Isolation of a polypeptide that has lymphocyte-differentiating properties and is probably represented universally in living cells

ATP serves two distinct roles in protein degradation in reticulocytes, one requiring and one independent of ubiquitin

Protein degradation in rabbit reticulocytes is a nonlysosomal process requiring ATP. Recently, appreciable evidence has been presented that ATP is required for the covalent binding of the polypeptide ubiquitin to epsilon-amino groups on protein substrates. To test whether linkage of ubiquitin to substrates is required for ATP-dependent proteolysis, the amino groups of 3H-methyl-casein and denatured 125I-bovine serum albumin (BSA) were completely (93-99%) blocked by methylation, acetylation, carbamylation, or succinylation. In each case, the proteins lacking amino groups were still degraded by an ATP-stimulated process, although these various treatments altered absolute rates of proteolysis and reduced the magnitude of the ATP stimulation (two- to fourfold) below that seen measured with the unmodified substrates. When ubiquitin was removed by ion exchange chromatography, ATP still stimulated breakdown of casein and carbamylated casein twofold. The addition of ubiquitin in the presence of ATP caused a further twofold increase in the hydrolysis of unmodified casein but did not affect the degradation of casein lacking amino groups. Thus ubiquitin conjugation to substrates appears important in the breakdown of certain substrates (especially of BSA), but this reaction is not essential for ATP-stimulated proteolysis. The ATP-activated step that is independent of ubiquitin probably is also involved in the degradation of unblocked proteins, since both processes require Mg++ and ATP hydrolysis and are inhibited by hemin but not by protoporphyrin IX. These results suggest that ATP has distinct roles at different steps in the degradative pathway.

Committed precursors of B and T lymphocytes in chick embryo bursa of Fabricius, thymus, and bone marrow

Lymphocyte precursors in bursa of Fabricius, thymus and bone marrow (BM) of chick embryos were studied at different stages of incubation over 12-21 days, and for their state of commitment to B or T cell lines of development. Cell suspensions were fractionated on albumin gradients to remove nonlymphoid cells and incubated in vitro with bursopoietin, a specific inducer of B cells, or crude chicken thymus extract, a specific inducer of T cells, or ubiquitin, a nonspecific inducer. Precursors were identified by increases in numbers of cells bearing surface alloantigens as determined by immunofluorescence, either Bu-1 (specific to B cells) or Th-1 (specific to T cells). Precursors inducible to Bu-1+ cells were found in bursal cells and BM cells from all age groups but not in thymic cells. Precursors inducible to Th-1+ cells were found in thymic preparations and BM cells at all ages, but in significant numbers in bursa on day 12 only. Because B and T precursors were never found together in bursa or thymus, or only in very unequal amounts, it was concluded that precursors in these organs were not multipotential but were separately committed to one or other line of development. This argument did not apply to BM cells, for which other evidence was obtained. Bu-1+ cells were specifically induced in BM cells with bursopoietin and then removed by complement-dependent cytolysis wih anti-Bu-1 antiserum. When the remaining cells were incubated with ubiquitin, only Th-1+ cells were induced, showing that Bu-1 and Th-1 precursors were separately committed. Surface IgM was never induced on either bursal or BM lymphocytes. The Ia (or B-L) antigen was inducible on 12- to 21-day bursal cells, but could not be generated on BM cells until day 14 onwards. The pattern of occurrence of committed lymphocyte precursors in the developing chick embryo suggests that these cells are released into the circulation from both central lymphoid organs at their respective times of high lymphopoietic activity, and accumulate in the BM at least up to the time of hatching. Moreover, the presence of committed B precursors in bursa and committed T precursors in thymus at times and in quantities appropriate to the known features of avian lymphopoiesis leads us to conclude that in vitro induction is analogous to a true stage of in vivo B and T cell differentiation.

Decrease in uH2A (protein A24) of a mouse temperature-sensitive mutant

ts85 cell is a temperature-sensitive mutant of cell cycle, and chromosomal protein uH2A of this mutant disappears at the non-permissive temperature. uH2A in nucleosomes is thought to be synthesized or degradated as follows. H2A + Ubiquitin in equilibrium uH2A. Up to date, the degradation of uH2A was shown to be catalyzed by uH2A lyase, however no enzymes (factors) concerning its synthesis have been elucidated. Here, we show that ATP is prerequisite for the synthesis of uH2A, and that the disappearance of uH2A at the non-permissive temperature may be due to a reduction in the rate of synthesis rather than an increase in the rate of its degradation.

Conjugation of ubiquitin to denatured hemoglobin is proportional to the rate of hemoglobin degradation in HeLa cells

Ubiquitin was radioiodinated and introduced into HeLa cells by the erythrocyte-mediated fusion procedure. Fractionation of injected HeLa cells and subsequent NaDodSO4/polyacrylamide gel electrophoresis showed that HeLa nuclei contained two major labeled proteins: ubiquitin and the histone H2A-ubiquitin conjugate, protein A24. HeLa cytosol contained ubiquitin and a series of ubiquitin-protein conjugates of diverse molecular weights. When injected HeLa cells were treated with phenylhydrazine to denature the cotransferred hemoglobin, a series of prominent ubiquitin-globin conjugates appeared. The identity of these conjugates was established by microinjection experiments in which both proteins were labeled. At low doses of phenylhydrazine, the intracellular concentration of globin-ubiquitin conjugates was proportional to the rate of hemoglobin degradation. This result, together with the observation that ubiquitin conjugation to globin is markedly enhanced by phenylhydrazine-induced denaturation of hemoglobin, provides support for the hypothesis that the covalent attachment of ubiquitin to proteins signals proteolysis.

Effect of high mobility group nonhistone proteins HMG-20 (ubiquitin) and HMG-17 on histone deacetylase activity assayed in vitro

We have used a method previously described by Reeves and Candido (1) to partially release histone deacetylase from cell nuclei together with putative regulators of the enzyme. Histone deacetylase released from testis cell nuclei and its putative regulators were separated by gel filtration in Sepharose 6B. A peak of low molecular weight contains a heat-stable factor that stimulate histone deacetylase in vitro. Many of the properties of the activator coincide with those of the protein HMG-20 (ubiquitin). Ubiquitin isolated from testis cell nuclei stimulated histone deacetylase in vitro. It has been suggested that HMG-17 partially inhibits histone deacetylase in Fried cell nuclei (2). In our system, HMG-17 shows no inhibitory effect on histone deacetylase activity

Thymosins beta 8 and beta 9: two new peptides isolated from calf thymus homologous to thymosin beta 4

Two new peptides, designated thymosin beta 8 and thymosin beta 9, respectively, have been isolated and their amino acid sequences established. Thymosin beta 8, isolated from calf thymus fraction 5, has a mass of 4518 daltons and contains 39 amino acid residues, of which 31 are identical to the corresponding amino acid residues in thymosin beta 4 isolated from the same source. The NH2 terminus of thymosin beta 8 is acetylalanine, compared with acetylserine in thymosin beta 4. Thymosin beta 9, isolated from fresh-frozen calf thymus by a procedure that minimizes proteolysis, is identical to thymosin beta 8 except for the presence of an additional dipeptide, -Ala-LysOH, at the COOH terminus. It has a mass of 4717 daltons and 32 of its 41 amino acids are identical to those of thymosin beta 4. The similarity in structures of thymosin beta 4 and thymosin beta 9 suggests that they may have related functions.

Isopeptidase: a novel eukaryotic enzyme that cleaves isopeptide bonds

In an attempt to clarify the regulatory mechanism that accounts for the shift of protein A24 in the mitotic cycle, we demonstrated the existence of an enzyme, provisionally termed isopeptidase, that cleaves A24 stoichiometrically into histone H2A and ubiquitin. Properties of this enzyme are (i) most eukaryotes, including mammals, amphibia, chicken, and yeast, contain isopeptidase in the cytoplasm; (ii) a significant increase in enzyme binding to chromatin occurs when cells enter mitosis; (iii) Escherichia coli does not contain isopeptidase; (iv) isopeptidase has a molecular weight of 38,000; (v) at an ionic strength that induces globular conformation of H2A, isopeptidase activity is repressed; (vi) a SH group is an essential cofactor; and (vii) most divalent cations (except Mg2+ and Ca2+) are inhibitory. In view of the stoichiometric conversion of A24 into H2A and ubiquitin by isopeptidase in vitro, A24 probably contains a Gly-Gly dipeptide in isopeptide linkage but no other intervening polypeptides. Since ubiquitin in various eukaryotes binds to protein other than H2A, and is proteolytically released, isopeptidase probably acts on isopeptide bonds in general and not uniquely on those of A24. Inasmuch as isopeptidase is present throughout the cell cycle, the level of A24 in chromatin appears to be controlled by a balance between isopeptidase and an as yet unestablished H2A-ubiquitin ligase.

Modulation of T leukaemic cell phenotype with phorbol ester

A panel of monoclonal antibodies and other markers (e.g., terminal deoxynucleotidyl transferase, sheep erythrocyte rosettes, peanut agglutinin) have been used in conjunction with flow cytometry and biochemical analysis to monitor the induction of maturation in human thymic (T) leukaemic cell lines by phorbol ester (TPA). Seven cell lines underwent multiple phenotypic alterations in response to TPA but were unresponsive to synthetic thymic hormones (TP5, FTS) or to other compounds (e.g. DMSO, retinoic acid) which induce maturation in other types of leukaemia. The changes parallel those observed in normal T-cell differentiation and partly reflect alterations in glycosyl transferase activity, altered synthesis of proteins and regulation of cell surface receptors (for transferrin) associated with rapid growth and metabolism. These studies further illustrate the reversibility of maturation arrest in human leukaemia and provide support for the view that leukaemia may involve regulatory defects in the coupling of proliferation and maturation. Induction of promotion of terminal differentiation in leukaemic equivalents of T-cell precursors may provide a convenient system for the study of biochemical and molecular events involved in T-cell development and diversification.

Ubiquitin - protein conjugates

The data available at present indicates there are three distinct functions of ubiquitin, two of which are related to protein conjugation. The first of these has been extensively studied by our laboratory and others interested in nucleosomes and changes in chromatin states. The ubiquitin-histone (Ub-2A, Ub-2B) conjugation reaction now appears to be a very dynamic process. In the deconjugation (lyase) reaction, both the histone 2A and the ubiquitin are left intact and in a form which makes possible ready reconjugation. Accordingly, this may be a mechanism for "moment-to-moment" Control of the genome. The second function in which ubiquitin is conjugated involves proteolytic activity. This activity is correlated with protein turnover. In this process, the ubiquitin-protein conjugate apparently serves as a "signal" for the protease cleavage of the protein. The released ubiquitin is also intact and is probably available for reconjugation. In the third function, ubiquitin was suggested to serve as a "hormone". The studies thus far have been carried out primarily on induction of T- and B-lymphocytes, reduction or delay of Coombs' positivity and reduction of spleen weight. The precise physiological role of this reported function is still unclear, particularly because the ubiquitin used was probably not the physiologically active form.

Complete amino acid sequences of bovine thymopoietins I, II, and III: closely homologous polypeptides

Complete amino acid sequences were determined for thymopoietins I and II (revision), isolated from bovine thymus, and for thymopoietin III, a newly identified polypeptide isolated from bovine spleen. Thymopoietin III (TP-III) is a 49 amino acid monomeric peptide that shows minor microheterogeneity at residue 34. The three thymopoietins have largely identical sequences yet some distinct differences, suggesting very recent evolution from a common gene. The complete amino acid sequences are (Formula: see text).

Proton nuclear magnetic resonance study of an active pentapeptide fragment of ubiquitin

The aqueous solution conformation of Tyr-Asn-Ile-Gln-Lys (UB5) corresponding to positions 59-63 of the polypeptide, ubiquitin, has been investigated by proton NMR. Like the parent protein, UB5 induces nonspecifically both T and B lymphocyte differentiation. The various NH and CH resonances of this pentapeptide have been assigned, and its solution conformation has been probed through a study of chemical shift variations with pH, temperature dependence of amide hydrogen chemical shifts, vicinal NH--C alpha H and C alpha H--C beta H2 coupling constant data, and amide hydrogen-exchange rates. The latter were measured in H2O by using a combination of transfer of solvent saturation and saturation recovery NMR experiments. The data are compatible with the assumption of a highly motile dynamic equilibrium among different conformations for this peptide. The various secondary amide hydrogens remain essentially exposed to the solvent. The temperature-dependence study of the amide hydrogen chemical shifts also did not reveal any strong internal hydrogen bonds. A rotamer population analysis of tyrosine and asparagine side chains suggests that two of the rotomers are predominantly populated for each of these residues. From these results, a picture emerges of the dynamic conformation of UB5 in aqueous solution.

The ligand specificity of the (adenosine 3',5'-monophosphate)-binding site of yeast glyceraldehyde-3-phosphate dehydrogenase. Interaction with adenosine derivatives and pharmacologically-active compounds

The high-affinity cAMP-binding site of form-II yeast glyceraldehyde-3-phosphate dehydrogenase has a marked specificity for adenosine derivatives, such ligands including N6-substituted adenosine derivatives active as cytokinins n plant systems and adenine nucleotides. Of a wide range of nucleotides and nucleosides examined only adenosine derivatives bind to the cAMP binding site. A variety of antimitotic compounds (including colchicine, colcemid and phenylcarbamate derivatives), adrenergic receptor antagonists (alprenolol and propranolol) and non-steroidal anti-inflammatory agents (notably indomethacin and flufenamic acid) displace cAMP from glyceraldehyde-3-phosphate dehydrogenase. Colchicine, colcemid, N6-furfuryladenosine, indomethacin, flufenamic acid and propranolol inhibit cAMP binding to the enzyme in an apparently competitive fashion. Given the evolutionary conservatism and abundance of glyceraldehyde-3-phosphate dehydrogenase, the affinity of the cAMP-binding site of this enzyme for a variety of structurally-disparate pharmacologically-active compounds compromises simple one-site interpretations of physiological responses to these agents.

The release of high mobility group protein H6 and protamine gene sequences upon selective DNase I degradation of trout testis chromatin

Limited digestion of trout testis nuclei with DNase I selectively degrades the protamine genes. Concomitant with the degradation of transcribed DNA sequences a series of chromosomal proteins are released; among these, the major species corresponds to the high mobility group protein H6. The amounts of H6 released from chromatin by limited DNase I action and that in the residual nuclear pellet have been determined. A very high proportion of H6 is associated with DNase I sensitive chromatin regions.

High-resolution fractionation of nucleosomes: minor particles, "whiskers," and separation of mononucleosomes containing and lacking A24 semihistone

Staphyloccal nuclease digests of HeLa chromatin fractionated on low ionic strength nucleoprotein gels have been further analyzed by second-dimension DNA and protein gel electrophoresis. In vivo radioactive labeling of chromatin components and use of longer gels allowed a higher sensitivity and resolution than has been previously reported for this approach. A number of nonhistone protein spots and about 20 DNA spots can be detected in the mononucleosomal region of the second-dimension gel. In particular, there are three DNA spots identical in DNA size that correspond to three discrete kinds of core mononucleosomes resolved on the first-dimension nucleoprotein gel. Analysis of protein composition shows that the most rapidly migrating particle contains all four core histones but no A24 semihistone (A24 is a covalent conjugate of histone H2A and a specific nonhistone protein, ubiquitin), whereas the other two core mononucleosomes contain A24 semihistone. Thus, one can now quantitatively separate the A24-lacking core mononucleosomes from those containing A24, making it possible to directly address the question of whether A24 is associated with nucleosomes containing a specific subset of DNA sequences. Additional features of two-dimensional nucleoprotein-DNA patterns are "whiskers," which run slower than core mononucleosomes in the nucleoprotein dimension and both faster and slower than core-length DNA in the DNA dimension. In more extensive digests, "secondary whiskers" are observed, which run faster than core mononucleosomes in both dimensions and appear to coincide with previously described subnucleosomal particles SN7 and SN8 [Bakayev, V., Bakayeva, T. & Varshavsky, A. (1977) Cell 11, 619-629]. Possible mechanisms of whisker formation are discussed.

Current status of thymosin research: evidence for the existence of a family of thymic factors that control T-cell maturation

Thymosin fraction 5 contains several distinct hormonal-like factors which are effective in partially or fully inducing and maintaining immune function. Several of the peptide components of fraction 5 have been purified, sequenced and studied in assay systems designed to measure T-cell differentiation and function. These studied indicate that a number of the purified peptides act on different subpopulations of T-cells (see Figure 1). Thymosin beta 3 and beta 4 peptides act on terminal deoxynucleotidyl transferase (TdT) negative precursor T-cells to induce TdT positive cells. Thymosin alpha 1 induces the formation of functional helper cells and conversion of Lyt- cells to Lyt 1+, 2+, 3+ cells. Thymosin alpha 7 induces the formation of functional suppressor T-cells and also converts Lyt- cells to Lyt 1+, 2+, 3+ cells. These studies have provided further evidence that the thymus secretes a family of distinct peptides which act at various sites of the maturation sequence of T-cells to induce and maintain immune function. Phase I and Phase II clinical studied with thymosin in the treatment of primary immunodeficiency diseases, autoimmune diseases, and cancer point to a major role of the endocrine thymus in the maintenance of immune balance and in the treatment of diseases characterized by thymic malfunction. It is becoming increasingly clear that immunological maturation is a process involving a complex number of steps and that a single factor initiating a single cellular event might not be reflected in any meaningful immune reconstitution unless it is the only peptide lacking. Given the complexity of the maturation sequence of T-cells and the increasing numbers of T-cell subpopulations that are being identified, it would be surprising if a single thymic factor could control all of the steps and populations involved. Rather, it would appear that the control of T-cell maturation and function involves a complex number of thymic-specific factors and other molecules that rigidly control the intermediary steps in the differentiation process.

Evaluation of functional thymic hormones in Arabian horses with severe combined immunodeficiency

Arabian horses with severe combined immunodeficiency disease (SCID) were evaluated for thymic hormone activities using thymic extracts and sera. Extracts prepared from thymus of SCID horses were able to increase the number of spleen cells responding to sheep red blood cells in irradiated, bone marrow-reconstituted mice. In addition, ultrafiltrates prepared from sera of these immunodeficient horses, which contained material with molecular weight of less than 50,000 Daltons could (a) induce a population of human bone marrow precursor cells to differentiate into cells bearing SRBC receptors and form spontaneous E-rosettes, a characteristic of T lymphocytes, and (b) stimulate cyclic adenosine monophosphate (AMP) synthesis in mouse thymocytes. Based on in vivo and in vitro effects, it was concluded that the defect of these Arabian horses with severe combined immunodeficiency disease did not involve a complete thymic hormone inadequacy.

A synthetic pentapeptide with biological activity characteristic of the thymic hormone thymopoietin

The pentapeptide arginyl-lysyl-aspartyl-valyl-tyrosine, corresponding to amino acid residues 32--36 in thymopoietin, was synthesized. In vitro, this pentapeptide induced the differentiation of murine prothymocytes to thymocytes and inhibited differentiative induction of cells of the B lineage. This combination of actions is presently unique to the parent molecule thymopoietin. In vivo, the pentapeptide reduced the high numbers of autologous rosette-forming cells normally present in the spleens of athymic mice; this also is a property of thymopoietin. These results suggest that this readily synthesized pentapeptide corresponds to an active site of thymopoietin and might serve as a therapeutic substitute for thymopoietin.

Ultrastructural and histochemical features of the thymus glands of the adult lungless salamander, Plethodon glutinosus (Caudata: Plethodontidae)

The thymus glands of adult slimy salamanders (Plethodon glutinosus) were examined by light and electron microscopy with the objective of describing the populations of epithelial cells believed to be secretory. The results of various histochemical procedures designed to demonstrate nucleic acids, proteins, lipids, and mucosubstances were evaluated by light microscopy. Each thymus is incompletely subdivided into a variable number of interconnected lobules by trabeculae extending inward from a thin capsule composed of connective tissues. The thymic parenchyma lacks distinct cortical and medullary regions, although developing lymphocytes and plasma cells tend to accumulate in larger numbers in the outermost portions of the glands. Basophils are found regularly in the capsule and trabeculae, but only very rarely within the thymic parenchyma. The epithelial cells of the thymus can be classified into five categories: epithelial reticular cells; three varieties of granulated cells (types I, II, and III), and myoid cells. Epithelial reticular cells form a three-dimensional network which extends throughout all portions of the thymus. Type I and type II granulated cells can be distinguished from one another by various morphological criteria at the ultrastructural level, but only small differences in the composition of their inclusions can be demonstrated histochemically. Both types of granules are composed principally of a proteinaceous material containing an abundance of primary amino and guanidyl groups. In addition, most type I inclusions possess a lipid component that cannot be demonstrated in type II granules. Type III granulated cells possess very small cytoplasmic inclusions resembling those of gastroenteric endocrine cells. Myoid cells contain concentrically arranged myofibrils composed of sarcomeres. In favorably oriented material, small cysts can be identified whose walls are composed of mixtures of type I cells, type II cells, and epithelial reticular cells. Groups of degenerating epithelial cells form lamellated structures corresponding to Hassall's (thymic) corpuscles.

The isolation and partial characterization of low-molecular-weight phosphorylated component of the non-histone proteins of mouse nuclei

After labelling of mouse liver nuclei with [gamma-32P]ATP in vitro, 10-20% of the radioactivity incorporated into the saline-soluble nuclear and HAP2 chromatin fractions was located in a low-molecular-weight component (component 10) with pI near 4.5 in urea. By using combinations of ion-exchange chromatography, preparative thin-layer isoelectric focusing and gel filtration, this component was isolated from both nuclear fractions. Recovery from the saline-soluble fraction was poor under conditions that allow endogenous phosphatases to be active. Component 10 was shown to be a phosphoprotein on the basis of enzyme-digestion experiments and the detection of phosphoserine and phosphothreonine. The 32P radioactivity did not appear to be associated with phosphorylated basic amino acids. Its molecular weight was determined by gel chromatography and electrophoresis in sodium dodecyl sulphate/polyacrylamide gels as approx. 10000, and tryptic digestion of the reduced carboxymethylated protein in urea yielded two 32P-labelled peptides. It has not been possible as yet to assign a function to component 10, though its similarity to other low-molecular-weight acidic proteins is discussed.

Chemical synthesis of a hexadecapeptide segment of ubiquitin that activates adenylate cyclase and induces lymphocytes to differentiate

A hexadecapeptide corresponding to positions 59--74 of ubiquitin was synthesized and purified. The peptide was characterized by its mobility in TLC and electrophoresis, amino acid sequence and composition, and molar rotation. The peptide possessed approximately 40% activity compared with native ubiquitin in each of 3 biological assays in vitro: a) thymocyte induction, b) B cell induction and c) elevation of intracellular cyclic AMP levels in sarcoma 180 cells.

Presence of protein A24 in rat liver nucleosomes

Two-dimensional gel profiles of the 0.2 M H2SO4-soluble proteins of monomer nucleosomal fractions were found to contain protein A24. Protein A24 is of interest because it is composed of histone 2A and "ubiquitin", apparently joined by an isopeptide linkage [Goldknopf, I.L. & Busch, H. (1977) Proc. Natl. Acad. Sci. USA 74, 864-868; Hunt, L.T. & Dayhoff, M.O. (1977) Biochem. Biophys. Res. Commun. 74, 650-655]. Monomer nucleosomal fractions were obtained by sucrose density gradient centrifugation of micrococcal nuclease digests of rat liver nuclei. As shown by their DNA size, the monomer fractions were highly purified. Proteins A24 and Bu, another protein of unknown characteristics, were found along with histones 1, 2A, 2B, 3, and 4 in the monomer fractions in relative amounts similar to those found in extracts from whole nuclei and chromatin. Other acid-soluble proteins found in the nuclear and chromatin extracts were essentially absent from the monomer fraction. Inasmuch as protein A24 and Bu were found in lesser amounts than the histones, it is suggested that they are associated with specialized subsets of nucleosomes.

Circulating thymic-hormone activity in congenital immunodeficiency

Circulating thymic-hormone activity was assayed by measuring Thy 1-2 antigen induction on null lymphocytes from athymic mice incubated with human plasma or serum. Plasma from 19 normal children aged under 10 had inductive activity equivalent to 10-6-16-2 ng thymopoitin/ml. Plasma from 15 infants were severe combined immuno-deficiency, 2 of whom had appreciable immunoglobulin synthesis, and from 2 infants with DiGeorge syndrome had little or no inductive activity. Successful reconstitution with thymus or bone-marrow grafts and with red-cell infusions (if adenosine-deaminase deficiency is present) was followed by a rise in circulating thymic-hormone activity.

Rationale for combined use of fetal liver and thymus for immunological reconstitution in patients with variants of severe combined immunodeficiency

Bone marrow cells from a patient with severe combined immunodeficiency were studied in vitro for thymus-dependent lymphocyte (T cell) differentiation by using, at varying times, thymic epithelial monolayers and culture supernatants, thymopoietin, ubiquitin, and thymic extract as inducing agents. On initial evaluation, with thymopoietin or human thymic extract, only a partial differentiation of marrow cells was achieved into cells bearing the human T cell antigenicity without the capacity to form rosettes with sheep erythrocytes, suggesting that the stem cells were defective. Two fetal liver transplantations aimed at reconstitution were unsuccessful, despite evidence of chimerism. Induction studies at that time demonstrated rosetting capacity (with sheep erythrocytes) of the patient's bone marrow cells after coculture with thymic epithelial monolayers but not with their supernatants. An 18-week fetal thymus (irradiated) was then transplanted, but the transplantation was unsuccessful and no clear evidence of chimerism was demonstrated. Subsequently, transplantation of another fetal liver resulted in chimerism and immunologic reconstitution. Serum thymic factor activity rose from 1:2 before transplantation to 1:16 after reconstitution. The combined use of fetal thymus and liver may provide effective immunological reconstitution in some variants of severe combined immunodeficiency.

Bioassay determinations of thymopoietin and thymic hormone levels in human plasma

Thymopoietin is a thymic hormone that induces differentiation of thymocytes from precursor cells which arise in hemopoietic tissues. This paper describes a sensitive in vitro assay for the induction of Thy 1.2 antigen on null lymphocytes from germ-free athymic (nu/nu) mice. The sensitivity and specificity of the bioassay were increased by adding high concentrations of ubiquitin (a nonspecific inducer) to the induction incubations. The bioassay was sufficiently sensitive to detect thymopoietin at less than 0.25 ng/ml. A dose-response relationship was shown between thymopoietin concentration and the percentage of cells induced to express Thy 1.2 antigen. When normal human plasma was assayed, induction was registered with activity corresponding to thymopoietin at greater than 1 ng/ml in plasma from infants or young adults. Activities in the thymopoietin range of 0.25 ng/ml were registered with plasma from healthy subjects over 50 years of age. Thymectomy was followed by loss of this inductive activity from the plasma. This bioassay permits clinical studies on T (thymus-derived) cell inducers released by the human thymus into the circulation.

Thymic activity in severe combined immunodeficiency diseases

Thymic function was evaluated by quantitation of circulating thymic factor in patients with several forms of severe infantile immunodeficiency diseases. Direct quantitation of thymic factor in serum of patients with severe combined immunodeficiency revealed heterogeneity of this syndrome by this parameter, as was also shown by study of susceptibility of the marrow cells to differentiation in vitro. Thymic factor was not detectable in one patient with severe combined immunodeficiency, but was present in normal or near-normal concentrations in three others. Circulating levels of this hormonal activity were also not detectable in a patient with DiGeorge athymic syndrome. Following marrow or fetal liver transplantation, which corrected the severe combined immunodeficiency thymic factor levels either increased slightly or did not change appreciably. Fetal thymic transplantation, which together with fetal liver transplantation corrected the immunodeficiency in one patient with severe combined immunodeficiency, was associated with increase of thymic factor to normal levels. Fetal thymus transplantation alone, which was employed to correct the immunodeficiency of DiGeorge athymic syndrome, caused an increase in thymic factor activity to normal or near normal levels in this patient.

Prostaglandin E treatment of NZB/NZW mice

NZB/NZW F1 hybrid mice were treated with pharmacologic doses of prostaglandin E1 (PGE1) (200 microng subcutaneously either once or twice daily) from 6 through 52 weeks of age. PGE1-treated mice were protected against development anemia, clinical nephritis, and death. At 52 weeks 18 of 19 treated mice were alive, wherase only 2 of 19 untretreated control mice were alive. None of the 10 mice treated with PGE1 twice daily exhibited significant (greater than 2+) proteinuria at 1 year of age. PGE1 treatment did not prevent development of antibodies to nuclear antigens. The data also suggest that survival of NZB/NZW mice is prolonged when treatment with PGE1 is begun at 24 weeks, an age at which mice already show evidence of nephritis. Thus all 6 mice treated with PGE1 (200 microng sc twice daily) from 24 weeks were alive at 52 weeks, whereas only 2 of 6 untreated control mice were alive. The mechanisms whereby PGE1 treatment influences the course of disease in NZB/NZW mice are not known.

Thymus-like activities of sulphur derivatives on T-cell differentiation

Levamisole and sodium diethyldithiocarbamate can induce in vivo thymocyte differentiation from precursor spleen cells of nu/nu mice and evoke indirect plaque-forming cells in nude mice immunized with sheep red cells. These sulphur drugs induce in thymusless mice the production of a serum factor which transfer in vivo immune enhancement and in vitro thymocyte differentiation. In vivo treatment with sulphur derivative can substitute for an alleged thymice hormone.

Two main features of T-cell development: thymus traffic and postthymic maturation

It appears from the results presented in Table V and discussed in the preceding pages that a precursor population of immunologically competent T cells can be characterized and defined by multiple biological criteria as being probably of postthymic origin and substantially different from either the immunologically competent T lymphocyte or the prethymic stem cells. On the basis of recent data on functional characteristics of of different subsets of T cells, which suggest parallel lines of differentiation (see Chapter 2), it is possibile that the postthymic precursor compartment may also show heterogeneity; however, this cannot be presently asserted from our results.