Restoration of the T lymphoid system of nude mice: different regeneration of neonatal and adult thymuses.

When a neonatal thymus and an adult (reticuloepithelial) thymus from normal mice are simultaneously grafted to individual adult nude mice, the host-derived T cell precursors regenerate the neonatal thymus more efficiently than the adult (reticuloepithelial) thymus. Thus, this is a direct cause for the poor restoration of the T lymphoid system of nude mice by adult and/or reticuloepithelial thymus grafts.

T lineage lymphocytes in nude mice born from homozygous nu/nu parents.

T lineage cells are found in the spleen of neonatal nu/nu mice born from nu/nu x nu/nu matings, and also in old, healthy nude mice obtained from the usual nu/+ x nu/nu matings. Their presence in neonatal nude mice which were never in contact with mother or normal littermate thymus products shows that commitment of stem cells towards the T lineage does not require the influence of the thymus.

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.

Development of surface immunoglobulins in the chicken.

B-cell maturation in the chicken has been evaluated by the appearance of membrane immunoglobulins on cells in the spleen, the thymus, the bursa and the bone marrow during enbryonic development and shortly after hatching. The majority of the bursa cells acquire demonstrable membrane immunoglobulin between days 16 and 18 of incubational age and show significantly increased amounts of membrane immunoglobulin between days 18 and 20, even though immunoglobulin-bearing cells can be found in the bursa as early as day 14 of enbryonic age. The spleen shows cells possessing immunoglobulin receptors can their membranes (Ig+) only after the bursa cells have reached full membrane immunoglobulin maturation as reflected in the number of Ig+ cells and the amounts of membrane immunoglobuline. The thymus is practically devoid of Ig+ cells in the embry and it is not clear whether there any Ig-+ cells in the bone marrow. There are two phenomena which stand out in the observations. One is that there appears to be a gradual increase in the quantity of quality of the surface immunoglobulins on individual cells with advance in the embryonic development as reflected in the gradual increase in the staining intensity. The other is that there appears to be a polar distribution of membrane immunoglobulin in some cells especially in younger embryos. This polar distribution is seen under conditions where immunoglobulin capping is prevented by inhibitors and where immunoglobulin capping is impossible, such as with monomeric Fab. Immunoglobulin capping has been found to occur readily in embryonic cells and under conditions which would normally inhibit capping in adult cells.

Five types of lymphocytes (Ig-theta-, Ig-theta+weak, Ig-theta+strong, Ig+theta- and Ig+theta+) characterized by double immunofluorescence and electrophoretic mobility. Organ distribution in normal and nude mice.

The simultaneous detection of Ig and theta on the surface of mouse lymphocytes permits the detection of four cell types (Ig-theta-, Ig-theta+, Ig+theta-, and Ig+theta+) which also have distinct electrophoretic profiles. All types are present in variable proportions in all lymphoid organs studied. Results obtained in congenitally athymic nude mice and in T-deprived mice define a new type of lymphocyte, the Ig-theta+weak. This cell is non-recirculating, Ig-, with a low density of theta and a slow electrophoretic mobility. It is a candidate for a T-committed prethymic cell.