Human post-thymic precursor cells in health and disease. IX. Immunoregulatory T cell circuits in peripheral blood of patients with rheumatoid arthritis

We studied T cell subpopulations and their immunoregulatory circuits in the peripheral blood of 16 patients with rheumatoid arthritis (RA) who were receiving no medications that might interfere with the results. We found normal T cells with receptors for the Fc portion of IgG or IgM as well as autologous rosette-forming T cells (Tar cells), a subpopulation of T cells we have found to have the properties of human post-thymic precursors. We also found that peripheral blood cells of RA patients have normal concanavalin A-induced or spontaneously-expanded suppressor cell functions. Also normal were the characteristic functions of the Tar cells; feedback inhibition and the generation of suppression. The normal state of these T cell subpopulations and immunoregulatory circuits in the peripheral blood of patients with RA contrasts with their various abnormalities in other connective tissue diseases. This may either mean that the immunoregulatory aberration in RA involves primarily B cells, or, if it involves T cells, that it does so primarily in the synovial membrane.

Human post-thymic precursor cells in health and disease. I. Characterization of the autologous rosette-forming T cells as post-thymic precursors

Human autologous-rosette-forming T cells (Tar cells) have many of the characteristics of post-thymic precursor cells. Thus, they bind to sheep erythrocytes but have neither receptors for the Fc portion of IgG nor for that of IgM. They include a subpopulation that binds peanut agglutinin which suggests that they are immature and, as opposed to T cells with either receptors for the FC portion of IgM (T mu) or of IgG (T gamma), Tar cells adhere to nylon wool, another possible indicator of immaturity, as is their extreme sensitivity to hydrocortisone both in vitro and in vivo. There are more Tar cells in cord blood than in the peripheral blood of young adults and there are more Tar cells in the peripheral blood of young adults than in the peripheral blood of elderly subjects. By co-culturing T mu and B cells, or T mu, or Tar and B cells in the presence of pokeweek mitogen (PWM) we were able to determine that these cells cause feedback inhibition, a function considered characteristic of post-thymic precursors. In co-cultures in which we placed mononuclear cells (MNC) or MNC plus Tar cells, or MNC depleted of Tar cells or MNC depleted of Tar cells plus Tar cells stimulated with PWM, we determined that Tar cells play a role in the generation of suppression thereby confirming that human Tar cells are precursor cells. We also found that Tar cells proliferated and generated T gamma and T mu cells both spontaneously and in greater numbers, under the effect of serum thymic factor.

HLA-DR antigens induce proliferation and cytotoxicity of T cells against haptenated (TNP and FITC) self structures

Antisera directed against the heavy, the light, or reactive against the complex of both chains of HLA-DR antigens strongly inhibited proliferation of T cells induced by TNP- or FITC-labeled autologous cells when added at initiation of the cultures, but not 72 h later. T cells from cultures treated with the anti-DR sera were unresponsive to interleukin-2 (IL-2). Nonetheless, the anti-DR sera did not inhibit proliferation of T cells that had already acquired sensitivity to IL-2. The DR antibodies abrogated the synthesis of IL-2 induced by both TNP-and FITC-conjugated autologous cells. Treatment of TNP-and FITC-labeled autologous cell cultures with the four different types of anti-DR sera significantly inhibited the induction of cytotoxic T cells. However, DR antibodies added at the effector phase of cytotoxicity assays did not inhibit the cytotoxic activity. Effector T cells from cultures treated with the anti-DR sera were unresponsive to IL-2 and addition of IL-2 to these cultures did not restore the cytotoxic activity. In contrast, effector T cells from cultures performed in the absence of the anti-DR sera proliferated to Il-2 stimulation and addition of IL-2 to these cultures significantly increased the generation of killer cells specific for hapten-labeled self structures. From these results we concluded the following: (1) Both the heavy and the light chains of Dr antigens participate actively in the activation of T cells by rendering resting T cells sensitive to IL-2 and by inducing production of the growth factor in TNP-and FITC-conjugated autologous cell cultures. (2) The heavy and light chains of the DR antigens play an essential role in the induction of cytotoxic T cells specific for hapten-labeled self structures, most likely by enabling cytotoxic T cells to respond to Il-2 and by inducing the IL-2 producer T cells to synthesize the growth factor.

Role of individual chains of HLA-DR antigens in activation of T cells induced by alloantigens

The role of HLA-DR antigens in the activation of T cells in the allogeneic mixed lymphocyte reaction (MLR) was studied by using antibodies raised against the alpha, beta or the complex of both chains of the HLA-DR antigens. Antisera directed against the alpha or the beta chain strongly inhibited the T-cell proliferative response when added at the beginning of MLR cultures but not 72 h later. T cells from MLR cultures treated with either alpha-chain- or beta-chain-specific antibodies did not respond to interleukin-2 (IL-2) by proliferating, whereas T cells from non-anti-DR-treated cultures showed a proliferative response to IL-2-stimulation. However, neither the anti-alpha chain nor the anti-beta chain serum was able to inhibit continuous proliferation of already activated, IL-2-reactive T cells supported by IL-2. In MLR, OKT4+ but not OKT8+ lymphocytes synthesized IL-2. This function was abrogated by the alpha-chain-specific antibody but not by the anti-beta chain serum. Interleukin-1 (IL-1) did not reverse the inhibitory activity on IL-2 synthesis of the alpha-chain antibody, while IL-1 promoted the production of IL-2 in MLR cultures not exposed to the anti-DR sera. In addition, nonstimulated OKT4+ cells were unresponsive to IL-1 and did not produce IL-2. From these results, it is concluded that HLA-DR antigens participate actively in the activation of T cells by allogeneic non-T cells. Thus, both the alpha and beta chains of HLA-DR antigens render resting T cells sensitive to IL-2. In addition, the alpha but not the beta chain participates in the production of IL-2 by enabling OKT4+ lymphocytes to respond to IL-1 and subsequently to synthesize IL-2. Once T cells have acquired responsiveness to IL-2 and this growth factor has been produced there is no further requirement for HLA-DR antigens. Continuous proliferation and growth of IL-2-reactive T cells depends on the availability of interleukin-2.

Autologous rosette-forming T cells as the responding cells in human autologous mixed-lymphocyte reaction

Autologous rosette-forming cells (Tar cells) have surface and functional characteristics of post-thymic precursors and among these characteristics there are some that have been identified in the responsive cell of the autologous mixed-lymphocyte reaction (AMLR). We therefore did AMLR with circulating mononuclear cells from normal subjects using as responding cells either total T cells, T cells depleted of Tar cells, or purified Tar cells. The response of Tar cells in AMLR was significantly greater than that of total T cells and these responded significantly more than Tar-depleted T cells. Conversely, Tar cells responded less than total T cells or T cells depleted of Tar cells in allogeneic mixed-lymphocyte reactions. Increasing numbers of Tar cells gave significantly greater AMLR responses both alone and when added to diminishing proportions of Tar-depleted T cells to keep the number of T cells constant in the system. Tar cells are the responding cells in AMLR but not in allogeneic mixed-lymphocyte reactions.

Heterogeneity of glutamine synthetase polypeptides in Neurospora crassa

Purified preparations of Neurospora crassa glutamine synthetase contain two nonidentical polypeptides that can be separated by acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and 7 M urea. These polypeptides are synthesized both in vivo and in a heterologous cell-free protein-synthesizing system. The data presented indicate that both polypeptides contain an active site for glutamine synthetase activity and suggest that there is not a precursor-product relationship between them.

Glutamine metabolism in nitrogen-starved conidia of Neurospora crassa

During nitrogen deprivation, de novo synthesis of glutamine synthetase was induced in non-growing conidia of Neurospora crassa. When ammonia or glutamine was added to conidia which had been deprived of nitrogen, glutamine and arginine accumulated at a higher rate than in condia not deprived of nitrogen. The degradation of exogenous glutamine to glutamate is apparently a necessary step in the accumulation of glutamine and arginine within the conidia. In non-growing conidia, a cycle probably operates in which glutamine is degraded and resynthesized. The advantages of such a cycle would be that the carbon and nitrogen could be used to synthesize amino acids in general, as well as for the synthesis and accumulation of arginine and/or glutamine in particular.

Immunochemical characterization of glutamine synthetase from Neurospora crassa glutamine auxotrophs

Glutamine synthetase derived from two Neurospora crassa glutamine auxotrophs was characterized. Previous genetic studies indicated that the mutations responsible for the glutamine auxotrophy are allelic and map in chromosome V. When measured in crude extracts, both mutant strains had lower glutamine synthetase specific activity than that found in the wild-type strain. The enzyme from both auxotrophs and the wild-type strain was partially purified from cultures grown on glutamine as the sole nitrogen source, and immunochemical studies were performed in crude extracts and purified fractions. Quantitative rocket immunoelectrophoresis indicated that the activity per enzyme molecule is lower in the mutants than in the wild-type strain; immunoelectrophoresis and immunochemical titration of enzyme activity demonstrated structural differences between the enzymes from both auxotrophs. On the other hand, the monomer of glutamine synthetase of both mutants was found to be of a molecular weight similar to that of the wild-type strain. These data indicate that the mutations are located in the structural gene of N. crassa glutamine synthetase.

[Congestive myocardiopathy and early dyastolic closure of the tricuspid valve. Report of a case with acute tricuspidization]

A case with congestive cardiomiopathy and early diastolic closure of the tricuspid valve is presented. This abnormal echocardiographic finding was probably the result of severe tricuspid regurgitation occurring in a restricted right ventricle. The absence of paradoxical septum was determinedly the left ventricular pathology. In this case, echocardiography was more sensitive for the detection of the left sided abnormalities, than the heart cath data.

Nitrogen source regulates glutamine synthetase mRNA levels in Neurospora crassa

Neurospora crassa glutamine synthetase mRNA was measured by its capacity to direct the synthesis of the specific protein in a cell-free system derived from rabbit reticulocytes. N. crassa cultures grown on glutamate as the sole nitrogen source had higher mRNA activities than did those grown on glutamine. The differences were about 10-fold when polysomal RNA was used for translation and about 5-fold when either total cellular RNA or polyadenylic acid-enriched cellular RNA was used. These data indicate that in exponentially growing N. crassa, the nitrogen source regulates glutamine synthetase by adjusting specific mRNA levels.

Genetics and physiology of Neurospora crassa glutamine auxotrophs

This work reports on the isolation and characterization of two glutamine auxotrophs in Neurospora crassa. The mutations responsible for the glutamine-requiring phenotype were very closely linked, and one of them proved to be recessive to wild type. The mutations impaired the conversion of glutamic acid to glutamine and resulted in changes of both the activity and oligomeric structure of the enzyme glutamine synthetase.

Nitrogen regulation of glutamine synthetase in Neurospora crassa

A higher activity of glutamine synthetase (EC 6.3.1.2) was found in Neurospora crassa when NH4+ was limiting as nitrogen source than when glutamate was limiting. When glutamate, glutamine or NH4+ were in excess, a lower activity was found. Immunological titration and sucrose gradient sedimentation of the enzyme established that under all these conditions enzyme activity corresponded to enzyme concentration and that the octamer was the predominant oligomeric form. When N. crassa was shifted from nitrogen-limiting substrates to excess product as nitrogen source, the concentration of glutamine synthetase was adjusted with kinetics that closely followed dilution by growth. When grown on limiting amounts of glutamate, a lower oligomer was present in addition to the octameric form of the enzyme. When the culture was shifted to excess NH4+, glutamine accululated at a high rate; nevertheless, there was only a slow decrease in enzyme activity and no modification of the oligomeric pattern.

Neurospora crassa glutamine synthetase. Role of enzyme synthesis and degradation on the regulation of enzyme concentration during exponential growth

The specific activity of Neurospora crassa glutamine synthetase varies according to the nitrogen source in which the organism is grown. In a poor nitrogen source such as glutamate, the specific activity of the enzyme is higher than that found in good nitrogen sources such as ammonium or glutamine. These differences in specific enzyme activity correspond to differences in enzyme concentration. The relative rates of glutamine synthetase synthesis and degradation were measured in exponential cultures grown in different nitrogen sources. The differences in enzyme concentration are explained by differences in the relative rate of enzyme synthesis.

Neurospora crassa glutamine synthetase. Translation of specific messenger ribonucleic acid in a cell-free system derived from rabbit reticulocytes

The total reticulocyte lysate cell-free protein-synthesizing system was incubated in the presence of Neurospora crassa RNA. With the aid of an antibody directed against purified N. crassa glutamine synthetase, the synthesis of a specific protein was detected. This protein precipitates with antiglutamine synthetase using both direct and indirect procedures, migrates with the same molecular weight as the monomer of N. crassa glutamine synthetase when subjected to acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and chromatographs as N. crassa glutamine synthetase on anthranilate-bound Sepharose. These data indicate the translation of the mRNA that codes for N. crassa glutamine synthetase. This RNA behaves as poly(A)-containing material when fractionated on oly(U)-Sepha-rose.

Neurospora crassa glutamine synthetase. Purification by affinity chromatography and characterization of subunit structure

Neurospora crassa glutamine synthetase was purified to homogeneity by a procedure based on affinity chromatography. The enzyme is adsorbed to a matrix of anthranilic acid bound to Sepharose and eluted with AMP. Different experimental approaches indicate that the enzyme has an octameric structure formed by subunits of identical molecular weight.