Search for Thymocyte Growth-Stimulating Activity in Extracts of Different Tissues and among Established Growth Factors and Thymic Maturation Hormones

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Purification of a thymocyte specific growth factor is described. A formic acid extract of calf thymus was acetone precipitated, extracted with acidic methanol and precipitated with ether. With an assay based on the stimulation of DNA synthesis in thymocyte cultures the crude extract was purified by several steps of gel filtration and ion exchange chromatography. The stimulating activity had an apparent M_r of 1,600 and a pI of 5.6–5.9 and was devoid of reactive amino groups. It behaved amphoteric and was sensitive to pronase. We propose that the activity resides in an N-terminal-blocked peptide without biochemical relationship to defined thymic differentiation hormones or established growth factors.

Section: Further Characterizationsupporting

confidence: 51%

New Preparative Schedule and Further Characterization of a Thymocyte Specific Growth Factor from Calf Thymus

Söder¹,

Ernström²

1983

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“…Interleukin-2 Assay IL-2 activity was determined by utilizing IL-2-dependent rat lymphoblasts obtained from primary cultures of concanavalin A (Con A) activated splenic lymphocytes, essentially as described previously [14,15]. An IL-2 standard, used as a positive control, was prepared from the conditioned medium of Con A-Sepharosestimulated spleen cells [ 14], Thymocyte Growth Peptide Assay TGP activity was evaluated by measuring the recruitment from G, into S phase of guinea pig thymocytes in short-term cultures [10].…”

Section: Lymphocyte Culturesmentioning

confidence: 99%

Isolation of Interleukin-1 from Human Milk

Söder

1987

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Human milk was investigated in regard to the presence of lymphocyte growth factors. Precipitated and dialyzed protein from mature human milk was found to exhibit interleukin-1 (IL-1) activity in the murine thymocyte proliferation assay. A mitogenic effect of milk protein was also observed in cultures of human and guinea pig thymocytes, demonstrating that the effect was not species restricted. No interleukin-2 or thymocyte growth peptide activity was found. Gel filtration chromatography on Sephadex G 150 revealed three distinct peaks of IL-1 activity, with apparent molecular weights of 14, 31 and 60 kilodaltons, respectively. Chromatofocusing showed IL-1 activity in four peaks, the major peak eluting at an isoelectric point of 5.0. Similar molecular heterogeneity has previously been demonstrated for IL-1 isolated from macrophages and other sources. The physiological role of milk-derived IL-1 is unknown, but it is proposed that it might act as an immunostimulating factor in the mammary gland, and hypothetically also in the breast-fed infant. Since IL-1 is a potent pyrogen, it is also suggested that milk-derived IL-1 contributes to the well-known pyrogenic activity of milk.

“…In previous papers, we have reported on the biochemical and functional properties of a thymic factor with ability to induce DNA synthesis specifically in immunologically in competent immature thymocytes [3][4][5]. The factor was shown to be biochemically and functionally distinct from other lymphocyte growth factors and from thymic differentiation hormones [6,7]. Kinetic studies showed that the thymic factor stimulated DNA syn thesis with a peak effect 4-8 h after start of culture [4,5], indicating that the target cells were Gl thymocytes which were influenced to initiate DNA synthesis.…”

Section: Introductionmentioning

confidence: 99%

Recruitment of Thymocytes from G1 into S Phase by a Thymic Factor

Söder¹,

Ernström²

1984

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A thymic factor previously shown to stimulate the DNA synthesis of immature thymocytes was found to recruit G1 cells synchronously into S phase within 1.5–2 h. The S + G2 + M duration of the cultured thymocytes was not affected. In the absence of the thymic factor, the responding thymocytes seemed to be blocked in G1 at a putative restriction point 1.5 h prior to S phase. When the addition of the thymic factor to cultured cells was delayed, the responsiveness rapidly declined, indicating that target cells were transferred into an unresponsive state. A stimulating effect of the DNA synthesis of cultured thymocytes was obtained also after a transient exposure to the thymic factor for 2–3 h. The stimulating activity was completely absorbed from the medium by incubation with thymocytes at both 4 and 37 °C, but not by lymph node lymphocytes which are unresponsive to the thymic factor. Our interpretation of the results is that the thymic factor acts on thymocytes in G1, triggering the responsive cells via membrane receptors to proceed from G1 into S phase. The thymic factor is proposed to be a progression factor for the rapidly cycling immature thymocytes and to be involved in the regulation of the intense thymic growth in vivo.