The effect of exercise on lymphocyte redistribution and leucocyte function in asymptomatic HIV-infected subjects

This study was undertaken to examine the responsiveness of circulating leucocyte and lymphocyte populations to the physiological demands of exercise in asymptomatic HIV-infected subjects with CD4+ counts greater than 500/microliter. Thirteen subjects infected with HIV and 14 control subjects underwent 20 min of defined moderate exercise at estimated 65% of their maximal ventilatory capacity on a bicycle ergometer. Blood samples were obtained for serum cortisol, norepinephrine, lymphocyte subsets (CD4, CD8, CD19, CD16-CD56), and phagocytic function at rest immediately after exercise and 20 min following the cessation of the exercise. The HIV-infected subjects had increased circulating concentrations of CD8 cells (p = .007) and CD16-CD56+ NK cells (p = .02) in response to the exercise, whereas the control group did not. There was a greater increase in monocyte respiratory burst activity following recovery from exercise in the control subjects (p = .016) but not in the HIV-infected subjects. The control subjects experienced an increase in serum cortisol in response to the exercise (p = .006), but the HIV-infected subjects did not. Our results show that the changes in the distribution and function of circulating leucocytes and adrenal neuroendocrine responses to moderate exercise differ in asymptomatic HIV-infected and control subjects.

Flow cytometric analysis of platelets from children with the Wiskott-Aldrich syndrome reveals defects in platelet development, activation and structure

The pathophysiology of platelet dysfunction in the Wiskott-Aldrich immune deficiency syndrome (WAS) remains unclear. Using flow cytometry, we have characterized the functional properties of platelets from 10 children with WAS. Patients with WAS had thrombocytopenia, small platelets, increased platelet-associated IgG and reduced platelet-dense granule content. Levels of reticulated 'young' platelets were normal in the WAS patients. Although the mean numbers of platelet glycoprotein (GP) Ib, GPIIbIIIa and GPIV molecules per platelet appeared lower in WAS patients than in healthy controls, analysis of similar-sized platelets revealed the mean number of GPIb molecules per platelet to be comparable in patients and normal controls. Surface GPIIbIIIa and GPIV expression was, however, significantly lower on the WAS platelets than on normal platelets. Compared with normal platelets, WAS platelets showed a reduced ability to modulate GPIIbIIIa expression following thrombin stimulation. In addition, thrombin- and ADP-induced expression of CD62P and CD63 was defective in WAS platelets. Phallacidin staining of the WAS platelets revealed less F-actin content than in normal platelets. Together, these data suggest that the reduced platelet number and function in WAS reflects, at least in part, a defect in bone marrow production as well as an intrinsic platelet abnormality.

Binding of thrombin to the G-protein-linked receptor, and not to glycoprotein Ib, precedes thrombin-mediated platelet activation

The roles of the G-protein-linked thrombin receptor and platelet glycoprotein Ib (GPIb) as alpha-thrombin-binding sites on platelets remain controversial. alpha-Thrombin has been proposed to bind to both GPIb and the hirudin-like domain of the G-protein-linked receptor (from which it cleaves the NH2-terminal extracellular domain to release a 41-mer peptide (TR-(1-41), where TR is alpha-thrombin receptor)) to initiate platelet activation. Using affinity-purified rabbit anti-human TR-(1-41) IgG and immunoblotting, we demonstrated TR-(1-41) release from platelets suspended in Tyrode's buffer containing 2 mM CaCl2 and incubated with >/=0.5 nM alpha-thrombin for 10-60 s at 37 degrees C. As quantified by enzyme-linked immunosorbent assay, 0.32-0.59 nM TR-(1-41) was released from washed platelets (5 x 10(11) platelets/liter) after their incubation with 10 nM alpha-thrombin for 10 s. Parallel binding of alpha-thrombin to and activation of the platelets were confirmed by flow cytometry. A monoclonal antibody against the hirudin-like domain of the G-protein-linked receptor abrogated alpha-thrombin binding to platelets, cleavage of TR-(1-41), and platelet activation by </=1.0 nM (but not 10 nM) alpha-thrombin. Proteolysis of platelet GPIb with Serratia marcescens protease or O-sialoglycoprotein endopeptidase had no effect on alpha-thrombin binding to platelets or their subsequent activation. In contrast, chymotrypsin, which cleaves both GPIb and the G-protein-linked receptor, abrogated alpha-thrombin binding to platelets, TR-(1-41) release, and platelet activation. Furthermore, monoclonal antibodies directed against the reported alpha-thrombin-binding site on GPIb inhibited neither alpha-thrombin binding to nor activation of the platelets. Thus, alpha-thrombin binds to and cleaves the G-protein-linked receptor when it activates platelets, and GPIb does not appear to serve as an important binding site when alpha-thrombin activates platelets.

Platelet and immune responses to oral cyclic dexamethasone therapy in childhood chronic immune thrombocytopenic purpura

OBJECTIVE

To examine the effectiveness of cyclic oral high-dose (HD) dexamethasone therapy in pediatric patients with chronic immune thrombocytopenic purpura (ITP), which has been reported to cause complete remission in adults with chronic ITP.

STUDY DESIGN

Eleven children with primary chronic ITP, with a median disease duration of 28 months (range, 6 to 120 months), were treated with cycles of HD dexamethasone therapy.

RESULTS

Excellent short-term responses (initial platelet counts < or = 50 x 10(9)/L, increasing to > 100 x 10(9)/L within 72 hours of completion of an HD dexamethasone cycle) were observed in 78% of 41 cycles. Long-term effects include one complete response (platelet count > or = 150 x 10(9)/L) and three partial responses (platelet count > or = 50 and < 150 x 10(9)/L) in 11 children followed for 6 or more months after completing cyclic HD dexamethasone therapy. Because side effects were substantial, three children did not complete their sixth treatment cycle. At day 6 of treatment, B lymphocytes were significantly increased (p = 0.005).

CONCLUSIONS

Dexamethasone, given orally in high doses, is an effective drug in achieving short-term platelet responses, but it induced long-term remissions in fewer than half of the children with well-established chronic ITP. Its effect on B lymphocytes requires further elucidation. A prospective, controlled study will be needed to establish whether cyclic HD dexamethasone therapy can alter the natural history of children with early chronic ITP and thus avoid splenectomy.

Platelet-surface glycoproteins in healthy and preeclamptic mothers and their newborn infants

Preeclampsia, a common complication of pregnancy, contributes significantly to maternal and fetal morbidity and mortality. It may lead to both quantitative and qualitative defects of maternal and neonatal platelets. In this prospective study, flow cytometry has been used to study expression of platelet-surface glycoproteins (GPs) on maternal and neonatal platelets of both healthy and preeclamptic subjects. We studied 15 preeclamptic women, 20-44 y of age, and their newborns (median gestational age, 32 wk; range, 26-38) and seven healthy women (aged 26-41 y) and their healthy newborns (median gestational age, 38 wk; range, 38-42). Compared with their healthy and preeclamptic mothers, resting platelets from neonates expressed significantly less CD41 and CD9. Thrombin activation resulted in significant increases in platelet-surface expression of CD62P, CD63, CD41, CD9, and CD36 in neonates and their healthy mothers. Compared with neonates of healthy mothers, platelets from neonates of preeclamptic mothers expressed lower levels of CD62P, CD63, CD9, and CD36 on activated platelets. These findings suggest that preeclampsia influences the expression of platelet-surface GPs on neonatal and maternal platelets, which may affect platelet function, leading to an additional risk for bleeding in thrombocytopenic neonates of mothers with preeclampsia.

Recipient humoral immunity against leukoreduced allogeneic platelets is suppressed by aminoguanidine, a selective inhibitor of inducible nitric oxide synthase

Leukoreduced allogeneic platelet transfusions have been previously shown to initially stimulate an in vitro cellular cytotoxicity and subsequently Induce the formation of immunoglobulin G (IgG) antidonor alloantibodies. To further characterize these responses and determine if they are related, recipient BALB/c H-2d mice were treated with aminoguanidine (AMG), a selective inhibitor of inducible nitric oxide synthase (iNOS), and transfused weekly with 2 x 10(8) C57BL/6 H2b platelets. In control, non-AMG-treated mice, transfusion significantly (P < .01) increased serum levels of interferon-gamma (IFN-gamma) by day 1 posttransfusion (PT). IFN-gamma returned to pretransfusion levels by day 3 PT, and its production was not affected by AMG treatment. Serum interleukin-4 (IL-4), on the other hand, was undetectable before and during the transfusion protocol. By day 3 PT, recipient spleen cells could mediate in vitro anti-P815 (auto), anti-EL4 (allo), and anti-R1.1 (third-party MHC) cytotoxicity, and these responses were maximal by day 7 PT. Concurrently, a significant reduction in the vitro ability of recipient splenocytes to respond to Concanavalin A (ConA) was observed; this was not seen with lipopolysaccharide (LPS) stimulation. Elevated levels of NO2- were found in the ConA culture supernatants from transfused mice at day 3 PT. Serum antidonor alloantibodies were detected by the fifth platelet transfusion. AMG treatment of recipient mice significantly inhibited the transfusion. Induced cytotoxicity and ConA-stimulated NO2- production, and restored ConA-induced proliferation to normal levels. AMG appeared to selectively inhibit platelet-induced alloantibody production in that it did not affect antibody production induced by transfusions with 10(5) allogeneic leukocytes or by immunization with a foreign protein antigen, human gamma globulin, in adjuvant therapy. These results indicate that an in vivo AMG-sensitive mechanism is essential for recipients to initiate a humoral IgG immune response against allogeneic platelets.

Characterization of platelet-reactive antibodies in children with varicella-associated acute immune thrombocytopenic purpura (ITP)

Biochemical analyses were performed on blood samples obtained from two children (P1, P2) who presented with acute immune thrombocytopenic purpura (ITP) following a recent varicella zoster virus (VZV) infection. Patient sera had antibodies that were reactive with normal blood-group O platelets as measured by flow-cytometric assay. Western blot analysis of electrophoretically separated normal blood-group O platelets under reducing and non-reducing conditions demonstrated that these sera were reactive with platelet antigens of approximately 50 and approximately 110 kD, respectively. These 50/110 kD antigens were not reactive with seven sera from acute ITP patients whose illness was not preceded by VZV infection, with serum from a patient with a prior history of VZV and no thrombocytopenia, nor with normal healthy control sera. VZV antibodies (IgG and IgM), isolated from patient sera by affinity chromatography using immobilized purified VZV glycoproteins, were found to bind to gel-filtered autologous platelets and with normal blood-group O platelets, as analysed by flow cytometry. No binding was observed using antibodies similarly prepared from healthy volunteer sera. To investigate their ability to sensitize platelets to complement activation, affinity-purified VZV antibodies were incubated with platelets and then with purified complement components C1 and 125 I-labelled C4. Platelets reacted with VZV-specific antibodies from the two patients and showed increases of 2.3-2.4-fold of platelet-surface deposition of 125 I-C4b, compared to controls. These data provide evidence that virus-specific antibodies occurring in children with varicella-associated acute ITP cross-react with normal platelet antigens, and may contribute to platelet clearance.

A survey of red cell use in 45 hospitals in central Ontario, Canada

BACKGROUND

The purpose of this survey was to establish baseline information on blood component use in relation to patient diagnoses, procedures, and demographics and to identify patterns of blood use that may be used for blood program planning and transfusion audits.

STUDY DESIGN AND METHODS

A cross-sectional survey of the transfusion of blood components in teaching and nonteaching hospitals in central Ontario between September 1991 and August 1992 was carried out. Coders of hospital medical records routinely record demographics, procedures, diagnoses, and other relevant information. A protocol was created by which medical records coders could add the components transfused to the discharge abstract for this study. Red cell use is reported here.

RESULTS

Of the 61 hospitals invited to participate, from which 547,279 patients were discharged during the 12-month period of the study, 45 (74%) agreed to participate. Information was collected on 439,373 discharged patients. Of these, 26,611 (6.1%) received at least 1 unit of red cells. Of a total of 101,116 red cell units transfused, more than 74 percent were used in patients discharged with neoplasms, gastrointestinal diseases, circulatory system diseases, and trauma. High-transfusion-use procedures included operations and procedures on the digestive and cardiovascular systems, diagnostic and therapeutic procedures, musculoskeletal system, and hemic or lymphatic system procedures.

CONCLUSION

This survey provides baseline blood transfusion information for a specific period that can help determine the need for hospital audits and maximum surgical blood-order schedule guideline reviews. This information is relevant to current recommendations to reduce patient's exposure to blood components. These transfusion data will assist in blood program planning based on known disease trends, demographics, and population changes.

Control mechanisms in thrombin generation

Thrombin accelerates its own production by activating platelets (and perhaps other cells) to provide coagulant surfaces on which prothrombinase, the enzyme complex that activates prothrombin in plasma and consists of equimolar factor Xa (serine protease) and factor Va (cofactor), assembles in a Ca(2+)-dependent reaction. Thrombin also activates factor V to provide the cofactor for factor Xa in prothrombinase, and factor VIII to provide the cofactor for factor X activation by factor IXa. Even when factor X activation is initiated by tissue factor, efficient propagation of factor X activation is critically dependent on intrinsic tenase (the factor IXa and factor VIIIa enzyme complex). These procoagulant actions of thrombin explain why good antithrombins can inhibit both intrinsic and extrinsic prothrombin activation. Because of the low level of thrombin (1 nM) required to initiate platelet activation and the activation of platelet-bound factor V, only highly efficient antithrombins, such as hirudin, can abrogate platelet-dependent prothrombinase assembly.

Differences in serum cytokine levels in acute and chronic autoimmune thrombocytopenic purpura: relationship to platelet phenotype and antiplatelet T-cell reactivity

Patients with both acute and chronic autoimmune thrombocytopenic purpura (AITP) have in vitro lymphocyte defects in the form of platelet-stimulated proliferation and cytokine secretion. A blinded study was performed to determine if these defects are related to serum cytokine levels and/or platelet antigen expression. Compared with controls, 53% of children with chronic AITP, but only 9% of those with acute AITP, had increased serum interleukin-2 (IL-2), interferon-gamma, and/or IL-10; however, none of the patients had detectible serum levels of IL-4 or IL-6, cytokine patterns suggesting and early CD4+ Th0 and Th1 cell activation. In children with chronic AITP, the levels of serum IL-2 correlated with in vitro platelet-stimulated IL-2 production. Few (17%) patients with AITP showed platelet activation, as measured by CD62 expression, or abnormal expression levels of platelet membrane glycoprotein (GP) IIbIIIa, but abnormal GPIb levels were observed in one-third of children with AITP. In contrast to normal controls and patients with nonimmune thrombocytopenia, a significant number of children with acute (80%), chronic (71%), or chronic-complex (55%) AITP and GPIb+ peripheral blood cells expressing HLA-DR. HLA-DR was variably coexpressed on distinct smaller and larger-sized GPIb+ cell populations with CD41, CD45, CD14, CD80, and/or glycophorin molecules. GPIb+ cells isolated from spleens of patients with chronic AITP had high expression (49% +/- 30%) of HLA-DR and splenic T cells had a high level of in vitro platelet-stimulated IL-2 secretion compared with controls. Platelet HLA-DR expression correlated inversely with platelet count, but not with therapy, serum cytokines, or in vitro lymphocyte antiplatelet reactivity. The results indicate that platelet HLA-DR expression is a common occurrence in patients with immune thrombocytopenia, whereas a large subpopulation of children with chronic AITP can be identified by increased serum cytokine levels and in vitro platelet-stimulated IL-2 secretion by lymphocytes, suggesting that differences exist in the immune pathogenesis of acute and chronic AITP, particularly at the level of platelet reactive T cells.

Activities of novel aryloxyalkylimidazolines on rat 5-HT2A and 5-HT2C receptors

Using transfected NIH 3T3 mouse fibroblast cell lines expressing the rat 5-HT2A and rat 5-HT2C receptor subtypes, and techniques of 2-[125I](+)-iodolysergic acid diethylamide ([125I]LSD) binding and serotonin (5-hydroxytryptamine, 5-HT)-stimulated phosphoinositide hydrolysis, we have characterized a new structural class of 5-HT receptor ligands, the aryloxyalkylimidazolines. These compounds were found to be potent competitors of [125I]LSD binding at both receptor subtypes (Ki approximately 5-200 nM) and to have efficacy ranging from potent competitive antagonists (IC50 approximately 25 nM) to moderately potent full agonists (EC50 approximately 200 nM). Some of these compounds are agonists at both receptor subtypes, while others are 5-HT2C receptor agonists with 5-HT2A receptor antagonist activity. None of the aryloxyalkylimidazolines reported here have 5-HT2A or 5-HT2C receptor selective antagonist activity. Since these compounds are novel structures, we compared them with a variety of reference 5-HT receptor ligands selected from other chemical classes that have previously been studied at 5-HT2A and 5-HT2C receptors in native tissues.

Plasmin accelerates platelet-dependent prothrombinase formation without activating the platelets

Patients with acute myocardial infarction who undergo thrombolytic therapy may shortly thereafter present evidence for increased platelet activation and thrombin activity, and recurrent thrombosis. This study investigated whether plasmin activates platelets and prothrombin in recalcified platelet-rich plasma (RPRP) to cause (at least in part) these side-effects of thrombolytic therapy. Plasmin (0.1 and 1.0 CU/ml) addition to RPRP with microM r-tick anticoagulant peptide (the latter a factor Xa inhibitor which abrogates prothrombin activation by prothrombinase at the concentration used) resulted in no change in the concentration of prothrombin fragment 1 + 2, or in the expression of GMP-140, the resting and activated GP IIb-IIIa conformers, and GPIb on platelets. Thus, plasmin neither activates platelets nor prothrombin in RPRP. However, plasmin accelerated platelet activation and secretion, and prothrombin fragment 1 + 2 production in RPRP. When combined with 1 microM r-tick anticoagulant peptide and 1 or 10 mM alpha-thrombin to RPRP, plasmin also increased the number of GMP-140 molecules expressed/platelet without enhancing alpha-thrombin binding to the platelets. Additionally, plasmin accelerated prothrombin activation when it was added to washed platelets resuspended in factor V depleted plasma simultaneously with 10 mM CaCl2, 10 nM alpha-thrombin for 10 s (to activate platelets and platelet factor V), followed by 4 microM hirudin and 1 nM factor Xa. Thus, plasmin potentiates the platelet release reaction in response to alpha-thrombin (probably by increasing the availability of factor V on the platelets) to enhance prothrombin activation in RPRP. These actions of plasmin may contribute to the increased platelet activation and thrombotic side-effects that can occur after thrombolytic therapy.

Applications of flow cytometry in the analysis of blood leukocytes

Flow cytometric analysis of blood leukocytes is currently used for both routine clinical measurements as well as for cutting edge research applications. This technology has enabled rapid and accurate determination of leukocyte antigens and quantitative analysis of leukocyte subsets, tests of leukocyte function, determination of the presence of antineutrophil and antilymphocyte antibodies in plasma and on cells, measurement of CD34+ hematpoietic stem cells in peripheral blood and bone marrow samples, measurement of apoptosis, and detection of virus-infected leukocytes. This review will focus on the use of the flow cytometer for investigations of blood leukocytes in transfusion medicine.

Analysis of platelets by flow cytometry

Transfusion medicine has become a multi-disciplinary field with many recent technical developments and the flow cytometer has had a significant impact in transfusion medicine, especially at the level of platelet immunobiology. Many routine tests in platelet immunology are now performed by flow cytometry laboratories, including assessment of platelet-associated allo- and auto-antibodies and complement components. Platelet analysis by flow cytometry has been applied to detection of platelet antigens, platelet surface-bound proteins, platelet activation, measurement of reticulated platelets, intracellular calcium studies, and the measurement of platelet microparticles in vivo and in vitro. This review will focus on the use of the flow cytometer in these applications in investigations of platelet immunology.

Flow cytometric evaluation of platelet activation in blood collected into EDTA vs. Diatube-H, a sodium citrate solution supplemented with theophylline, adenosine, and dipyridamole

With platelet activation, there is modulation of platelet surface molecule expression. In flow cytometric analyses of in vivo platelet activation, results are often confounded by activation induced in vitro by the preparative procedures. It is particularly important therefore to prevent or retard platelet activation as soon as possible after withdrawal of the blood sample. Taking blood into paraformaldehyde, or fixing the cells with paraformaldehyde as soon as possible after withdrawal, has been employed to prevent platelet activation in vitro, but paraformaldehyde-fixed platelets cannot be further used in functional studies. We investigated the efficacy of Diatube-H, a commercially available combination of platelet antagonists (theophylline, adenosine, and dipyridamole), in preventing or retarding platelet activation in vitro, along with its effects on modulation of platelet membrane glycoproteins (GP) and adhesion molecules. In contrast to blood taken into EDTA, blood taken into Diatube-H vacutainer tubes could be stored at room temperature for up to 4 hr prior to paraformaldehyde fixation without significant in vitro platelet activation, as measured by CD62P, CD63 and modulation of GPIb and GPIIbIIIa surface expression. Hence, paraformaldehyde fixation could be deferred for several hours, permitting transport of samples from distant sites. Studies of thrombin-induced platelet activation indicated that platelets taken into Diatube-H remained functional i.e. were able to be activated. Expression of the CD29, CD49b and CD31 adhesion molecules on the platelet surface was unaffected by storage in Diatube-H. The results suggest that Diatube-H may be a useful reagent for flow cytometric studies of platelets when the samples cannot be processed immediately.

A randomized, double-blind comparison of methoxamine and epinephrine in human cardiopulmonary arrest

The beneficial effect of epinephrine has been attributed to its alpha-adrenergic properties. The present study was designed to compare the effects of epinephrine and methoxamine in witnessed cardiac arrests. Consecutive, witnessed cardiac-arrest victims presenting to the emergency room or from the inpatient population of our institution were enrolled in this study. Patients were randomized to receive either epinephrine (2 mg bolus followed by 2 mg every 4 min) or methoxamine (40 mg bolus followed after 4 min by 40 mg) in a blind design. Patients were followed prospectively for survival and neurologic outcome. A total of 199 patients were randomized into the study, but 54 had to be retrospectively dropped from analysis for failure to comply with the study protocol. Of the 145 patients remaining, 77 received methoxamine (M) and 68 epinephrine (E). There was no difference in rate of successful resuscitation (42% versus 53%, M versus E, respectively), or in neurologic outcome as measured by the Glasgow-Pittsburgh Coma Score (GPCS). This study failed to demonstrate any difference in the rate of initial resuscitation, survival to discharge from the hospital, or neurologic status with methoxamine as opposed to epinephrine in the setting of cardiac arrest.

Indirect allorecognition of platelets by T helper cells during platelet transfusions correlates with anti-major histocompatibility complex antibody and cytotoxic T lymphocyte formation

To study the cellular immunology of platelet-induced alloimmunization, a murine transfusion model was developed. BALB/c (H-2d) recipient mice were transfused weekly with 2 x 10(8) platelets or 10(3) leukocytes from C57BL/6 (H-2b) donor mice. Recipient antidonor major histocompatibility complex (MHC) class I alloantibodies could be detected in flow cytometric assays by the fifth platelet transfusion. In contrast, when leukocytes only were transfused, alloantibodies were not detected. In vitro assays demonstrated that murine H-2b platelets were positive for MHC class I expression but lacked MHC class II molecules on their membranes and were unable to stimulate proliferation or cytokine production when incubated with naive H-2d spleen cells. In vivo, however, platelet transfusions induced two distinct patterns of cell-mediated reactivity. First, during the initial transfusions and before alloantibody formation, there was induction of T-cell anergy, characterized by the inability of recipient T cells to respond to Concanavalin A (ConA) or to proliferate in an antidonor mixed lymphocyte reaction (MLR), together with suppressed natural killer (NK) cell activity. This unresponsiveness was associated with a transient increase in nitric oxide (NO)-dependent cytotoxicity and interleukin-1 (IL-1) production. Second, once alloantibodies developed, significantly increased antidonor CD8+ cytotoxic T lymphocyte (CTL) and NK cell responses were observed. At this time, when recipient spleen cells were depleted of CD8+ T cells and incubated with only donor platelets in 7-day antigen-presenting cell (APC) assays, enhanced proliferation and IL-2 production occurred. These cellular responses were not seen when 10(3) allogeneic leukocytes were transfused. Thus, the results suggest that leukoreduced platelet transfusions induce antidonor MHC antibodies and CD8+ CTL responses in recipient mice. At the same time, the transfusions induced recipient CD4+ T-cell activation when incubated with donor platelets in the presence of syngeneic APCs, an indirect recognition pathway that correlates with the time of alloantibody production.

Platelet activation in warm and cold heart surgery

Recent studies suggest that patients undergoing warm heart surgical procedures have reduced postoperative bleeding. To determine if this is due to differences in platelet activation, we measured platelet membrane glycoproteins (GPIb, GPIIb/IIIa, GMP 140), platelet fragments, and platelet counts before, during, and after normothermic (37 degrees C) or hypothermic (28 degrees to 30 degrees C) cardiopulmonary bypass. Cardiopulmonary bypass was associated with a significant decrease in platelet count, platelet membrane GPIb, and platelet fragments, and an increase in GMP 140 (p < 0.05). Normothermic cardiopulmonary bypass induced an early significant increase in granulocytes, whereas this was delayed until after rewarming in the hypothermic group. Mean 24-hour postoperative blood loss was 786 +/- 226 mL in the cold group versus 547 +/- 56 mL in the warm group (p = not significant). We conclude that cardiopulmonary bypass affects platelet activation and integrity and that these changes are similar in direction and magnitude for hypothermic and normothermic techniques.

Programmed cell death induced by HIV type 1 antigen stimulation is associated with a decrease in cytotoxic T lymphocyte activity in advanced HIV type 1 infection

The immune competence of peripheral blood mononuclear cells (PBMCs) from human immunodeficiency virus-seropositive (HIV+) patients was studied by assessing cytotoxic T lymphocyte (CTL) activity following recall HIV antigen stimulation. Target cells were HLA-A-matched EBV-transformed B cells expressing HIV-1 antigen. In the presence of recombinant IL-2 (rIL-2, 2 or 10 U/ml), about 50% of PBMCs from HIV+ asymptomatic patients responded to HIV-1 antigen stimulation in vitro with increased cytotoxic activity. In contrast, PBMCs from patients with overt AIDS, cultured in medium containing rIL-2 (2 U/ml) and HIV-1 antigen, showed no increase in cytotoxic activity; in the presence of rIL-2 (10 U/ml) and HIV-1 antigen, an inhibitory effect on CTL activity was observed. This inhibitory effect was associated with programmed cell death (apoptosis) of CD8+ lymphocytes and cells of both gamma/delta TcR-positive and -negative phenotypes. However, prior to the apoptosis, different TcR phenotypes of T lymphocyte reacted differently to HIV-1 antigen stimulation. The HIV-1 antigen initially appeared to cause gamma/delta TcR-positive T lymphocytes to proliferate and/or differentiate and later induced cell death. Whereas, prior to the apoptosis, no proliferation of gamma/delta TcR-negative T lymphocytes induced by HIV-1 antigen was observed.

The effect of rabbit antithymocyte serum (RATS) and OKT3 on peripheral blood mononuclear cell subsets following renal transplantation

Fifty-five renal transplant recipients were studied prospectively for changes in monoclonal antibody-defined mononuclear cell subsets (MCS) over the first 45 days posttransplant. Patients received induction immunotherapy with either monoclonal OKT2(n = 29) or polyclonal RATS (n = 26) preparation. Sequential examinations showed characteristic patterns of MCS depletion, which differed according to the type of therapy received and which subset was examined. In general, induction therapy with RATS resulted in greater and more sustained reduction of most MCS than was seen with OKT3 therapy. In recipients who received OKT3 induction there was a correlation between allograft rejection and an increase in lymphocytes expressing pan-T cell markers and in natural-killer cells. In contrast, rejection episodes in patients receiving RATS were associated with increases in subpopulations of T cells including helper, inducer and suppressor/cytotoxic T-cell subsets. There was no correlation of rejection with B cells or T-cell activation markers. The different patterns of MCS depletion with different antilymphocyte preparations and the association between changes in different MCS and rejection warrant further investigation.

Thrombin binding to platelets and their activation in plasma

The interactions of alpha-thrombin with platelets are critical in haemostasis and arterial thrombosis. This study established methods for characterizing the binding of alpha-thrombin to platelets and some of its consequences in platelet-rich plasma. The binding of alpha-thrombin to platelets and the subsequent platelet activation were quantified by flow cytometry, using affinity purified polyclonal antibodies to human alpha-thrombin and a monoclonal antibody to GMP-140, respectively. Dose-dependent binding of alpha-thrombin to platelets and their activation occurred in parallel, both reaching the maxima for each enzyme concentration within 10s after > or = 1.0 nM alpha-thrombin was added to recalcified PRP containing 1 microM recombinant tick anticoagulant peptide. The tick anticoagulant peptide abrogated prothrombin activation in the platelet-rich plasma. alpha-Thrombin binding to platelets, and their activation, were abrogated by a monoclonal antibody to the hirudin tail-like domain of the seven transmembrane thrombin receptor on platelets. Therefore this receptor represents an important site for alpha-thrombin binding to platelets suspended in plasma. D-Phe-Pro-ArgCH2-alpha-thrombin only bound to platelets when its concentration was > or = 100 nM, and it did so without inhibiting platelet activation by alpha-thrombin. Whereas concentrations of hirudin equimolar to those of alpha-thrombin failed to abrogate alpha-thrombin-mediated activation of platelets, a 10-fold molar excesses of hirudin over alpha-thrombin abrogated alpha-thrombin binding to platelets. The demonstration that > or = 1.0 nM alpha-thrombin can bind to platelets and initiate their activation raises the possibility that the levels of thrombin generated in venous and arterial thrombosis contribute to platelet activation in vivo.