Antigen-specific T-cell memory is preserved in children treated for acute lymphoblastic leukemia

Despite profound T-cell immunodeficiency, most patients treated with chemotherapy do not succumb to infection. The basis for residual protective immunity in lymphopenic patients is not known. We prospectively measured T-cell numbers, thymopoiesis, and T-cell memory in 73 children undergoing a 2-year chemotherapy regimen for acute lymphoblastic leukemia (ALL) and compared them to an age-matched cohort of 805 healthy children. Most patients had profound defects in CD4 and CD8 T-cell numbers at diagnosis that did not recover during the 2 years of therapy. Thymic output and the fraction of naive T cells were significantly lower than in healthy controls. However, the remaining T-cell compartment was enriched for antigen-experienced, memory T cells defined both by phenotype and by function. This relative sparing of T-cell memory may, in part, account for the maintenance of protective immunity in lymphopenic patients treated for ALL. Moreover, because the memory T-cell compartment is least affected by ALL and its treatment, strategies to induce immunity to pathogens or tumor antigens in cancer patients may be most successful if they seek to expand pre-existing memory T cells.

Changes in thymopoiesis in myasthenia gravis

This study was undertaken to investigate T-cell maturation in hyperplastic thymi of patients suffering from myasthenia gravis (MG). For this purpose, the expression of the major differentiational molecules (CD4, CD8, and CD3/TCRalphabeta) and that of the regulatory and activation molecules on thymocytes from MG patients and control subjects were estimated by flow cytometric analysis. In the MG patients the increase in relative proportion of immature (CD4-8- TCRalphabeta-) and the most mature (CD4+8- TCRalphabetahigh and CD4-8- TCRhigh encompassing immunoregulatory NKT) thymocytes followed by a decrease in that of CD4+8+CD3-/TCRalphabeta- cells was found. Furthermore, in these patients the relative proportion of CD4+HLA-DR+ and CD4+71+ cells was increased, whereas that of CD4+25+ cells was slightly, but significantly, decreased (reflecting, most likely, decreased contribution of T reg cells bearing this phenotype). Moreover, in MG thymi the percentage of CD45RA+ cells was reduced indicating changes in the selection processes. In keeping with this finding the reduced thymocyte apoptotic index and percentage of cells bearing apoptosing (CD4-8- TCRalphabetalow) phenotype were detected. In conclusion, the study demonstrates substantial changes in intrathymic differentiation of T cells in hyperplastic MG thymi and suggests alterations in selection events providing an increased escape of potentially autoreactive T-cell clones, on one side, and an altered maturation and/or selection of immunoregulatory cells (NKT and CD4+8-25+ T reg cells) keeping these cell clones under control, on the other side.

TP-3 immunotoxins improve antitumor activity in mice with osteosarcoma

We measured the antitumor activity of two types of TP-3 immunotoxins that target an antigen expressed in tumors associated with osteosarcoma. Development of novel agents for treatment of patients with osteosarcoma is important. We previously described a monovalent-disulfide-stabilized recombinant immunotoxin made from the TP-3 antibody. This agent is called TP-3(dsFv)-PE38 and is cytotoxic to human osteosarcoma cells in vitro. To improve antigen binding, we designed and produced a bivalent immunotoxin, TP-3(dsFv)2-PE38. We evaluated the activity of both molecules in vitro and in vivo using tumor-bearing mice. Compared with the monovalent TP-3 immunotoxin, the bivalent TP-3 immunotoxin showed an approximately sevenfold increase in cytotoxic activity against three osteosarcoma cell lines which react with the TP-3 monoclonal antibody. The apparent affinity of the bivalent TP-3 immunotoxin was 12-fold greater than that of the monovalent TP-3 immunotoxin. The antitumor activities of both TP-3 immunotoxins were measured using severe combined immunodeficient mice bearing osteosarcoma cell line OHS-M1 tumors. The dose at which the bivalent TP-3 immunotoxin produces complete regressions of tumors is (1/2) that of the monovalent TP-3 immunotoxin. Increasing the avidity of TP-3(dsFv)-PE38 significantly improves its cytotoxic activity in vitro and results in a twofold increase in antitumor activity in vivo. Because TP-3-based immunotoxins have good antitumor activity in mice, these molecules merit additional development for possible treatment of osteosarcoma in humans.

Comparative study of antioxidant properties of immunoregulatory peptides

We studied antioxidant properties of immunofan, bursin, cyclobursin, thymopoietin II fragment, glycine, and Siberian ginseng. Experiments were performed in 2 model systems: Fe(2+)-induced oxidation of multilamellar phospholipid liposomes in a heterogeneous water-lipid system and oxidation of luminol induced by alpha,alpha'-azo-bis(isobutyramidine dihydrochloride) in a homogenous aqueous system. By the ability to entrap lipid peroxyl radicals, antioxidant activity of substances decreased in the following order: Siberian ginseng extract>bursin>cyclobursin>thymopoietin II fragment>immunofan, glycine. Siberian ginseng extract and thymopoietin II fragment interacted with Fe(2+), which contributed to elimination of catalyst of lipid peroxidation from the system. The ability of substances to interact with aqueous peroxyl radicals and luminol radicals decreased in the following order: Siberian ginseng extract>thymopoietin II fragment>immunofan>glycine, cyclobursin, bursin. Substances with high antioxidant activity improved the state of the endogenous antioxidant system and protected cells from oxidative stress. They entrapped reactive oxygen species formed in the cytoplasm, modulated free radical processes, and regulated the synthesis of bioactive molecules.

Nuclear envelope organization in papillary thyroid carcinoma

Papillary thyroid carcinomas (PTCs) have characteristic nuclear shape changes compared to follicular-type thyroid epithelium. We tested the hypothesis that the altered nuclear shape results from altered distribution or expression of the major structural proteins of the nuclear envelope. Lamin A, lamin B1, lamin C, lamin B receptor (LBR), lamina-associated polypeptide 2 (LAP2), emerin, and nuclear pores were examined. PTC's with typical nuclear features by H&E were compared to non-neoplastic thyroid and follicular neoplasms using confocal microscopy, and semi-quantitative immunoblotting. Lamin A/C, lamin B1, LAP2, emerin, and nuclear pores all extend throughout the grooves and intranuclear inclusions of PTC. Their distribution and fluorescent intensity is not predictably altered relative to nuclear envelope irregularities. By immunoblotting, the abundance (per cell) and electrophoretic mobilities of lamin A, lamin B1, lamin C, emerin, and LAP2 proteins do not distinguish PTC, normal thyroid, or follicular neoplasms. These results do not support previously published predictions that lamin A/C expression is related to a loss of proliferative activity. At least three LAP2 isoforms are identified in normal and neoplastic thyroid. LBR is sparse or undetectable in all the thyroid samples. The results suggest that the irregular nuclear shape of PTC is not determined by these nuclear envelope structural proteins per se. We review the structure of the nuclear envelope, the major factors that determine nuclear shape, and the possible functional consequences of its alteration in PTC.

Emerin expression at the early stages of myogenic differentiation

Emerin is an ubiquitous protein localized at the nuclear membrane of most cell types including muscle cells. The protein is absent in most patients affected by the X-linked form of Emery-Dreifuss muscular dystrophy, a disease characterized by slowly progressive muscle wasting and weakness, early contractures of the elbows, Achilles tendons, and post-cervical muscles, and cardiomyopathy. Besides the nuclear localization, emerin cytoplasmic distribution has been suggested in several cell types. We studied the expression and the subcellular distribution of emerin in mouse cultured C2C12 myoblasts and in primary cultures of human myoblasts induced to differentiate or spontaneously differentiating in the culture medium. In differentiating myoblasts transiently transfected with a cDNA encoding the complete emerin sequence, the protein localized at the nuclear rim of all transfected cells and also in the cytoplasm of some myoblasts and myotubes. Cytoplasmic emerin was also observed in detergent-treated myotubes, as determined by electron microscopy observation. Both immunofluorescence and biochemical analysis showed, that upon differentiation of C2C12 cells, emerin expression was decreased in the resting myoblasts but the protein was highly represented in the developing myotubes at the early stage of cell fusion. Labeling with specific markers of myogenesis such as troponin-T and myogenin permitted the correlation of increased emerin expression with the onset of muscle differentiation. These data suggest a role for emerin during proliferation of activated satellite cells and at the early stages of differentiation.

Detection of DNA fragmentation of myonuclei in myotonic dystrophy by double staining with anti-emerin antibody and by nick end-labeling

To clarify the occurrence of apoptosis in skeletal muscle in pathological conditions, we studied 44 muscle biopsy specimens by immunohistochemical staining with monoclonal antibody against emerin, which is localized in muscle nuclear membrane, and by ApopTag Plus to detect DNA fragmentation. Five of six patients with myotonic dystrophy (DM) showed three to 35 myonuclei stained with anti-emerin antibody and ApopTag Plus in 1500 muscle fibers. Four of the 18 patients with polymyositis, one of those with thyroid myopathy and one with neurogenic atrophy showed a few myonuclei stained positively by these methods. Our study revealed that DNA fragmentation in myonuclei occurred in skeletal muscle fibers regardless of the type of disease, although the frequency was rather low in all of these diseases except DM. The DNA fragmentation detected in most of the patients with DM suggested a significant role of apoptosis in the pathomechanism of this disease.

On the role of thymopoietins in cell proliferation. Immunochemical evidence for new members of the human thymopoietin family

Thymopoietins (TMPOs) are a group of ubiquitously expressed nuclear proteins. They are suggested to play an important role in nuclear envelope organization and cell cycle control, as has been shown for lamina-associated polypeptides 2 alpha and beta, which are the rat homologs of human TMPOalpha and TMPObeta, respectively. The recent isolation and characterization of seven mouse TMPO mRNA transcripts named TMPO-alpha, beta, beta', gamma, epsilon delta and zeta, suggest that more than the three previously reported transcripts, alpha, beta, and gamma forms, may exist in humans. Here we report on the demonstration of putative human TMPOdelta and epsilon by immunoblotting of human cell lines using a newly prepared polyclonal antiserum against the common N-terminal region of TMPO. Furthermore, we prepared the first truly TMPO-beta-specific, affinity-purified polyclonal antiserum, using a part of the human analog of the beta-specific domain of mouse TMPO 220-259 for immunization. We showed that human TMPObeta is highly expressed in all cancerous cells tested, while hardly any cross-reactivities with other proteins could be detected. In contrast to the high expression of human TMPObeta in the cancer-derived neuroblastoma cell lines SK-N-MC and SMS-KAN, we found very low expression of human TMPObeta in low-proliferative nerve tissue. These data led us to the assumption that expression of TMPObeta may correlate with the occurrence of cancer, and therefore may serve as a new tumor marker, or even as a new target for cancer therapy.

Distribution of emerin and lamins in the heart and implications for Emery-Dreifuss muscular dystrophy

Emerin is a nuclear membrane protein which is missing or defective in Emery-Dreifuss muscular dystrophy (EDMD). It is one member of a family of lamina-associated proteins which includes LAP1, LAP2 and lamin B receptor (LBR). A panel of 16 monoclonal antibodies (mAbs) has been mapped to six specific sites throughout the emerin molecule using phage-displayed peptide libraries and has been used to localize emerin in human and rabbit heart. Several mAbs against different emerin epitopes did not recognize intercalated discs in the heart, though they recognized cardiomyocyte nuclei strongly, both at the rim and in intranuclear spots or channels. A polyclonal rabbit antiserum against emerin did recognize both nuclear membrane and intercalated discs but, after affinity purification against a pure-emerin band on a western blot, it stained only the nuclear membrane. These results would not be expected if immunostaining at intercalated discs were due to a product of the emerin gene and, therefore, cast some doubt upon the hypothesis that cardiac defects in EDMD are caused by absence of emerin from intercalated discs. Although emerin was abundant in the membranes of cardiomyocyte nuclei, it was absent from many non-myocyte cells in the heart. This distribution of emerin was similar to that of lamin A, a candidate gene for an autosomal form of EDMD. In contrast, lamin B1 was absent from cardiomyocyte nuclei, showing that lamin B1 is not essential for localization of emerin to the nuclear lamina. Lamin B1 is also almost completely absent from skeletal muscle nuclei. In EDMD, the additional absence of lamin B1 from heart and skeletal muscle nuclei which already lack emerin may offer an alternative explanation of why these tissues are particularly affected.

Aberrant intracellular targeting and cell cycle-dependent phosphorylation of emerin contribute to the Emery-Dreifuss muscular dystrophy phenotype

The product of the X-linked Emery-Dreifuss muscular dystrophy gene is a protein called emerin, which is localized to the nuclear membrane. We have expressed full-length recombinant human emerin in an in vitro coupled reticulocyte system; it has a molecular mass of 34 kDa, inserts into microsomes in a type II orientation, and does not exhibit any N-linked glycosylation or cleavage event. Affinity-purified human emerin antiserum cross-reacts with the in vitro-expressed emerin and with a 34 kDa band present in a wide range of human tissue samples. Expression and subcellular distribution of emerin were studied in lymphoblastoid cell lines established from four patients with Emery-Dreifuss muscular dystrophy containing different mutations in the emerin gene. Emerin protein was detected in two of these patients by immunoblotting. In striking contrast to wild-type emerin, which was localized to the nuclear fraction and was insoluble in non-ionic detergents and high salt, emerin from these two patients exhibited a more random subcellular localization and increased solubility. On the basis of the mutations present in these patients, it would appear that emerin possesses two non-overlapping nuclear envelope targeting sequences. We have also demonstrated that emerin can occur in four different phosphorylated forms, three of which appear to be associated with the cell cycle. The mutant forms of emerin taken from the two patients exhibited aberrant cell cycle-dependent phosphorylated forms. This data suggests that for emerin to function normally it must be correctly localized, retained at the nuclear membrane and phosphorylated by cell cycle-mediated events.

Thymopentin and splenopentin as immunomodulators. Current status

Splenopentin (SP-5, Arg-Lys-Glu-Val-Tyr) and thymopentin (TP-5, Arg-Lys-Asp-Val-Tyr) are synthetic immunomodulating peptides corresponding to the region 32-34 of a splenic product called splenin (SP) and the thymic hormone thymopoietin (TP), respectively. TP was originally isolated as a 5-kDa (49-amino acids) protein from bovine thymus while studying effects of the thymic extracts on neuromuscular transmission and was subsequently observed to affect T cell differentiation and function. TP I and II are two closely related polypeptides isolated from bovine thymus. A radioimmunoassay for TP revealed a crossreaction with a product found in spleen and lymph node. This product, named splenin, differs from TP only in position 34, aspartic acid for bovine TP and glutamic acid for bovine splenin and it was called TP III as well. Synthetic pentapeptides (TP-5) and (SP-5), reproduce the biological activities of TP and SP, respectively. It is now evident that various forms of TPs were created by proteolytic cleavage of larger proteins during isolation. cDNA clones have been isolated for three alternatively spliced mRNAs that encodes three distinct human T cell TPs. The immunomodulatory properties of TP, SP, TP-5, SP-5 and some of their synthetic analogs reported in the literature have been briefly reviewed.

Peptides related to FKBP 39-45 loop possess immunostimulative potency

Taking into account the sequential homology existing between thymopoietin II, the DNA-binding domain of p53 protein and FKBP (FK-506 binding protein), a series of fragments of human and bovine FKBP containing a fragment Ser39-Pro45 were synthesized. In the humoral in vitro test all the peptides act as stimulators. Whereas in the in vivo test peptides derived from bovine FKBP show an immunostimulative and those from human FKBP an immunosuppressive activity. However, after blocking the Asp residue by a Bzl group the peptide V appears to be an immunostimulator. The data obtained suggest that these peptides can influence the immune system by blocking the FKBP receptor.

Domain-specific disassembly and reassembly of nuclear membranes during mitosis

The nuclear envelope contains three distinct membrane domains, the outer membrane, the inner membrane, and the pore membrane, that reversibly vesiculate in mitosis. We previously suggested from single-labeling immunofluorescence microscopy analysis of mitotic cells in culture that mitotic vesiculation of the nuclear membranes may proceed in a domain-specific manner (Chaudhary and Courvalin, J. Cell. Biol. 122, 295-306, 1993). In the present study, we add biochemical support to this hypothesis by sorting domain-specific mitotic vesicles. Antibodies directed against the lamin B receptor, a marker of the inner membrane, and glycoprotein gp210, a marker of the pore membrane, were used to isolate by affinity two populations of mitotic vesicles that were selectively enriched in each of these markers. These two vesicle populations were of different size distribution; the pore membrane-derived vesicles were smaller (80% being < or = 200 nm) than the inner membrane-derived vesicles (80% > or = 200 nm). Double-labeling immunofluorescence microscopy analysis of mitotic cells in culture showed that the time course and topology of disassembly and reassembly of inner and pore membrane domains were different, confirming that domain-specific vesicles are generated during mitosis. In these studies, protein LAP2/thymopoietin beta, another marker of the inner nuclear membrane, was segregating as lamin B receptor, suggesting that both proteins were contained in the same mitotic vesicles.

Expression of thymopoietin beta/lamina-associated polypeptide 2 (TP beta/LAP2) and its family proteins as revealed by specific antibody induced against recombinant human thymopoietin

An expression vector was constructed to produce a common region of human thymopoietin family proteins. The recombinant protein was expressed in Escherichia coli as a fusion protein with a biotinylated tag region and purified by affinity chromatography on a monomeric avidin resin. The thymopoietin family-specific antibody was induced in rabbits by immunization with the recombinant fusion protein. Western blotting analysis using the antibody revealed that the expression of thymopoietin family proteins was remarkably tissue specific. Among those, thymopoietin beta/lamina-associated polypeptide 2 appears to be specifically expressed in tissues with high proliferative activity.

Experiments on an early protection against foot-and-mouth disease virus

The influence of the peptide diacetylsplenopentin (SP5) on an early protection of guinea pigs against foot-and-mouth disease (FMD) was investigated. 80% protection was achieved if SP5 was applied in a dose of 2 mg one day before challenge with FMD virus (FMDV) type O1 Lausanne strain. In comparison with this a conventional commercial adsorbate vaccine protected guinea pigs about 7 days after vaccination. An earlier protection can be obtained in general by vaccination with a higher content of the immunogen. A tenfold increase of the 146 S particle dose in a conventional oil adjuvanted FMDV vaccine protected pigs about 2 days earlier as observed after inoculating a "normal" vaccine (about 11 days).

Use of monoclonal antibodies to identify thymopoietin in cultured human thymic epithelial cells

Murine monoclonal antibodies (mAbs) were developed to discriminate thymopoietin, a human thymic hormone, and thysplenin, a closely related molecule found in spleen. Three of these recognized both native and synthetic thymopoietin as well as thysplenin. Together they define two non-overlapping epitopes which withstand sodium dodecyl sulfate denaturation and can be detected by western blotting. We used these three mAbs to demonstrate the production of thymopoietin by cultured thymic epithelial cells for up to several weeks. Three additional mAbs were selective for thysplenin. Highly specific mAbs will be useful for characterizing further these physiologically distinct polypeptides.

Synthesis of [Glu34]human splenin (hSP) and examination of its immunological effect on the reduced B-lymphocytes of uremic patients

[Glu34]human splenin (hSP) was synthesized in a conventional manner by assembling ten peptide fragments followed by deprotection with 1 M trifluoromethanesulfonic acid-thioanisole (molar ratio, 1:1) in trifluoroacetic acid in the presence of m-cresol and dimethylselenide. Finally, the deprotected peptide was incubated with dithiothreitol to reduce sulfoxide on the methionine side chain. Incubation of peripheral lymphocytes isolated from uremic patients with the synthetic [Glu34]hSP showed an enhancing effect on the reduced B-lymphocytes, but synthetic human thymopoietin (hTP) had no effect under the same conditions.

Myasthenic sera recognize the human acetylcholine receptor bound to thymopoietin

The thymic hormone, thymopoietin (Tpo), from human (HTpo), bovine (BTpo) and from synthetic (sHTpo) origins bound to the acetylcholine receptor (AChR) solubilized by Triton 1.5% from human muscle. This binding was demonstrated either by inhibition of formation of radiolabeled alpha bungarotoxin (alpha Bgt)-AChR complexes measured after precipitation by ammonium sulfate or by a myasthenic serum containing a high concentration of anti-AChR antibodies, or directly by incubating the human AChR with radiolabeled sHTpo or BTpo. The 125I-labeled alpha Bgt-AChR complexes were totally inhibited by 10(-6) M sHTpo or BTpo. The complexes formed by AChR and the radiolabeled Tpo were recognized specifically by sera containing anti-AChR antibodies from myasthenic patients. The active pentapeptide derivative of Tpo, thymopentin, another thymic hormone, thymulin, as well as bovine insulin did not interfere with the specific binding of alpha Bgt to human AChR. Tpo and anti-AChR antibodies could participate together in the inhibition of neuromuscular conduction with Tpo modulating the depressive effect of the antibodies on the neuromuscular junction in myasthenia gravis.

[Structural similarity and functional activity of molecular fragments of staphylococcal enterotoxin B and thymopoietin II]

Structural similarity between Staphylococcus enterotoxin B and a thymus hormone, thymopoietin, has been revealed concerning thymopentin, one of active centres of thymopoietin. Fragments of enterotoxin B homologous to thymopoietin and their analogues were synthesized their immunological activity studied. Acetyl derivative of the fragment 225-229 of enterotoxin B increased infectional resistance and stimulated delayed type of hypersensitivity reaction.

Immunoregulating peptides II. In vitro effects of TP5 analogs on E-rosette formation and cell division

The effects of seventeen synthetic analogs of thymopentin (TP-5) have been studied in the active and azathioprine-inhibited E-rosette tests. Thymopentin was gradually shortened from the C terminus to peptides and single amino acids. Thymopoietin 32-34 (Arg-Lys-Asp-RGH-0205-TP-3) (II) and thymopoietin 32-35 (Arg-Lys-Asp-Val-RGH-0206-TP-4) (I) were the most active peptides. Dipeptide Arg-Lys produced significant stimulatory effect on azathioprine (ED75) inhibited E-receptor. Treatment of azathioprine (ED75)-inhibited E-rosette forming cells (ERFC) with arginine or especially lysine increased the number of ERFC. Some of TP-4 analogs decreased further the number of ERFC decreased by azathioprine ED30. These "suppressive" peptides as well as TP-3 caused a partial arrest of K 562 cell proliferation up to 96 hours. Results suggest that TP-5 is not the smallest active fragment of thymopoietins, since peptides (TP-3 and TP-4) exhibit similar or higher T-cell membrane activation on E-receptor. Arginine, lysine, and acidic aspartyl residue seem to be a necessary basic structure to produce a cumulative chemical signal on the activity of T-lymphocytes.

Antibodies to thymopoietin following implantation of paper disks derivatized with synthetic Cys-thymopoietin

A synthetic peptide corresponding to Cys-thymopoietin 28-39 was synthesized and coupled by diazo linkages to aminophenyl thioether-derivatized paper disks. Disks were implanted in the peritoneal cavities of mice, initially after soaking in complete Freund's adjuvant and subsequently, at 3 week intervals, without further treatment. After four implantations, 6/6 mice developed antibodies reacting with the synthetic peptide and with native thymopoietin. In contrast, mice conventionally immunized with peptide alone (six mice) or with peptide complexed with thyroglobulin (six mice) all failed to develop antibodies. Mice immunized with disks derivatized with Cys-thymopoietin 9-20, corresponding to the other hydrophilic region of thymopoietin, also failed to develop antibodies. Thymopoietin 28-39 corresponds to an antigenic hydrophilic region of thymopoietin that contains the pentapeptide active site (thymopoietin 32-36, Arg-Lys-Asp-Val-Tyr).

Immunohistochemical localization of thymopoietin with an antiserum to synthetic Cys-thymopoietin28-39

Thymopoietin-containing cells in the thymus were identified immunohistochemically using murine antiserum generated by immunization with synthetic Cys-thymopoietin28-39 (Cys-TP28-39). human thymopoietin, This antiserum, previously shown to react with both bovine and human thymopoietin, gave reactivity restricted to cortical and medullary epithelial cells of bovine and human thymus. Monoclonal antibodies with reactivity restricted to native bovine thymopoietin did not react with tissue sections of bovine thymus; most likely the epitopes recognized by monoclonal antibodies are not expressed on the inactive precursor forms of thymopoietin within thymic epithelial cells.

[Immunologically active peptides stimulating the T-cell system]

The known immunologically active peptides are compared from the standpoint of their chemical structure. Homologous potentially active fragments are determined. The revealed regularities in formation of peptides and active sites of proteins permit supposing that the process of peptide biogenesis from precursors involve the quasicyclization simultaneously with the limited proteolysis.

Immunoassay for bovine serum thymopoietin: discrimination from splenin by monoclonal antibodies

A polyclonal rabbit anti-bovine thymopoietin antiserum was used to develop a radioimmunoassay and sandwich enzyme-linked immunosorbent (ELISA) assay for the thymic hormone thymopoietin. Both assays showed slightly less sensitivity for the closely related splenic hormone splenin (SP) than thymopoietin (TP) and markedly less sensitivity for the human as compared with the bovine polypeptides. A number of murine monoclonal antibodies specific for bovine thymopoietin were generated; they were unreactive with bovine splenin and were also unreactive with human thymopoietin and splenin. A sandwich ELISA using these monoclonal anti-TP antibodies together with polyclonal rabbit anti-TP was specific for bovine thymopoietin and measured 300-500 ng/ml thymopoietin in bovine serum. Similar approaches are being pursued to develop an immunoassay for thymopoietin in human serum.

Thymopoietin in rheumatoid arthritis

In a controlled study involving 36 patients, thymopoietin was shown to be more effective than levamisole and as effective as penicillamine in improving the clinical status of patients with rheumatoid arthritis. There were small reductions in erythrocyte sedimentation rate and IgG which did not achieve statistical significance. Rheumatoid factor titre did not change. Although its mechanism of action is almost certainly related to its immunomodulatory properties it does not seem to be the same as that of levamisole.

Evolutionary relationship of thymopoietin to immunoglobulins and cellular recognition molecules

The sequence of thymopoietin, a thymic hormone composed of 49 amino acids, was compared to sequences of immunoglobulins and related cellular recognition molecules. Maximum homology was found between an active site of thymopoietin and homologous regions of IgG, IgE, beta 2-microglobulin, HLA-B7 and the Thy-1 antigen predicted to mediate immunologic activities, including Fc receptor binding. These results suggest that thymopoietin may be derived from approximately one half of the ancestral domain common to immunoglobulins and related immune system molecules and provide further support for a general theory that predicts the location of active sites in molecules of the immune system.

Thymic hormones and immunopeptides

The role of the thymus and its hormones in immunity is discussed. The known characteristics of various thymic factors, their mode of action and possible clinical applications are also reviewed. A brief discussion of other immunopeptides which are liberated by lymphocytes is also included.