besides changes in the frequencies--those obtained with SC of untreated animals. This corresponds to the maintenance of a state of unresponsiveness as in untreated animals. However, when SC from primed or suppressed plus primed mice were analysed, a different type of curve was obtained. Suppressor curves no longer followed a ratio dominance model; instead, at high numbers of cells per well, the frequency of wells with suppressive activity decreased. Correspondingly, in helper curves, a second slope of increasing numbers of wells with helper activity was seen at a high input of cells. Hence, response cannot be explained solely by expansion/activation of TH, but obviously a third regulatory population is involved which could not be detected in untreated animals. This third regulatory population could either be non-suppressible TH or--more likely, as will be discussed--contrasuppressor cells.

Cluster formation in a symmetrical network: a dynamical system for the description of the suppression among non-immune T lymphocytes and its application to the effects of immunization

A mathematical model has been developed for the description of the suppressive regulation between polyclonally activated normal and immune T cells. The model assumes reversible cell-cell interactions to interpret results from limiting dilution experiments performed to determine the frequencies of precursor cells for antigen-specific T effector lymphocytes and to analyse mechanisms regulating the maturation of precursor into effector T cells. In particular, the model deals with the changes induced in the T lymphocytes population following immunization with antigens. In these limiting dilution experiments, T cells are placed in cultures at varying cell numbers with all other essential culture constituents kept in excess. After polyclonal activation of the T cells in culture they are supplied with growth and maturation factors so that they form daughter clones of functionally active T effector cells. The typical result observed was that effector T cells develop in cultures at low cell input but that this development is totally suppressed at high cell numbers. This result suggested that, at high cell numbers, the effector T cells are exposed to a sufficient number of other T cells of appropriate specificity to permit suppressive interactions. Whereas this is the case for non-immune T cells, T cells after immunization develop into effector cells both at high as well as at low cell concentrations, though with efficiencies less than proportional to their number of precursors. Our mathematical model is made up of a set of first order autonomous ordinary differential equations in many variables permitting the calculations of numbers of free cells and of cells engaged in cellular clusters of varying sizes. Free cells can develop into effector cells whereas cells engaged in clusters cannot. We calculate the consequences of several reasonable hypotheses concerning the effects of immunization. We consider the possibility that immunization modifies the growth behavior of the antigen-specific cells to permit an increased or accelerated clonal expansion in culture. Alternatively, we consider the possibility that immunization changes the interaction strength between cells specific for the immunizing antigen and other cells. Thirdly, we have connected both behaviors by calculating the case of an inverse relationship between growth rates and intensities of interaction between cells. Our model has been inspired by the symmetrical network model and can be interpreted in this framework. It proposes that immune regulation is a consequence of idiotype-anti-idiotype interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic control of B cell function. III. IgVH-controlled polymorphism in the frequencies of B cells that recognize xenogeneic red blood cells

Previous work has shown that the primary IgM plaque-forming cell response of inbred mice to xenogeneic red blood cells (RBC) including sheep, horse and chicken RBC is under the control of two polymorphic genes or sets of genes, one linked to the Igh linkage group and the other of unknown linkage but unlinked to H-2 and a variety of other known genetic markers. Both genes together control B cell function but do not influence the function of T cells and macrophages. Thus, this system permits the study of two polymorphic loci that control B cell responsiveness. In this study we analyze the role of the Igh region in further detail. In bulk cultures and limiting dilution experiments, we confirm its exclusive influence on B cells also when analyzed separately from the background gene, i.e. in Igh-congenic strains. Moreover, we find in the majority of experiments 4-5-fold differences in sheep RBC-specific B cell precursor frequencies among lipopolysaccharide-reactive cells from 3 pairs of Igh-congenic high and low-responder strains. Similar frequency differences exist for horse RBC and chicken RBC-specific B cells but not for B cells with specificity for (4-hydroxy-5-iodo-3-nitrophenyl)acetyl (NIP)-gelatine. These differences are independent of the frequencies of B cells responding to lipopolysaccharide which are shown to be equal between Igh-congenic pairs of strains. Since the differences in RBC-specific B cell frequencies closely resemble the differences in bulk culture responses to the corresponding RBC, we conclude that the role of the Igh linkage group in controlling responsiveness to RBC lies in a selective influence on the B cell repertoire concerning precursor cells for RBC specificity. In addition, we find that the VH part of Igh is responsible for the observed frequency differences, suggesting that VH germ-line genes directly influence the composition of the mature B cell repertoire.

Structure, expression and divergence of T-cell receptor beta-chain variable regions

Analysis of three new T-cell receptor beta-chain variable regions together with those in the literature indicates that they have both remarkable similarities and differences with those of immunoglobulin. Less than 10 V regions appear to predominate in the thymus. V beta sequences are much more heterogeneous at the amino acid level than are immunoglobulin V regions and they appear to diverge between species much more quickly, apparently the result of additional hypervariable regions. Three of these putative new hypervariable regions lie outside of the classical immunoglobulin binding site, an indication that important interactions may be occurring in these regions with polymorphic MHC determinants.

The growth of concanavalin-A activated, Lyt selected subsets in IL-2 containing supernatants

The growth properties of Con A activated, Lyt selected splenic T lymphocytes were examined by limiting dilution analysis and clonally by single cell picking. Under the conditions used, a comparable frequency of Lyt 1+ and Lyt 2+ cells grew after Con A activation in the presence of Con A rat spleen supernatant. At a clonal level, however, the growth of these subsets differed qualitatively and quantitatively. While Lyt 2+ cells obtained clone sizes of several hundred cells, Lyt 1+ clone sizes were usually less than 100 cells, and many clones aborted their growth after a few days. Morphologically, the Lyt 1+ cell was smaller and usually showed fewer pseudopodial protusions as compared to the Lyt 2+ cell.

Differential expression of the repertoire in in vitro and in vivo responses to minor alloantigens

The response to multiple minor alloantigens in the secondary mixed lymphocyte culture (MLC) between mouse strains that are identical at the major histocompatibility complex (MHC) generally yields effector cytotoxic T lymphocytes (CTL) which show cross-reactive killing of most or all third-party mouse strains which also share MHC haplotypes. We have investigated the clonal diversity of CTL responses in vivo versus in vitro by examination of such cross-reactions, using CTL effector cells derived from a primary response, an in vivo secondary response, and an in vitro secondary MLC. CTL from these three responses were assayed on a panel of H-2k targets. Restimulation of antigen-primed spleen cells in vitro yielded CTL which were strongly cross-reactive on all targets, whereas the in vivo responses were much less so. We conclude that the set of clones which become cytotoxic effectors in vivo is much less diverse than the set which is primed on a first encounter with antigen and that powerful constraints must therefore operate on the specificity of in vivo responses to non-MHC antigens.

Cytotoxic T-cell precursors revealed in neonatally tolerant mice

Induction of neonatal tolerance leads to a profound reduction in cytotoxic T-lymphocyte precursor frequencies against the tolerated alloantigen ("tolerogen") as evaluated by limiting-dilution analysis. The curves obtained were linear within the range tested and, thus, did not yield evidence for any dissociation of cytotoxic precursors from regulatory cell populations. However, it could be shown that cytotoxic T-lymphocyte precursor frequencies against the tolerogen increased drastically if the tolerant spleen cells were adsorbed, prior to limiting-dilution culture, on monolayers of syngeneic blasts expressing receptors for the tolerogen but not if they were adsorbed on syngeneic blasts against third-party antigens. This finding implies that cytotoxic precursor cells against the tolerogen are not clonally deleted in tolerant animals but rather are suppressed by a regulatory cell population that is present at high frequency and presumably acts in an anti-idiotypic fashion.

Precursor frequency of antigen-specific T cells: effects of sensitization in vivo and in vitro

Limiting dilution analysis (LDA) of primary lymphocyte cultures was used to determine the frequency of keyhole limpet hemocyanin (KLH)-specific precursors in the peripheral blood of unimmunized individuals. The KLH-specific precursor frequencies ranged from 1:150,000 to 1:340,000. In contrast, frequencies of KLH-specific cells in the blood from immune donors ranged from 1:25,000 to 1:42,000. LDA of KLH-stimulated primary cultures indicated that the frequency of KLH-specific cells increased with time in culture reaching a four- to fivefold expansion relative to the frequency obtained prior to culture. The data presented suggest that the enhanced kinetics of secondary T-cell responses observed after in vitro sensitization are due to a decrease in the proportion of lymphocytes which exhibit a suppressor phenotype.

Quantitative studies on T cell diversity. IV. Mathematical analysis of multiple limiting populations of effector and suppressor T cells

Limiting dilution (LD) analyses of polyclonally activated T cells yielded results suggesting the existence of multiple paired populations of effector and suppressor precursors for a number of different T cell functions and specificities analyzed. These populations occur at graded frequencies and suppression occurs within a pair but not between pairs. In this paper, we establish the mathematical basis for the interpretation of these multi-component limiting dilution results. First, we derive equations for a number of mathematical models and identify one model that both makes biological sense and can be used to reproduce experimental data. Second, within this model, we identify parameters such as the frequency of suppressive cells and the number of suppressive cells required for suppression. The results suggest that within each paired population, suppressor precursors are 20 times more frequent that effector precursors. Furthermore, a similar but variable excess of suppressor cells is required for suppression to become effective. Together with the high frequency (1/50-1/500) of most effector T cell precursors previously reported, the results suggest that up to 40% of the T cells can become involved in suppression of an antigen-specific effector T cell population. These studies may provide exact estimates for predictions to be tested in experiments on immune regulation.