Recent advances in molecular genetics have permitted detailed study of the human alpha-globin genes and the causes of alpha-thalassemia. In this review, we examine the causes of alpha-thalassemia in the black population and the consequences of the interactions between alpha-thalassemia and structural hemoglobin variants.

Iron has been recognized as a potent hematinic since the inception of hematology as a clinical discipline. Even ancient civilizations believed in the beneficial effects of medicinal iron. Nevertheless, the precise functional liabilities of iron lack remain the subject of continuing debate. The consequences of iron deficiency, particularly from a socioeconomic standpoint, are especially important in light of its high global prevalence. A recent review of the literature indicates that approximately 30% of the estimated world population of nearly 4.5 billion are anemic, and at least half of these, 500 to 600 million people, are believed to have iron deficiency anemia.

Platelets were obtained from patients with various hyperlipidemias [type II, type V, lecithin-cholesterol acyltransferase (LCAT) deficiency] and hypolipidemias (abetalipoproteinemia, Tangier disease) to ascertain relationships among plasma lipids, platelet lipids, thrombin binding and thrombin-induced platelet aggregation, and to compare these data with those previously obtained on stimulus-response coupling in platelets following in vitro modification of membrane microviscosity. Washed platelets were studied for their ability to bind 125I-thrombin in the range of 10(-10) to 10(-6) mol/L (10 mU/mL to 100 U/mL) and to aggregate with thrombin at concentrations less than 10(-9) mol/L (100 mU/mL). The values for binding and aggregation in eight patients from six kindred with familial hypercholesterolemia, taken as a group, fell in the low normal range. If divided into two groups, patients with overt cardiovascular disease bound normal amounts of thrombin but were more responsive to it, whereas patients without overt cardiovascular disease bound lower amounts of thrombin but gave an aggregation response in the normal range. These results suggest that platelet hyperresponsiveness in familial hypercholesterolemia arises from an alteration in the coupling mechanism between thrombin binding and response such that platelets from patients with familial hypercholesterolemia are able to respond with lower receptor occupancy than is the case with normal platelets. Thrombin binding and aggregation were within normal ranges for platelets from abetalipoproteinemia patients (N = 4) and type V hyperlipoproteinemia (N = 2), although in the latter case the response appeared to be less at very low thrombin concentrations (less than 30 mU/mL). Thrombin binding was elevated in Tangier disease (N = 3) but with lower responsiveness at lower thrombin concentrations. Thrombin binding was also elevated in LCAT deficiency (N = 2), and one patient showed increased and another showed decreased aggregation responses. In general, increased plasma cholesterol levels resulted in increased stimulus-response coupling (type II), whereas increased triglyceride levels resulted in decreased coupling (type V, Tangier), and there was no apparent alteration in the coupling mechanism with overall reduction in plasma lipid levels as in abetalipoproteinemia.

In this review the genomic structure and the RNA transcripts of the alpha and beta chain of the T cell antigen receptor have been discussed. Studies of the structure of TcR beta in hematologic malignancies have revealed rearrangement in almost all of the T cell malignancies and a small proportion of non-T cell malignancies. In addition, clonal involvement of T cells in diseases such as Hodgkin's disease, angioimmunoblastic lymphadenopathy, and chronic T cell lymphocytosis have been observed. The study of the structure of the TcR beta gene is thus a useful tool for identifying clonal expansions of cells and in conjunction with studies of the immunoglobulin gene structure, and cell surface markers a useful tool for identifying cell lineage. At the present time the evaluation of the structure of the alpha chain genes has not been as fruitful. However, chromosome translocations involving the TcR alpha chain genes have been recognized and, in one case, this rearrangement has been in association with a known oncogene. With the isolation of more probes to the alpha chain region it should be possible to test its utility in identifying clonal populations and cell lineage. The recent isolation of the gamma gene of the T cell will also permit such studies. Preliminary results of studies carried out with a probe to the gamma chain gene of the T cell have paralleled results obtained with the TcR beta probe (unpublished observation).

Important insights into leukocyte differentiation and the cellular origins of leukemia and lymphoma have been gained through the use of monoclonal antibodies that define cell surface antigens and molecular probes that identify immunoglobulin and T cell receptor genes. Results of these studies have been combined with markers such as surface membrane and cytoplasmic immunoglobulin on B lymphocytes, sheep erythrocyte receptors on T lymphocytes, and cytochemical stains. Using all of the above markers, it is now clear that acute lymphoblastic leukemia (ALL) is heterogeneous. Furthermore, monoclonal antibodies that identify B cells, such as the anti-B1 and anti-B4 antibodies in combination with studies of immunoglobulin gene rearrangement, have demonstrated that virtually all cases of non-T-ALL are malignancies of B cell origin. At least six distinct subgroups of non-T-ALL can now be identified. T-ALL is subdivided by the anti-Leu-9, anti-Leu-1, and antibodies that separate T lymphocyte subsets into three primary subgroups. Monoclonal antibodies are also useful in the subclassification of non-Hodgkin's lymphoma, and certain distinct markers can be correlated with morphologic classification. The cellular origin of the malignant Reed-Sternberg cell in Hodgkin's disease remains uncertain. A substantial number of investigators favor a myelocyte/macrophage origin based on cytochemical staining; however, consistent reactivity with antimonocyte reagents has not been demonstrated. Although monoclonal antibodies are useful in distinguishing acute myeloid from acute lymphoid leukemias, they have less certain utility in the subclassification of acute myelogenous leukemia (AML). Attempts to subclassify AML by differentiation-associated antigens rather than by the French-American-British (FAB) classification are underway in order to document the potential prognostic utility of surface markers. Therapeutic trials using monoclonal antibodies in leukemia and lymphoma have been reported. Intravenous (IV) infusion of unlabeled antibodies is the most widely used method; transient responses have been demonstrated. Antibodies conjugated to radionuclides have been quite successful in localizing tumors of less than 1 cm in some studies. Therapy trials with antibodies conjugated to isotopes, toxins, and drugs are currently planned. Purging of autologous bone marrow with monoclonal antibodies and complement in vitro has been used in ALL and non-Hodgkin's lymphoma; preliminary data suggest that this approach may be an effective therapy and may circumvent many of the obstacles and toxicities associated with in vivo monoclonal antibody infusion.

Rapid progress has occurred recently in characterizing the molecular nature of the specific glycoprotein colony-stimulating factors (CSFs) controlling the proliferation; and some functional activities of granulocytes and monocyte-macrophages. All four known murine CSFs have been purified, and cDNAs for two have been cloned and expressed by mammalian and bacterial cells. Similarly, three human CSFs have been purified, and cDNAs for two cloned and expressed. This work has opened up the exciting prospects of testing the effects of these recombinant CSFs on hematopoiesis in vivo. Each CSF has a broader range of hematopoietic target cells than previously suspected, and it is now clear that the CSFs are not simply proliferative stimuli but can also regulate the functional activity of mature cells. There are increasing reasons to believe that these CSFs will be useful therapeutic agents in stimulating hematopoietic regeneration in leukopenic states and the functional activity of granulocytes and monocytes in infections.

An increasing number of reports document instances in which individual leukemic cells coexpress markers normally believed to be restricted to a single lineage. This has been interpreted by McCulloch and colleagues as aberrant programming or lineage infidelity and contrasts with earlier suggestions that lineage fidelity of gene expression was usually maintained in leukemia. We argue that several examples of infidelity are suspect on technical grounds, whereas others are bona fide and require explanation, eg, partial rearrangements and expression of Ig heavy-chain and/or T cell receptor genes in inappropriate cells and terminal deoxynucleotidyl transferase in leukemic myeloblasts. Individual examples of truly aberrant gene expression may well occur in leukemia but with insufficient regularity to be of general significance. We suggest that verifiable and consistent examples of apparent lineage infidelity do not reflect genetic misprogramming but rather the existence of a transient phase of limited promiscuity of gene expression occurring in normal biopotential or multipotential progenitors and able to be preserved as a relic in leukemic blast cell populations that are in maturation arrest. This alternative explanation has interesting implications for mechanisms of hematopoietic differentiation and leads to some testable predictions.

T gamma lymphocytes are those lymphocytes that express receptors for both the Fc portion of IgG and sheep erythrocytes. A very high proportion of normal T gamma lymphocytes are large granular lymphocytes (LGL), the cell responsible for most, if not all, natural killer (NK) and antibody-dependent cell-mediated cytotoxicity (ADCC) in humans, rats, and mice. In general, these cells are large lymphocytes with prominent azurophilic granules in the cytoplasm. Recently, a group of lymphoproliferative disorders made up predominantly of T gamma lymphocytes has been described. The most common and best studied of these disorders we refer to as "chronic T gamma-lymphoproliferative disease" (T gamma-LPD). In most cases, this disease represents the abnormal expansion of LGL, which is reflected by an increase in functionally active NK or ADCC effector cells. The chronic T gamma-LPD lymphocytes are generally characterized as E- and EA-rosette positive, acid-phosphatase, and beta-glucuronidase positive and express the pan-T antigens OKT3/Leu-4, OKT11/Leu-5, the suppressor-associated antigens OKT5,8/Leu-2, and the NK-associated antigens Leu-7/HNK-1. Typically, the patients are older, predominantly males and characteristically have a lymphocytosis of predominantly T gamma lymphocytes with lymphocyte infiltration of the bone marrow and often the spleen. While chronic T gamma-LPD is not usually an aggressive disease, the patients are often neutropenic and have recurrent bacterial infections requiring antibiotic therapy. Some patients have benefited from cytotoxic chemotherapy., but most patients have not required chemotherapy. An experimental LGL leukemia in F344 rats appears morphologically, functionally, and clinically similar to the human chronic T gamma-LPD and serves as an experimental model for further examining the ontogeny and function of LGL and may be applicable for exploring new and more effective means for the treatment of patients with chronic T gamma-LPD.