Thymus tissue

Cytosine and thymine were first isolated by hydrolysis of calf thymus tissue by Albrecht Kossel (1853-1927) and A. Neumann during 1893-1894. Thymine s structure was published in 1900 and confirmed over the next several years when it was synthesized by several investigators. In 1903, cytosine was synthesized by Henry Lord Wheeler (1867-1914) and Treat B. Johnson, confirming its structure. Uracil was first isolated in 1900 from yeast nucleic acid found in bovine thymus and herring sperm. The methylation of uracil produces thymine thymine is also called 5-methyluracil because methylation takes place at the fifth carbon in uracil to produce thymine. 

Same of the common names of these bases reflect the circumstances of their discovery. Guanine, for example, was first isolated from guano (bird manure), and thymine was first isolated from thymus tissue. 

Gorman AM, Hirt UA, Zhivotovsky B, Orrenius S, Ceccatelli S. Application of a fluoro-metric assay to detect caspase activity in thymus tissue undergoing apoptosis in vivo. J Immunol Methods 1999 226 43-48. 

The mechanism by which zinc mediates Immune function is not clear the depression of DNA synthesis during zinc deficiency is implicated (9. McCaffrey et al. (97) demonstrated that a zinc-containing DNA polymerase is present in the thymus but does not appear in the mature T cell. A reduction in thymus tissue caused by zinc deficiency would adversely affect the immunocompetence of thymocytes. This hypothesis has been confirmed in experiments where a sharp drop in the thymic hormone is induced by zinc deficiency. 

Thymocytes from AKR/j and C3H mice (Jackson Laboratory, Bar terbor, >fe.) were obtained by gently teasing apart thymus tissue in PBS. The cells were washed in buffer and lightly-fixed in 0.125 6 glutaraldehyde-PBS for 20 minutes. Thymocytes from each strain were incubated with C3H anti OAKR antiserum, washed in buffer, and then treated with goat anti-mouse Ig antibody-latex conjugates. 

The isolation of thymic humoral factor (THF) by Trainin and colleagues was the culmination of studies to explain their observation that thymus tissue... 

Thymostimulin (TS) is an extract of calf thymus glands that has been partially purified by Falchetti et al. (1977) in Italy. Calf thymus tissue is first minced and extracted with ammonium acetate. This extract is then fractionated with ammonium sulfate precipitation. The 0-25% ammonium sulfate cut is further purified by ultrafiltration on an Amicon PM-10 membrane, desalted on Sephadex G-25, and gel filtered on Sephadex G-50. The biologically active preparation exhibits two predominant bands on polyacrylamide gels at pH 8.6. At the present time there have been no attempts to further define the constituents of this partially purified preparation. Although TS is similar to thymosin fraction 5 in its purification schema, a 0-25% ammonium sulfate precipitation step is used, whereas a 25-50% saturation fractionation cut is employed for the isolation of thymosin fraction 5. In addition, the purification procedure for TF5 includes an acetone precipitation step, whereas this procedure is not included in the preparation of TS. Thus, there... 

Oj. A second possibility is that a virus could invade thymic epithelial cells and viral modified epithelium would be subject to an autoimmune attack resulting in cell death and release of thymosin oij. In this regard it has been demonstrated that histological sections of thymus tissue in autopsy specimens from patients dying of AIDS exhibited changes characteristic of autoimmune destruction (Seemayer et al., 1984 Davis, 1984). Alternatively, the virus itself could cause thymic epithelial cells or nonthymic cells to increase production of a variety of proteins, some of which could cross-react in the thymosin assay. Finally, the increased serum thymosin Oj reactivity could reflect cross-reactivity to the viral agent of AIDS. 

In contrast to DiGeorge s syndrome, thymus transplantation has usually not been successful in patients with SCID (van Bekkum, 1973 Hong, 1976), although occasional T cell reconstitution has been noted (Murphy et al., 1976). In a more rational approach, thymus tissue has been transplanted in conjunction with fetal liver as a source of stem cells for treatment of SCID,... 

The concept that thymic hormones exist is now well accepted. However, many controversies still persist because of the multiplicity of different thymic products that have been isolated from thymus tissue over the past several decades. Many of the peptides appear to fulfill at least some of the accepted criteria for categorization as true thymic hormones. However, it is still unclear whether the various thymic polypeptides are components of a single thymic hormone (prohormone) that is capable of exhibiting the complete gamut of biologic properties ascribed to all of the different thymic peptides or whether each peptide alone or in certain combinations with other factors, at both intrathymic and extrathymic locations, regulates specific steps of T cell maturation. In this section we will review the biologic properties attributable to thymic factors in both animals and man. 

Thymosin ai, Talpha 1, Ac-SDAAVDTS SE ITTKDLKEKK EWEEAEQ, a linear, N-terminaUy acetylated 28-peptide hormone, secreted by thymus tissue (— thymosins) and primarily involved in stimulation of the thymus-dependent immune system. Synthetic thymosin ai (Zadaxin ) is used for the treatment of HBV and hepatitis, and in combination with low doses of interferon or interleukin (IL-2) it has found application in the treatment of cancer [J. F. Bach,/. Immunophar-macol. 1979, 1, 277 A. BUlich, Curr. Opin. 

Terminal deoxynucleotidyl transferase (TdT), an enzyme found in bone marrow and thymus tissue, can extend a DNA primer by 5 —> 3 polymerization using deoxyri-bonucleoside triphosphates as substrates. The primer must be at least three nucleotides... 

CT-polymerase B (DNA-dependent RNA-polymerase) was obtained from calf-thymus tissues and assayed as reported earlier (71). Activity measurements were performed in a toluen1e system, using a Liquid Scintillation Counter Mark I (Nuclear Chicago). 

Fig. 4A,B Acid-urea PAGE of P]-poly(ADP-ribosyl)ated histone HI isolated from histone Hl-DNA complexes. Histone Hl-DNA complexes (H1/DNA 1/1) were produced according to Hsiang and Cole [21] and were poly(ADP-ribosyl)ated by the purified calf thymus poly(ADP-ribose) polymerase (2 jug/OD unit) at 200 ijlM NAD and precipitated by 20% TCA (CI3 AcOH). Histone HI was extracted as described by Aubin et al. [8, 9] and was subjected to electrophoresis on 2.5 M urea - 0.9 N acetic acid vertical slab gels according to Panyim and Chalkley [17]. a 30 s pulse, b-d 5 min, 15 min, 30 min 200 tiMf NAD chase at 30°C, respectively. A Stained gel, B autoradiogram of the gel. The arrow indicates hyper(ADP-ribosyl)ated forms of histone HI. Histone HI and DNA have been isolated from calf thymus tissue...

Pick (1926) has called the consistent limitation of abnormal findings to spleen, liver, lymph nodes and bone marrow the most striking morphologic feature of GD. In the meantime exceptions to this rule, particularly in infants, have been described. Almost complete replacement of the thymus tissue by GC with concomitant GC deposition in the lymphatic tissue of the bowel was seen by Rusca (1921). Since, however, deposition of lipids in reticulum cells of the thymus may also be observed in infants with nutritional problems or infections (Lubarsch 1918), these cells may be mistaken for GC. Enlargement of the thymus in GD may occur without formation of GC. 

OsoBA, D., and Miller, J. F. A. P. (1964). The lymphoid tissue and immune responses of neonatally thymectomized mice bearing thymus tissue in Millipore diffusion chambers. J. Exptl. Med. 119, 177-194. 

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