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.

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A new cell line, HD-Mar, was established from a pleural effusion of a patient with Hodgkin's lymphoma. Formation of E rosettes, sensitivity to anti-T serum, elevated terminal deoxynucleotidyl transferase activity, presence of T-cell and the common ALL membrane antigens, morphology, and cytochemical staining indicate that the HD-Mar line is of thymic derivation. Absence of any immunoglobulin determinants, the lack of EBNA or any other EBV-associated antigen or function are also characteristics associated with established T-cell-derived lymphoma cell lines. Karyotype analysis indicated a tetraploid origin of the cell line.

A modified antiglobulin test, based on the high affinity between the Fc portion of the red blood cell (RBC) bound IgG and the Fc receptor on the myeloid cell K-562, was utilized for demonstration of immunoglobulins (Ig) on thalassemic RBC. Ig was found on the RBC of 73 out of 80 patients with thalassemia. The immunoglobulins on the thalassemic RBC belonged to the IgG subclass and were autoreactive. Elution studies utilizing various carbohydrates, or by thermal stripping, indicated that at least part of the IgG molecules found on the thalassemic RBC were specifically reactive with terminal galactosyl residues on the RBC membrane. IgG antibodies with similar reactivity were also demonstrated in normal human serum. These natural antigalactosyl IgG antibodies from normal sera could bind to IgG- depleted thalassemic RBC. Thalassemic RBC and normal senescent RBC were previously found to contain reduced amounts of membrane sialic acid (SA). It is suggested that the antigalactosyl IgG antibodies interact with newly exposed galactosyl residues underlying the sialic acid units. Such interaction may lead to the shortened lifespan of thalassemic RBC and may result in sequestration of senescent normal RBC by the reticuloendothelial system.

Leukemic cells from the peripheral blood of 52 patients with acute and chronic leukemias were incubated with 12-0-tetradecanoyl phorbol ester (TPA). Thirty-one cases of lymphocytic leukemia (18 cases of acute lymphoblastic and 13 cases of chronic lymphocytic leukemia), 13 cases of acute nonlymphoblastic (myelo or myelomonoblastic) leukemia, and eight cases of blastic crisis of CGL (seven cases of predominantly myeloblastic crisis, and one case of lymphoblastic crisis) were studied. In all cases of lymphoid leukemia, cells formed clumps or aggregates after exposure to TPA, while in all cases of myeloid leukemia cells became adherent to the substrate. Seven of the eight cases of blastic crisis of CGL were predominantly myeloid in type and cells adhered to the substrate, while in a single case of lymphoid crisis in CGL cells formed clumps after TPA exposure. Functional, cytochemical, and ultrastructural studies showed altered cell differentiation and continuing in vitro maturation of leukemic cells after exposure to TPA. In the light of the above results, it is concluded that this simple test employing TPA exposure in vitro serves as a reliable means of distinguishing blasts from different origins in human leukemias.