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PubMed2006

Thymus and myasthenia gravis: antigen processing in the human thymus and the consequences for the generation of autoreactive T cells.

Peptides displayed by antigen presenting cells in the thymus shape the T cell repertoire. We investigated the antigen processing machinery of the MHC class II presentation pathway and describe the differential expression of lysosomal proteases in compartments of the thymus and the peripheral lymphoid tissue. Overexpression of certain proteases found in the thymus and thymoma associated with myasthenia gravis is likely to affect tolerance induction and may promote the generation autoreactive CD4(+) T helper cells.

Antigen-Presenting Cells↗
PubMed1982

Elements of structure and ultrastructure of the blood-thymus barrier in ACTH involuted thymus.

The ACTH influence upon the thymus may be a reliable model for stress involution. In this case, the cortical lymphocytic depletion is accompanied by mast cell accumulation and increased caliber of the blood vessels. The blood-thymus barrier which has an active role in involution shows an enriched transport activity of the endothelial cells, great enlargement of the basement membrane, increased macrophage activity within the perivascular space with elevated values of acid phosphatase activity, and thickening of the fibrillar network. The epithelioreticular cells show plenty of vacuoles in their cytoplasm, the mitochondria undergo swelling processes, and their cristae are diminished. The ultrastructural data show that lymphocyte depletion is carried out by macrophage-mediated lymphocytolysis. But by counting the peripheral blood cells an earlier mechanism is revealed; i.e. migration through the enlarged but more permeable blood-thymus barrier. The epithelioreticular cells do not seem to have an active, direct implication in any of the phenomena.

Adrenocorticotropic Hormone↗
PubMed1982

Inhibitory effect of transplanted syngeneic thymus fragments, thymus epithelium and thymocytes on the increased contact sensitivity reaction in the adult thymectomized mouse.

Thymectomy in the adult mouse leads to an increased ability to develop contact sensitivity. The effect of different types of thymus grafts to adult thymectomized mice on contact sensitivity was studied in the present investigation. An inhibition was observed after transplantation either of uncultured thymus tissue, cultured thymus epithelium or of thymocytes. The results of the study favor the hypothesis that a continuous production of suppressor cells regulates contact sensitivity in the adult mouse.

Aging↗
PubMedDate not supplied

Maldescent of the thymus: 34 necropsy and 10 surgical cases, including 7 thymuses medial to the mandible.

Among 3236 pediatric necropsies over 23 years, abnormal position of thymic tissue was recorded in 34 cases. Cardiac anomalies, predominantly those seen in DiGeorge syndrome, were present in 24; 3 had noncardiac anomalies only, 4 had other diseases, and 3 were sudden infant deaths. Mediastinal thymic tissue was absent in 22 cases, small or unilateral in 7, and normal in 5. The maldescended thymic tissue was unilateral in 18, bilateral in 11, and multiple on one or both sides in 5. It was situated near the thyroid gland in 19, lower in the neck in 6, and higher in 9, including 7 medial to the submandibular salivary gland and 1 at the base of the skull. The maldescended tissue approached the size of a normal lobe of thymus in eight and was 2.4 to 0.1 cm in the remainder. Over the same period, in only two cases was no thymic tissue found. Among 68,000 surgical specimens over 40 years, there were 10 cases of ectopic thymus in the neck, including 1 cutaneous and 4 cystic. This frequency of thymic tissue in the neck may explain why lymphoid tissues are sometimes relatively normal in cases of absent mediastinal thymus and behooves a search in the submandibular salivary gland region and higher before diagnosing thymic agenesis.

Child↗
PubMed1979

Quantification of total IgM and IgG and specific IgM and IgG to a thymus-independent (LPS) and a thymus-dependent (tetanus toxoid) antigen in the rat by enzyme-linked immunosorbent assay (ELISA).

Rat IgM and IgG was determined by mechanized "sandwich" enzyme-linked immunosorbent assay (ELISA) using peroxidase labeled anti-rat-IgM and -IgG. Linear ranges in standard curves of a reference rat serum had a slope similar to the slopes found with sera of 25 rats of various age. IgM and IgG measurements by ELISA in these sera correlated well with results obtained by single radial immuno-diffusion (SRID). In addition, the precision of the enzyme immunoassay was the same as obtained with the SRID. Compared with SRID, ELISA is less time consuming and the amount of antiserum used in the macro-ELISA is one order of magnitude lower; and again 10 times lower in the mechanized micro-ELISA that is currently being developed. In conclusion, the ELISA is a specific, reliable, sensitive, and economic method for routine measurement of rat serum IgG and IgM e.g. in toxicity studies. In the second part of this study, ELISA and the passive hemagglutination test were compared to determine the primary and secondary antibody response to E. coli lipopolysaccharide (LPS) and tetanus toxoid in rats. In the ELISA, the antigens were bound to the wells of polystyrene microplates. Tetanus toxoid was coated directly, LPS after complexing with methylated bovine serum albumin. After incubation with dilutions of the rat sera, the amount of antibody bound to the solid phase was quantified by means of peroxidase-labeled antiimmunoglobulin. The specificity of the enzyme immunoassay was tested by absorption of the sera with the respective antigens. ELISA proved to be more sensitive than the hemagglution reaction, except when titers were determined during the secondary response to tetanus toxoid. Besides its specificity and sensitivity, ELISA is a convenient method for measuring both IgM and IgG antibodies. Finally, evidence is presented that in the rat, the humoral immune response to LPS is a thymus-independent phenomenon. Thus, by using the antibody response to LPS and tetanus toxoid in function studies of the immune system of the rat, insight can be obtained in the thymus-independent and thymus-dependent humoral immune response.

Age Factors↗
PubMed1982

Thymus cell migration: cells migrating from thymus to peripheral lymphoid organs have a "mature" phenotype.

To gain information on the lineage relationship of cells leaving the thymus, we studied the phenotype of thymus emigrants within hours of their exit. The migrants were identified in the peripheral lymphoid organs by their fluorescence, 3 to 4 hr after intrathymic injection of a solution of fluorescein isothiocyanate, a technique that initially only labels thymocytes. Migrants identified in this way were analyzed with rhodamine-anti-Thy-1 or rhodamine peanut agglutinin (PNA). They were found to express Thy-1 antigen and PNA binding sites at levels very similar to those found on the majority of peripheral T cells or medullary thymocytes and quite different from cortical thymocytes. Taken together with our previous experiments on Lyt-1, Lyt-2, and H-2 levels, the data show that cells leaving the thymus are quite mature in phenotype and are indistinguishable from peripheral T cells by all the criteria examined.

Animals↗
PubMed1980

Thymus-dependent and thymus-independent subpopulations of intestinal intraepithelial lymphocytes: a granular subpopulation of probable bone marrow origin and relationship to mucosal mast cells.

Intraepithelial lymphocytes have been examined histochemically in the small intestines of normal rats and mice and in thymus-deficient animals (B rats and nude mice). It is concluded that these cells are heterogeneous, consisting of at least two subpopulations. One population contains granules, is thymus-independent, and is probably bone-marrow-derived. The other population does not contain granules and appears to be thymus-dependent. It is suggested that the granular cell, which may be a precursor of mucosal mast cells, is more properly a previously unrecognized nonlymphoid leukocyte of bone marrow origin.

Animals↗
PubMed1975

Interactions between the immunological responses of a thymus-independent antigen (Salmonella adelaide O antigen) with a thymus-dependent antigen (sheep erythrocytes) in the adult bird.

The bird's antibody response to a thymus-dependent antigen (sheep erythrocytes) (SRBC) and a thymus-independent antigen (SALMONELLA ADELAIDE O antigen) were characterized: whereas the former proceeded through a brief 19S response to a declining 7S response, the latter failed to switch from 19S TO 7S for several weeks and consisted in repeated excursions of 19S antibodies. When injected intravenously and simultaneously an injection of S. adelaide-killed organisms and SRBC interact, so that the response to the latter fails to switch from 19S TO 7S and consists of repeated excursions of 19S antibodies. The changed character of the SRBC response is interpreted to be due to the relative lack of 7S antibody: passive 7S antibody to S. adelaide O antigen or 7S anti-SRBC produces a negative feedback inhibition of their respective responses, so that only one excursion of 19S antibody is observed. The effect is not, however, symmetrical; the thymus-independent antigen is dominant. Thus, whereas 7S antibody to S. adelaide produces the same negative feedback inhibition on the response to S. adelaide and the response to SRBC (when injected with adlaide), 7S antibody to SRBC inhibits only the response to SRBC and not the response to S. adelaide. These results are discussed relation to current hypotheses of antibody biosynthesis and mechanisms of adjuvant action. They are also discussed in relation to the function of the germinal centres of the spleen which may function to mediate the negative feedback of 7S antibody on the antibody response.

Adjuvants, Immunologic↗
PubMed1976

T- and B-areas in immune reactions. Volume changes in T and B cell compartments of the rat spleen following intravenous administration of a thymus-dependent (SRBC) and a thymus-independent (paratyphoid vaccin-endotoxin) antigen. A histometric study.

In the white pulp of rat spleens cell numbers were studied in the different compartments following intravenous administration of comparable doses of paratyphoid vaccine (PTV, thymus-independent) and sheep red blood cells (SRBC, thymus-dependent). In the periarteriolar lymphatic sheaths (PALS) both cell concentration and volume were measured. For the follicles and the marginal zone only volume was recorded in the first 5 days following antigen administration. Additionally, histologic observations were made. In the thymus-dependent area PTV caused oedema 12-24 hours after administration. Following SRBC administration an increase in lymphocyte numbers occurred until the second day, probably representing an influx of T cells from the recirculating pool. Both antigens gave rise to a plasmacellular reaction in the peripheral PALS (2nd-4th day). In the bone marrow-dependent areas a massive shift of medium-sized lymphocytes from the marginal zone to the follicles took place in the first 24 hours following PTV administration. These cells subsequently transformed into blasts. After SRBC (6 and 12 hours) only a few marginal zone lymphocytes seemed to migrate into the follicles. It is aruged that the endotoxin present in PTV is responsible for the fact that, following administration of the antigen, all marginal zone (B) cells responded. Endotoxin stimulation might provide a model for the fate of marginal zone cells stimulated by other agents, such as antigen (stimulating antigen binding B cells) or antigen-antibody complexes (stimulating Fc-receptor B cells).

Animals↗
PubMed1983

B cell activation. II. Receptor cross-linking by thymus-independent and thymus-dependent antigens induces a rapid decrease in the plasma membrane potential of antigen-binding B lymphocytes.

We report the specific induction of B cell plasma membrane depolarization with the use of thymus-dependent and -independent antigens. We have utilized various trinitrophenol-carrier conjugates for the stimulation of isolated trinitrophenol-binding mouse B cells. Membrane depolarization was assessed by flow cytometric analysis of 3-3'-pentyloxacarbocyanine iodide (DiOC5[3])-stained cells. Entry into the cell cycle was determined by flow cytometric analysis of acridine orange-stained cells. The results indicate that polyvalent antigens, but not free hapten, induce B cell membrane depolarization by a large proportion of antigen-binding cells within 2 hr of stimulation. Although all polyvalent antigens induce membrane depolarization, only thymus-independent antigens induce the subsequent G0 to G1 transition, suggesting that the membrane Ig cross-linking signal alone, although sufficient to induce membrane depolarization and subsequent increased IA expression, is insufficient to drive the entry of B cells into the cell cycle. The G0 to G1 transition appears to be dependent on a second signal, perhaps mediated by the thymus-independent carrier or antigen-specific, Ia-restricted T cell helper.

Animals↗
PubMed1993

IL-1 mRNA expression detected by in situ hybridization and polymerase chain reaction in human thymus and thymoma. Correlation with late T-cell maturation in normal versus neoplastic thymus.

Interleukin-1 has long been suggested to participate in the development of T-cells in the thymus. To determine whether IL-1 was produced in the human thymus, we used the technique of in situ hybridization and PCR amplification of mRNA. High levels of IL-1 mRNA were detected in cells at the cortico-medullary border, which separates immature from mature T-cells, suggesting a role for IL-1 in a late stage in T-cell maturation. IL-1 transcripts were detectable by a single step PCR reaction in these samples. We examined a series thymomas (human thymic epithelial tumors) that induce partial T-cell maturation: In this group of thymomas T-cells develop to the cortical stage but not beyond. We failed to detect high levels of IL-1 mRNA expression in these tumors by in-situ hybridization, IL-1 mRNA was detected only in one of these samples by a single step PCR amplification. However, all of the samples were positive, when analyzed with a more sensitive, two step amplification of IL-1 mRNA by the use of nested primers. These results are consistent with the hypothesis that higher level of IL-1 expression is either the consequence of, or required for late T-cell maturation.

Adult↗
PubMed1982

Patterns of isotype expression by B cell clones responding to thymus-dependent and thymus-independent antigens in vitro.

It was found that the Type 2 thymus-independent (TI-2) antigens bacterial levan, trinitrophenyl-Ficoll, and pneumococcal carbohydrate vaccine (PnC) stimulate clonal expansion and antibody secretion in splenic fragments from either hemocyaninprimed or unprimed irradiated recipients bearing B cells from unprimed donors. The in vitro stimulation with TI-2 antigens leads to the expression of isotype switching and provides a more balanced variety of isotypes than is usually observed in vivo. Still, some characteristic patterns of isotypes expressed in vivo to either TI-2 or thymus-dependent (TD) antigens are preserved in vitro. Frequencies of phosphocholine (PC)-reactive B cells responding to either PnC or to PC-hemocyanin (PC-Hy) suggest an appreciable overlap in populations responding to these TI and TD forms of antigen. The existence of a population responsive to either form of PC determinant is supported by the observation that many clones arising in the presence of both forms of antigen express patterns of isotypes that appear as summations of those distinct patterns shown by clones responding to only one form or the other. These data suggest that PC-Hy- and PnC-responding cells may derive from a linear rather than a branched pathway of B cell development and that expression of isotype switching over the lifetime of a developing B cell clone may be regulated in a manner dependent on the form of the stimulating antigen.

Animals↗
PubMed1997

Phenotypic and immunohistological analyses of the human adult thymus: evidence for an active thymus during adult life.

We analyzed cellular content of thymic samples from 26 human healthy donors, ranging from 1 week postnatal to 49 years old. Our results showed that there was an overall decrease in cellular density, beginning early during life, but with two peaks of cellular density, at 9 months and 10 years of age. Histological and immunohistological analyses showed that variations in cellular density were correlated with the morphological changes observed during thymic involution, namely the enlargement of interlobular trabeculae and the development of adipocytic tissue. However, the adult thymus still contained thymocytes, up to 49 years. Phenotypic analysis showed no significant variations according to the age of donors in the distribution of the main thymocyte subsets, both precursors and more mature cells. These results suggest that the human thymus remains active during adult life.

Adolescent↗
PubMed1987

Basement membrane proteins and reticulin in a normal thymus and the thymus in myasthenia gravis.

The distribution of basement membrane (BM) proteins, laminin and type IV collagen were studied immunohistochemically in a series of 12 normal thymuses representing different age groups (0-52 years) and in 10 cases of myasthenia gravis (age 7-53 years). The staining pattern was compared with that of conventional reticulin staining. BM proteins were present at the capsule-parenchyma interface and scantily distributed in the medullary stroma, where they were closely associated with reticulin fibres. The extrathymic perivascular space was effectively visualized by the staining of the BM's marginal to it. The fiber network present in this space stained with reticulin stain and, less continuously, in BM stainings. Lymph node like tissue with germinal centers was occasionally present in the perivascular spaces in normal thymuses and commonly in the myasthenia gravis cases, where the perivascular spaces were often dilated. The BM's of the perivascular space were mostly continuous in normal cases, but discontinuities were observed in cases of myasthenia gravis, especially in the spaces which were widely dilated. Immunohistochemical detection of BM proteins seems to be useful in the study of thymic structure, particularly in the demonstration of the characteristic changes of the perivascular space in myasthenia gravis. It is suggested that the reticulin fibres present in the medulla and in the perivascular space contain laminin and type IV collagen.

Adolescent↗
PubMed1982

Formation of 6-dimethylcarbamyloxy-dGuo, 6-dimethylamino-dGuo and 4-dimethylamino-dThd following in vitro reaction of dimethylcarbamyl chloride with calf thymus DNA and 6-diethylcarbamyloxy-dGuo following in vitro reaction of diethylcarbamyl chloride with calf thymus DNA.

The rodent carcinogens dimethylcarbamyl chloride (DMCC) and diethylcarbamyl chloride (DECC) react with dGuo (pH 7.0-7.5, 37 degrees C, 4 h) to form the O6-acyl derivatives 6-dimethylcarbamyloxy-2'-deoxyguanosine (6-DMC-dGuo) and 6-diethylcarbamyloxy-2'-deoxyguanosine (6-DEC-dGuo), respectively. Reaction of DMCC with dThd under identical conditions yielded 4-dimethylamino-thymidine (4-DMA-dThd). Compounds 6-DMC-dGuo and 6-DEC-dGuo undergo a nucleophilic aromatic substitution reaction with dimethylamine (DMA) to form 6-dimethylamino-2'-deoxyguanosine (6-DMA-dGuo) via displacement of the C-6 dialkylcarbamyloxy moiety. The substitution reaction did not take place when diethylamine or NH3 were substituted for DMA. The structures of the new compounds 6-DMC-dGuo, 6-DEC-dGuo, 4-DMA-dThd and 6-DMA-dGuo were deduced from chemical analyses and syntheses, UV and nuclear magnetic resonance (NMR) spectra and electron impact, isobutane chemical ionization and source insertion isobutane chemical ionization mass spectra. It was postulated that 4-DMA-dThd was formed following reaction of the transient intermediate 4-DMC-dThd with DMA formed by hydrolysis of DMCC. Calf thymus DNA was reacted in vitro with DMCC (pH 7.0-7.5, 37 degrees C, 4 h) and the modified DNA hydrolyzed enzymatically to 2'-deoxynucleosides. Compounds 6-DMC-dGuo, 4-DMA-dThd and 6-DMA-dGuo were identified in the hydrolysate by high-pressure liquid chromatography (HPLC). In an identical manner 6-DEC-dGuo was identified following in vitro reaction of DECC with calf thymus DNA. Compounds 6-DEC-dGuo and 6-DMC-dGuo possess novel structures with respect to the types of adducts known to be formed between carcinogens and bases in DNA. The implications of these findings with respect to chemical mutagenesis and carcinogenesis is discussed. The structural relationship between N4-dimethyl-5-methylcytosine (4-dimethylamino-Thy) formed in DNA following in vitro reaction with DMCC and 5-methylcytosine, the only modified base found in vertebrate DNA is noted.

Animals↗
PubMed1991

Effects of polychlorinated biphenyls with Ah receptor affinity on lymphoid development in the thymus and the bursa of Fabricius of chick embryos in ovo and in mouse thymus anlagen in vitro.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and its congeners bind to the Ah receptor and are known to cause thymic atrophy in most experimental animal species and also to inhibit lymphoid development in the embryonic thymus (T-cells) and in the bursa of Fabricius of chick embryos (B-cells). The coplanar polychlorinated biphenyls (PCBs) 3,3',4,4'-tetrachlorobiphenyl (TCB), 3,3',4,4',5-pentachlorobiphenyl (PeCB), and 3,3',4,4',5,5'-hexachlorobiphenyl (HCB) (relatively strong Ah receptor ligands) and the mono-ortho-chlorinated analogues of TCB and PeCB (relatively weak Ah receptor ligands) were administered to chick embryos by air chamber injection on Day 13 of incubation. The numbers of lymphoid cells (on Day 19) in the thymus and the bursa of Fabricius were lower, in a dose-dependent manner, in embryos treated with the coplanar PCBs compared with controls. Approximate ED50 values for inhibition of bursal cell development were 4 micrograms for PeCB, 50 micrograms for TCB, and 300 micrograms/kg egg for HCB. The most immunotoxic of the mono-ortho-chlorinated analogues of TCB and PeCB were about 1000 times less potent than PeCB. The in vitro effects of the PCBs were studied in organ cultures of thymi from 15-day-old mouse fetuses. The three coplanar chlorobiphenyls inhibited lymphoid development in this culture system in a dose-dependent manner. PeCB was only about 10 times less potent (EC50 approximately 2 x 10(-9) M) than than TCDD (EC50 approximately 2 x 10(-10) M), whereas HCB and TCB were about 100 times less toxic than PeCB. No inhibition of lymphoid development by the mono-ortho-chlorinated PCBs was observed using concentrations as high as 10(-6) M.

Animals↗
PubMed1977

RNA synthesized in vitro by calf thymus RNA polymerase III (C), as well as by E. coli RNA polymerase, is restricted to a subset of calf thymus DNA.

RNA synthesized in vitro from chromatin and DNA by calf thymus RNA polymerase III was evaluated by hybridization in vast DNA excess. The RNA contains RNA complementary to both moderately repeated and unique DNA sequences. Very highly repeated DNA is not transcribed. A greater portion of RNA transcribed from DNA by RNA polymerase III hybridizes to moderately repeated DNA than RNA transcribed by Escherichia coli RNA polymerase. In studies utilizing DNA absorbed to filters, RNA transcribed from chromatin in short incubations hybridized to a greater extent than RNA transcribed for longer times. Similar results were obtained with RNA transcribed from DNA by E. coli RNA polymerase. These results suggest: 1) RNA polymerase III may be responsible for the synthesis of RNA species in addition to tRNA and 5 S ribosomal RNA and a portion of this RNA is transcribed from unique DNA; and 2) in vitro there may be selectivity in the initiation of transcription by both E. coli RNA polymerase and calf thymus RNA polymerase III.

Animals↗
PubMed1983

T-cell maturation in the human thymus and tonsil: peanut agglutinin binding T lymphocytes in thymus and tonsil differ in maturation stage.

The finding of peanut agglutinin (PNA) binding capacity, supposed to be a marker of immature lymphocytes, within the T-cell population of the human thymus (58%) and tonsil (10%) prompted the comparison of maturation stages of PNA binding (PNA+) and nonbinding (PNA-) T cells in both organs. The proliferative response after mitogenic stimulation of purified PNA+ fractions was significantly less than that of purified PNA- fractions. The results of mitogen dose-response experiments, of variation in time of culture harvest, and of addition of irradiated allogeneic peripheral blood non-T cells indicated the intrinsic mitogen unresponsiveness of cells in the PNA+ fractions. The mitogen response of tonsil fractions was higher than that of thymocyte fractions. Cells with an immature immunologic phenotype were enriched in the thymocyte PNA+ fraction, and almost absent in the tonsil fractions. Both tonsil fractions contained cells with the immunologic phenotype of mature T cells, and showed a purine interconversion enzyme makeup comparable to mature T lymphocytes. It is concluded that the tonsil PNA+ T cell is a functionally immature lymphocyte which is in a further maturation stage than PNA+ or PNA- thymocytes. The presence of PNA+ T cells outside the thymus is of relevance for the clinical evaluation of PNA binding assays and suggests the occurrence of T-cell maturation within the tonsil environment.

Cell Separation↗