Normal human plasma contains a complex of two proteins that are important in hemostasis and coagulation. The factor VIII procoagulant protein (antihemophilic factor) and the factor VIII-related protein (von Willebrand factor) are under separate genetic control, have distinct biochemical and immunologic properties, and have unique and essential physiologic functions. While the nature of their interaction and the details of the biochemical structures remain to be determined, the information now available permits a preliminary understanding of the molecular defects in hemophilia and von Willebrand's diseases.

This report attempts to review the present state of research on embryonic hemoglobins in humans and other mammals from a cytologic, molecular, and clinical point of view. In all mammals, the yolk sac is the site responsible for the "primitive" erythropoiesis, which produces an erythroid population characterized by peculiar cytologic features and globin gene expression. Morphological and molecular events that underlie prenatal erythropoiesis are described herein giving rise to questions regarding biology at large (i.e., the differential activity of genes capable of similar functions); molecular biology of eukaryotic genes (i.e., globin gene organization and structural subtleties); and clinical hematology (i.e., syndromes associated with the appearance of embryonic hemoglobins.

The discovery of T-cell growth factor (TCGF) has made it possible to now routinely grow in tissue culture normal and neoplastic human T cells for long periods and in large amounts. TCGF has been recently purified. It is a small protein released by a subset of mature T cells following lectin-antigen activation, which in turn acts upon other T-cell subsets that have developed specific receptors for TCGF after lectin-antigen stimulation. Thus, release of TCGF and development of receptors for it appear to be obligatory for the clonal expansion of all activated T cells. Unlike normal T cells, neoplastic T cells respond directly to TCGF, requiring no prior in vitro lectin-antigen activation. This has led to the development of several new cell lines from patients with T-cell leukemias and lymphomas. In some cases, these cells become independent of exogenous TCGF by producing their own growth factor, implying a role for TCGF in the continuous proliferation of these cells. These developments necessitate a reevaluation of some concepts of immunoregulation of T-cell activities in terms of production and response to TCGF. In addition, this information has clinical implications. Recent results have shown that a major defect of the athymic nude mouse is the inability to produce TCGF and that some immunosuppressive agents, such as glucocorticosteroids and cyclosporin-A, exert their effects on T cells by disrupting the TCGF-T-cell interaction. Some human immune deficiencies might be due to a failure to respond to or to produce TCGF, which in some cases might be corrected by exogenous TCGF.

Measurement of plasma levels of two secreted platelet proteins (beta-thromboglobulin and platelet factor 4) has been suggested as a means for detecting increased platelet activation in vivo. A crucial question in the measurement is the distinction between in vivo and in vitro secretion of the proteins. One approach to this distinction is the measurement of both proteins in each sample. These proteins are present in platelets in similar amounts and are released in similar quantities, but the plasma levels of beta-thromboglobulin exceed the plasma levels of platelet factor 4. This difference in plasma level is presumably due to more rapid removal of platelet factor 4 from the plasma level, and there is suggestive evidence that the rapid removal of released platelet factor 4 is due to its binding to endothelial cells. It appears that when there is increased release of beta-thromboglobulin and platelet factor 4 in vivo, there is an increase in the ratio of plasma beta-thromboglobulin to plasma platelet factor 4 compared to that found in normal individuals, whereas when in vitro release is responsible for elevated levels, the ratio decreases. Thus measurements of both proteins in each blood sample will allow distinction between in vivo release and artefactual in vitro release.

There are many reports in the literature of blood test abnormalities occurring in patients with venous or arterial thrombosis. Most of these have not used acceptable criteria for establishing an association between thrombosis and blood tests and, therefore, their interpretation is questionable. Recently, sensitive and specific assays have been developed for the detection of products of intravascular thrombin formation, of plasmin digests of fibrin or fibrinogen and of platelet specific proteins that are released into the plasma when platelets react with stimuli. Blood abnormalities have been sought that can either predict or detect venous thrombosis. Many of the predictive tests evaluated are nonspecific acute phase reactant responses to inflammation; of these, only reduced fibrinolytic activity has been consistently reported to be associated with postoperative venous thrombosis. Hereditary antithrombin III deficiency has been consistently shown to predispose patients to venous thrombosis. Abnormalities of the plasminogen and fibrinogen molecule have also been described in patients with familial or recurrent venous thrombosis but these are rare and the association could be coincidental. Two blood tests, the fibrinopeptide A assay and the assay for fibrin/fibrinogen fragment E are highly sensitive to acute venous thromboembolism in symptomatic patients but both are nonspecific. Elevated levels of beta thromboglobulin and platelet factor 4 have been reported in patients with arterial thromboembolism but the sensitivity and specificity of these findings is presently unknown.

Granulocyte-macrophage colony stimulating factor (GM-CSF) stimulates the in vitro proliferation and differentiation of granulocytic and macrophage cells. This regulator is now known to act at other levels of hemopoietic regulation. The heterogeneity of GM-CSFs is not only related to the tissue of origin and the in vitro production method, but also to functional subclasses of the molecule that have distinct biologic specificities. Most adult mouse organs produce GM-CSF (mol wt 23,000), but a macrophage (M)-CSF has been detected in fetal conditioned medium (CM) and isolated from L-cell CM. Murine endotoxin serum appears to contain a M-CSF, GM-CSF, and G-CSF, the last of which cofractionates with a differentiation factor active on leukemic cells. Human GM-CSFs, G-CSF, and EO-CSFs active on human cells have been detected in a variety of CM, but as yet none have been purified. Again, there are subclasses of progenitor cells that respond to particular forms of human active CSFs. GM-CSF isolated from mouse lung CM stimulates multipotential progenitor cells, the initial proliferatin of progenitors in the erythroid, eosinophil, and megakaryocyte series, as well as mature cells in the GM series. While GM-CSF is also able to stimulate the differentiation of myeloid leukemic cells, other factors appear to be more potent in this respect. Information on the regulation of GM-CSF production, on the modulators of its action on specific target cells, and on its role in vivo will be required before the physiologic function of this molecule can be properly assessed.

Several human acute myeloid leukemia cell lines were recently established. These lines provide model systems to study the control of differentiation in human myelogenous leukemia and, in a broader framework, the controls of normal myeloid development. The K562 line is composed of undifferentiated blast cells that are rich in glycophorin and may be induced to produce fetal and embryonic hemoglobin in the presence of hemin. The KG-1 cell line is composed predominantly of myeloblasts and promyelocytes. A unique characteristic of the KG-1 cells is their almost complete dependence on colony-stimulating factor for proliferation in soft-gel culture. The HL-60 is a promyelocytic leukemia cell line. In the presence of DMSO, the cells mature into granulocytes. Both the KG-1 and HL-60 cells differentiate into nondividing mononuclear phagocytes when exposed to phorbol esters. Investigations with these cell lines, and selected variants should provide important insights into the cell biology and perhaps therapy of human leukemia.

Adult autoimmune throbocytopenic purpura (ATP) is a platelet disorder that develops in certain individuals with a genetic as well as sex (female) predisposition following an environment event (?viral). This results in the production of an IgG antiplatelet antibody capable of reacting with the host's platelets, as well as crossing the placenta. This leads to the rapid clearance and destruction of opsonized platelets by the reticuloendothelial system, particularly the spleen, by greater than tenfold the normal rate. Bound platelet IgG correlates with disease severity, whereas serum antiplatelet IgG does not. It has not been rigorously established whether bound platelet IgG is directed against a platelet antigen or represents an immune complex bound to the platelet Fc receptor. Nevertheless, several lines of evidence suggest that antiplatelet IgG binds directly to a platelet antigen(s). Megakaryocyte number, volume, and mass are increased commensurate with increased platelet turnover. Platelets of increased size, megathrombocytes, are noted on peripheral smear or via platelet volume distribution analysis. Megathrombocyte number is proporationate to megakarocyte number and to platelet turnover. Megathrombocyte diameter is inversely proportional to platelet survival. Antiplatelet antibody is also associated with qualitative platelet functional defects, which are indistinguishable from those noted with thrombopathia (i.e., apparent platelet release defect). Antibody-induced functional defects are probably more common than quantitative thrombocytopenic defects and may represent a significant portion of those women with the "easy bruising" syndrome and normal platelet count. Adults who develop ATP generally develop the chronic variety, which remains permanently with the patient. Treatment should be directed towards maintaining the patient free of purpura, not restoring the platelet count to normal. This can generally be accomplished with a platelet count of > 40,000/cu mm with patients having this disorder. Approximately 50% of patients respond to steroids by a significant elevation of platelet count and improvement of purpura. However, cessation of therapy results in eventual relapse if the disease is of the chronic variety. Splenectomy is successful in approximately 65-75% of patients, resulting in a restoration of the platelet count to normal or safe levels by removing a major source of platelet destruction as well as antibody production; platelet survival improves. At least 50% of patients "in remission" following steroids or splenectomy generally have a compensated thrombocytolytic state in which increased platelet production keeps up with increased platelet destruction. Antiplatelet IgG can often be found in the serum of these patients. Patients refractory to steroids and/or splenectomy present with a serious therapeutic problem. Immunosuppressive therapy is effective in approximately one-third of refractory patients, but often relapses occur, requiring maintenance therapy with potentially mutagenic drugs...

Since granulocyte transfusions first became widely used in clinical medicine, there have been advances in the treatment of acute leukemia and improvement in prevention and management of infection in neutropenic patients. Improved understanding now exists concerning prognosis of infections in such patients, and advances have been made in procurement of granulocytes. Granulocyte transfusions should be given for specific indications, and used adjunctively to other established antiinfective therapy. Once initiated, transfusions should be given in adequate doses at daily intervals (at least) with ongoing evaluation and periodic reassessment of the whole antiinfective program. Serious complications of granulocyte transfusion therapy are relatively rare, but the physician should be prepared to manage them intelligently. Research continues in discerning exactly how granulocyte transfusion work, in preservation of granulocytes, and in delineation of immunologic phenomena affecting the efficiacy of such therapy. Granulocyte transfusions will continue to be important in the management of acute leukemia, and other reversible bone marrow failure states, and in marrow transplantation and autotransplantation.

The fast-acting and physiologically most important inhibitor of plasmin in human plasma is a recently discovered and purified alpha 2-glycoprotein with a molecular weight of 65,000-70,000 daltons occurring at a concentration of 1 muM. The inhibitor rapidly forms a completely inactive 1:1 stoichometric complex with plasmin through reaction with the B chain (light chain) of the enzyme, which contains the active center. It also reacts with trypsin and very slowly with urokinase and with some other enzymes in purified systems, but its role in vivo as an inhibitor of proteases other than plasmin seems negligible. Antiplasmin is the only plasma protein that can inhibit the fibrinolysis associated with transformed or malignant cells. The plasmin-antiplasmin complex contains neoantigenic structures not present in the parent molecules that may form the basis of immunochemical methods for detecting activation of the fibrinolvtic system in blood.