Radioresistant cells of thymus--producers and targets of thymocyte growth factor and their possible role in postradiation restoration of thymus.

In the present study the association between the damaging and the stimulating action of radiation on the cells of thymus (in particular intrathymic T-lymphocyte precursors, TLP) is analyzed. The radioresistance and possibility to secrete humoral products, in particular, the thymocytes growth factor, THGF, is assessed. The possible role of THGF in the postradiation restoration of thymus is also discussed.

[Characteristics of the mitogenic activity of purified thymocyte growth factor]. / Kharakteristika mitogennoi aktivnosti ochishchennogo faktora rosta timotsitov.

Being purified by gel filtration and reverse phase HPLC the thymocyte growth factor from the supernatant of the cell line of intrathymic precursors of T-lymphocytes can stimulate the growth of splenocytes and thymocytes nonactivated by mitogen. Addition of suboptimal doses of mitogen or phorbol myristate acetate does not enhance the cell response to the thymocyte growth factor. The thymocyte growth factor in capable of stimulating the growth of thymocytes synergistically with interleukin-2, but the direct action of the thymocyte growth factor is not mediated by the production and reception of interleukin-2 and interleukin-4.

Purification and characterization of a thymocyte growth factor. 1. Purification.

A thymocyte growth factor has been purified by gel filtration and reverse-phase hplc from the culture medium of a T-lymphocyte-precursor cell line TC.SC-1/2.0. The purified thymocyte growth factor possesses high growth-stimulating activity and has a relative molecular mass of 20,000, as determined by SDS-PAGE.

Purification and characterization of a thymocyte growth factor. 2. Biological activity of the thymocyte growth factor.

A thymocyte growth factor, THGF, purified from the supernatant of a thymic T-lymphocyte-precursor cell line (TC.SC-1/2.0), stimulated the growth of splenocytes and thymocytes that had not been activated by a mitogen. Addition of suboptimal doses of mitogen or phorbol myristate acetate did not enhance the response. The growth factor could stimulate the growth of thymocytes synergistically with interleukin 2 but its action was not mediated by interleukin 2 or by interleukin 4. L3T4-Lyt2- thymocytes, Ig- splenocytes, Ig+ splenocytes, and alpha 1-thymosin-sensitive splenocytes were targets for THGF, which also stimulated the formation of haemopoietic spleen colonies in irradiated mice.

Properties of intrathymic T-lymphocyte precursors--targets of thymocyte growth factor (THGF).

Primary and long-term thymocyte cultures were used to analyze intrathymic T-lymphocyte precursors (TLP), the targets of thymocyte growth factor (THGF). It is shown that THGF has an effect on TLP not only as a growth factor, but also, and first of all, as an activation factor, triggering autocrine TLP proliferation. This is realized through secondary products, such as IL-2, IL-3, and THGF of endogenous origin, secreted by the THGF target cells. The intrathymic TLP that respond to THGF are resistant to high doses of irradiation (up to 50 Gy), and because they are in a quiescent state they can remain viable for long periods under unfavourable culture conditions. These TLP are apparently the self-renewing stem cells of the thymus, and are probably involved in the regeneration of this organ under extreme and adverse conditions, providing TLP of other types with growth factors. Data are presented which suggest that proliferation of the THGF target cells is realized in an unusual way, combining formation of daughter cells within the mother cell with ordinary mitosis.

Bone marrow and intrathymic precursors of T-cells produce a factor which enhances colony formation in the spleen.

Bone marrow Ig-Thy-1-SC-1- stem cells (precursors of T-lymphocytes, PTL, containing the SC-1 antigen) spontaneously secrete a humoral factor. When bone marrow Ig-Thy-1-SC-1- cells were treated with this factor they became able to form haemopoietic colonies in the spleens of lethally irradiated mice. This new colony-stimulating factor (CSF) is thermostable and has a molecular mass of about 25-30 kDa. Production of the CSF by bone marrow SC-1+Thy-1- cells was stimulated by treatment with the thymus preparation Thymoptin. Such treatment of bone marrow SC-1+Thy-1- cells also induced the production of a suppressor factor (thermolabile, molecular mass about 45 kDa), that reversed the effect of the CSF. The CSF and the suppressor factor are both also produced by cortisone-resistant radioresistant L3T4-Lyt-2-SC-1+ thymocytes (i.e. intrathymic PTL). The regulation of haemopoiesis appears to be a normal function of bone marrow PTL.

[Radiation stimulation of the production of thymocyte growth factor and its possible role in thymus recovery]. / Stimuliatsiia oblucheniem vyrabotki faktora rosta timotsitov i ego vozmozhnaia rol' v vosstanovlenii timusa.

Cells of two lines originating from intrathymic precursors of mouse T-lymphocytes produce an autocrine growth factor. The factor production during a certain period of the development of lines is drastically increased by radiation. The stimulatory effect of radiation cannot be explained by the release of the factor due to cell death. The administration of cultural supernatants, containing thymocyte growth factor, to the exposed mice favours the recovery of the thymus at early times following irradiation and influences the thymocyte response to the effect of growth factors.

[T-lymphocyte precursors--the target cells of thymocyte growth factor]. / Predshestvenniki T-limfotsitov--kletki-misheni faktora rosta timotsitov.

The cortisol-resistant PNA+SC- --1+Thy--1+-thymocytes are the target cells for the thymocyte growth factor (THGF), which is produced by the lines of transformed precursors of T-lymphocytes (PTL). These cells have the same properties and markers as the intrathymic PTL. The bone marrow cells do not proliferate in response to THGF but acquire that ability after the influence of thymic hormones, which induce the maturation of PTL. Thus, THGF is the autocrine growth factor of intrathymic PTL.

[Lines of transformed mouse thymus cells. II. Cell morphology, karyology, ultrastructure and growth in vitro and in vivo]. / Linii transformirovannykh kletok timusa myshi. II. Morfologiia, kariologiia, ul'trastruktura, rost kletok in vitro i in vivo.

Morphology, fine structure, karyology and growth of intrathymus pre-T-cell cultures (TC.SC-1/1.1 and TC.SC-1/2.0) were studied both in vitro and in vivo. The cultures were induced by injecting to mice a supernatant enriched with interleukin 2. The results obtained confirm the malignant transformation of cells of the lines obtained and the involvement of endogenic lymphotropic viruses in this process. The lines obtained are defective in hypoxanthine phosphoribosyltransferase. This property may serve as a basis for their use in hybridoma technology.

[Lines of transformed murine thymus cells. I. Production of the lines]. / Linii transformirovannykh kletok timusa myshi. I. Poluchenie linii.

Supernatant of activated cells of human T-leucosis line "Jurkat" enriched with interleukin-2 (IL-2) was injected to Balb/c mice. After a number of injections the animals were sacrificed and the thymus cells were cultured in vitro. Transformed cell clones were formed on days 3-4. Two stable T-cell strains of the reproduced primary cells were obtained (TC.SC-1/1.1. and TC.SC-1/2.0). The strains corresponded to the transitional stage of pre-T-lymphocytes and consisted of tumour cells. A possible mechanism of malignant transformation of these cells is discussed.