Human prothymocytes. Membrane properties, differentiation patterns, glucocorticoid sensitivity, and ultrastructural features.

Abstract

Thymic precursor cells (prothymocytes) comprise a large proportion of the fetal thymic cell population, but are less frequently encountered in the postnatal thymus, where they compose < 1% of the entire population. In the present study we attempted to characterize a number of properties of the prothymocytes obtained from human fetal thymic tissues after depletion of the E-rosette thymocyes on a Ficoll-Hypaque gradient. The prothymocytes are larger than the thymocytes and show a different nuclear chromatin pattern. This subset of cells lacks the E-rosetting and natural-attachment capacities and, unlike thymocytes, does not bind the lectin peanut agglutinin. Human prothymocytes are highly sensitive to the in vitro cytolytic effect of hydrocortisone, whereas the thymocytes are resistant. Long-term in vitro culture of prothymocytes resulted in the expression of thymocyte characteristics together with a burst of mitotic activity. Results of this study indicate that the rate of the prothymocyte proliferation is regulated by the small thymocytes present in the same suspension.

Studies on Thymocyte Subpopulations in Guinea Pigs

“…In agreement with this, fetal human thymus contain a large proportion of RE-cells which are large, and hydrocortisone sensi tive [4], In rat thymus, on the other hand and in agree ment with our results, nonrosette forming cells but not rosette forming cells were found responsive to mi togens [36]. Since mitogen responsiveness is consid ered as an indication of maturity and since mature T lymphocytes are RE+, this is rather unexpected.…”

Human T Lymphocyte Antigens as Defined by Monoclonal Antibodies

“…It is beyond the scope of this paper to review all aspects of human thymocyte differentiation. These latter cells are regarded as thymic precursor cells and have been designated prothymocytes (Gatien et al 1975, Basch & Kadish 1977, Galili et al 1980. Studies in both rodents and humans have demonstrated that thymocytes originate from bone marrow precursor cells which migrate to the thymus (Moore & Owen 1967, Stutman 1977, Galili et al 1980.…”

“…What follows, therefore, is a summary of recent information derived from the use of anti-T cell specific monoclonal antibodies regarding differentiation pathways and tissue distribution of normal human T cells. Human thymic precursor cells are the predominant cell type in early fetal thymus and become rare in thymus obtained from individuals over age 2 (Gatien et al 1975). Ninety percent of thymocytes are found in the cortex, while the remaining 5-10% of thymocytes are in the thymic medulla.…”

Studies on Thymocyte Subpopulations in Guinea Pigs

“…We have recently found that population la (with the highest proportion of non-rosetting cells) contains proliferat ing cells, target cells for a thymocyte growth factor and mitogen-reactive cells and that these could be separated on the basis of differential binding of pea nut agglutinin (PNA), mitogen-reactive cells being PNA' [Sandberget al, 1983]. In man, both the inabili ty to form rosettes [Gatien et al, 1975] and the inabili ty to bind PN A [ Galili et al, 1980] were reported prop erties of immature prothymocytes. The possible rela tion between rosette formation and ability of thymo cyte populations la, lb and II of guinea pigs to bind PNA will be studied more in detail separately.…”