Isolation of a polypeptide that has lymphocyte-differentiating properties and is probably represented universally in living cells

Heterogeneity of stem cells in severe combined immunodeficiency

Two patients with severe combined immunodeficiency disease (SCID) having variable B-cell development have been shown to have marrow precursors of lymphoid cells which can be induced in vitro by thymic factors to express certain T-cell surface characteristics (HTLA+ phenotypes). Their marrow cells could not, however, be induced by these same factors to develop the E-rosette marker or functional activities of T lymphocytes. The marrow of these children also showed, when compared to that of normal adults, a different distribution of cellular elements on density gradient fractionation. The findings support the view that the disorder under study has a different pathogenesis from other forms of SCID previously analysed.

Aplastic anemia: presence in human bone marrow of cells that suppress myelopoiesis

Bone marrow from a patient with aplastic anemia was shown by multiple criteria to have a block in early myeloid differentiation. This block was overcome in vitro by elimination of marrow lymphocytes. Furthermore, this differentiation block was transferred in vitro to normal marrow by coculturing with the patient's marrow. We suggest that some cases of aplastic anemia may be due to an immunologically based suppression of marrow cell differentiation rather than to a defect in stem cells or their necessary inductive environment.

Terminal deoxynucleotidyl transferase is found in prothymocytes

Terminal deoxynucleotidyl transferase is an enzyme which has the unique property of polymerizing polydeoxynucleotides onto a primer in the absence of a template (1,2). This enzyme is found both in the thymus and the bone marrow of birds, rodents, and humans (3-7). Whether the marrow cells that contain terminal transferase are related to thymocytes, or are on a separate pathway of differentiation, is not yet known (7,8). To determine the lineage of the murine bone marrow cells that have terminal transferase, we have investigated whether these cells have the antigen Thy-1 induced on the cells by treatment with thymopoietin (9). Thymopoietin is known to induce a set of characteristic T-cell markers including the Thy-1 alloantigen on the surface of a subpopulation of bone marrow cells committed to T-cell differentiation (prothymocytes) (10). Destruction of Thy- 1-positive cells after exposure to thymopoietin allows elimination of a substantial fraction of those bone marrow cells that can repopulate an irradiated thymus (11). We find that such an elimination after induction with the thymic polypeptide removes a substantial amount of terminal transferase from the bone marrow cell population, suggesting that at least one-half of the marrow cells bearing this enzyme are related to those found in the thymus.

Lymphocyte-differentiating hormone of bursa of fabricius

Induction of early lymphocyte differentiation was studied in vitro in fractionated bone marrow cells of newly hatched chickens, with alloantiserums to identify newly differentiated B cells (Bu-1+) and T cells (Th-1+). Thymus extract induced selective T cell differentiation; the activity of the extract corresponds to that of thymopoietin. Bursal extract induced both B cell and T cell differentiation, but at lower concentrations B cell differentiation was always greater. This activity is ascribed to a lymphocyte-differentiating hormone of the bursa of Fabricius, for which the name bursopoietin is suggested.

An altered apurinic DNA endonuclease activity in group A and group D xeroderma pigmentosum fibroblasts

Endonuclease activity upon depurinated DNA was measured in extracts of cultured fibroblasts from xeroderma pigmentosum patients. Cell lines from complementation groups A, B, C, E, and the XP-variant had slightly reduced levels of activity, but cell lines from complementation group D had one-sixth of the normal activity. An altered pH dependence and a higher apparent Km for substrate in D-cell lines indicate that the remaining activity is also qualitatively different from the activity found in normal cells. A higher Km was also found in cell lines from the A-complementation group but not in cell lines from the C-complementation group. These defects in apurinic DNase might account for the neurological disorders in patients from the D- and the A-complementation groups.

Immature T lineage lymphocytes in athymic mice. Presence of TL, lifespan and homeostatic regulation

Lymphocytes belonging to the T lineage were described in athymic nude mice. We showed previously that they were distinguished from usual peripheral lymphocytes by their low density of theta antigen, their slow electrophoretic mobility and their absence of recirculation through the thoracic duct. We now report that they also express the TL antigen, have a life span of 1 to 2 days, are produced in the bone marrow and are under the homeostatic influence of the thymus. Indeed they appear rapidly in surgically T-deprived mice and their production is blocked in both surgically or congenitally athymic mice receiving a thymus graft. This homeostatic control may be mediated via a humoral factor. Cells with similar characteristics are present in the thymus at early stages of embryogenesis. The characteristics of these T lineage lymphocytes strongly suggest that they may represent "pre-thymocytes", i.e. cells already committed to the T pathway independently of thymic influence but needing the thymus microenvironment to differentiate further.