Pneumococcal vaccines for sickle cell disease.

BACKGROUND: People with sickle cell disease are particularly susceptible to pneumococcal infection, which may be fatal. Infants (children aged up to 23 months) are at particularly high risk, but conventional polysaccharide pneumococcal vaccines may be ineffective in this age group. New conjugate pneumococcal vaccines are now available, which may help to reduce the incidence of infection in people with sickle cell disease. OBJECTIVES: To determine the efficacy of pneumococcal vaccines for reducing morbidity and mortality in people with sickle cell disease. SEARCH STRATEGY: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group trials register, comprising of references identified from comprehensive electronic database searches and hand searching relevant journals and abstract books of conference proceedings. In addition, we contacted relevant pharmaceutical companies and experts in the field.Date of most recent search of Group's trials register: November 2003. SELECTION CRITERIA: All randomised and quasi-randomised controlled trials comparing a polysaccharide or conjugate pneumococcal vaccine regimen with a different regimen or no vaccination in people with sickle cell disease. DATA COLLECTION AND ANALYSIS: Two reviewers independently selected studies for inclusion, extracted data and assessed trial quality. MAIN RESULTS: Nine trials were identified in the searches and five trials, with a total of 547 participants, met the inclusion criteria. Only one trial reported incidence of pneumococcal infection, and this demonstrated that the polysaccharide pneumococcal vaccine used (PPV14) failed to significantly reduce the risk of infection in children under three years of age, but was associated with only minor adverse events. Three trials of conjugate pneumococcal vaccines found that immune response was increased compared to control groups, including in infants, although clinical outcomes were not measured in these trials. REVIEWER'S CONCLUSIONS: Previous trials have shown that conjugate pneumococcal vaccines are safe and effective in normal healthy patients, even those under the age of two years. The controlled trials included in this review have demonstrated immunogenicity (the body's response, without which there is no protection) of these vaccines, and observational studies in people with sickle cell disease support these findings. We therefore recommend that conjugate pneumococcal vaccines are used in people with sickle cell disease. Randomised trials in patients with sickle cell disease will be needed to determine the optimal vaccination regimen when further, potentially more effective vaccines become available. Such trials should measure clinical outcomes of effectiveness.

Autoantibody formation in the alloimmunized red blood cell recipient: clinical and laboratory implications.

Alloimmunization to erythrocyte antigens is a well-characterized complication in heavily transfused patients. Less well recognized, however, is the frequency of autoantibody formation in these previously alloimmunized patients. The autoantibodies are heterogeneous and of variable clinical significance. We describe the clinical history, laboratory evaluation, diagnosis, and treatment in 4 patients who developed autoantibodies in temporal association with alloantibody formation. In one case, the autoantibody found on routine screening had no clinical significance. In another case, the autoantibody made accurate blood typing and subsequent transfusion exceedingly difficult. Two patients experienced hemolysis as a consequence of the autoantibody. The management of both patients included supportive measures, while one patient required glucocorticosteroids and red blood cell transfusion. We review the published literature concerning autoimmunization in the transfused alloimmunized host. The spectrum of clinical consequences is important for the general practitioner to recognize, as these complications may occur during routine blood transfusions.

Management of a patient with a mechanical aortic valve and antibodies to both thrombin and factor V after repeat exposure to fibrin sealant.

We describe a patient who developed a markedly prolonged PT, PTT, and thrombin time 13 days after repeat exposure to fibrin sealant during coronary artery bypass grafting and aortic valve replacement. Evaluation revealed an inhibitor to bovine thrombin that cross-reacted with human thrombin. In addition an inhibitor to human coagulation factor V was identified. Despite coagulation abnormalities there was no evidence of bleeding. Nevertheless, effective anticoagulation was required to minimize the thrombotic complications associated with the patient's prosthetic valve. We elected to take a conservative approach and not utilize pharmacologic anticoagulation until there was diminution in the effect of the acquired inhibitors. We report on our patient's course and review the available literature addressing the management of patients demonstrating inhibitors to blood coagulation factors after repeat exposure to fibrin sealants.

Cloning, expression, sequence analysis, and characterization of streptokinases secreted by porcine and equine isolates of Streptococcus equisimilis.

Streptokinases secreted by nonhuman isolates of group C streptococci (Streptococcus equi, S. equisimilis, and S. zooepidemicus) have been shown to bind to different mammalian plasminogens but exhibit preferential plasminogen activity. The streptokinase genes from S. equisimilis strains which activated either equine or porcine plasminogen were cloned, sequenced, and expressed in Escherichia coli. The streptokinase secreted by the equine isolate had little similarity to any known streptokinases secreted by either human or porcine isolates. The streptokinase secreted by the porcine isolate had limited structural and functional similarities to streptokinases secreted by human isolates. Plasminogen activation studies with immobilized (His)(6)-tagged recombinant streptokinases indicated that these recombinant streptokinases interacted with plasminogen in a manner similar to that observed when streptokinase and plasminogen interact in the fluid phase. Analysis of the cleavage products of the streptokinase-plasminogen interaction indicated that human, equine, and porcine plasminogens were all cleaved at the same highly conserved site. The site at which streptokinase was cleaved to form altered streptokinase (Sk*) was also determined. This study confirmed not only the presence of streptokinases in nonhuman S. equisimilis isolates but also that these proteins belong to a family of plasminogen activators more diverse than previously thought.

Species specificity of plasminogen activation and acquisition of surface-associated proteolytic activity by group C streptococci grown in plasma.

Our laboratory previously demonstrated that group C streptococcal isolates from humans and horses secrete streptokinases that preferentially activate plasminogens reflecting the origin of the isolates. To analyze the significance of these findings, series of streptokinase-producing Streptococcus equisimilis isolates recovered from humans and horses were examined. Southern blot analysis revealed that chromosomal DNA of the streptococcal isolates from humans reacted exclusively with a skc(hu) probe and that chromosomal DNA of streptococcal isolates from horses reacted preferentially with an skc(eq) probe in a distinct pattern. The streptococcal isolates were examined for the ability to acquire surface-bound plasmin-like activity when grown in the presence of human or equine plasma. Each of eight isolates from humans acquired significant enzymatic activity only when grown in the presence of human plasma, while each of eight isolates from horses acquired activity only when grown in the presence of equine plasma. Analysis of bacterial and host protein requirements indicated critical roles for streptokinase, activatable plasminogen, and fibrinogen. These requirements may explain why certain streptococcal isolates cause disease only in a limited number of mammalian hosts.

Ischemic colitis and acquired resistance to activated protein C in a woman using oral contraceptives.

We present the case history of a 22-yr-old woman diagnosed with ischemic colitis associated with the use of oral contraceptives (OC). At the time of her presenting symptoms activated protein C (APC) resistance, a risk factor for thrombosis, was demonstrated. There was no laboratory evidence of inherited thrombophilia; that is, antithrombin III, protein C and protein S levels were normal and the factor V Leiden mutation was not present. The OC were discontinued and the patient's symptoms improved. Subsequent evaluation revealed that the activated protein C resistance had resolved. This case illustrates APC resistance as a potential link between OC use and its known association with ischemic colitis.

Chronic relapsing thrombotic thrombocytopenic purpura and antiphospholipid antibodies: a report of two cases.

We report on 2 cases of chronic relapsing thrombotic thrombocytopenic purpura, in which anti-phospholipid antibodies were also found. The first patient was felt to have the anti-phospholipid antibody syndrome, while the second patient had anti-phospholipid antibodies without clinical manifestations of the anti-phospholipid antibody syndrome. We discuss chronic relapsing thrombotic thrombocytopenic purpura and the anti-phospholipid antibody syndrome. Furthermore, we introduce the possibility of an association between chronic relapsing thrombotic thrombocytopenic purpura and the presence of anti-phospholipid antibodies.

Plasminogen activation by invasive human pathogens.

In this review the interaction between invasive human pathogens expressing plasmin(ogen) receptors and/or producing plasminogen activators with the human plasmin(ogen) system is described. Evidence is presented for multiple mechanisms by which human pathogens can acquire a surface bound form of plasmin that cannot be regulated by host serpins. The potential importance of these pathways in providing the organisms with the ability to cross tissue barriers is discussed.

The plasmin-binding protein Plr of group A streptococci is identified as glyceraldehyde-3-phosphate dehydrogenase.

Group A streptococci bind the serine protease plasmin with high affinity. Previously, a 41 kDa protein was identified as a candidate plasmin receptor protein (Plr) from group A streptococcal strain 64/14. The plr gene encoding Plr was cloned and the deduced amino acid sequence of Plr had significant similarity to glyceraldehyde-3-phosphate dehydrogenases (GAPDHs). In this study we have isolated cytoplasmic GAPDH of streptococcal strain 64/14. This enzyme was examined, on both structural and functional levels, for its relatedness to the Plr of strain 64/14 purified from mutanolysin extract and to recombinant Plr. We report here that no differences were detected between streptococcal Plr and cytoplasmic GAPDH on the basis of antibody reactivity, plasmin-binding activity, GAPDH activity, N-terminal amino acid sequence, peptide map analysis by V8 protease digestion and amino acid composition analysis. Furthermore, the plr gene appears to be present as a single copy in group A streptococci.

Analysis of the interaction of group A streptococci with fibrinogen, streptokinase and plasminogen.

Group A streptococci demonstrate a number of distinct ways to interact with the human fibrinolytic system to acquire unregulatable cell-surface enzymatic activity. Interactions between bacteria, fibrinogen, streptokinase and plasminogen resulted in acquisition of cell-associated enzymatic activity that can lyse fibrin clots despite the presence of the major physiological plasmin inhibitor, alpha 2-antiplasmin. Western blot analysis of extracted streptococcal surface proteins suggested that binding of fibrinogen to M or M-related proteins mediated the capture of streptokinase-plasminogen complexes to the bacteria. The enzymatic complex formed by reaction of bacteria with fibrinogen, streptokinase and plasminogen was found to be more stable in human plasma than pre-formed plasmin bound directly to the same bacteria strain.

A role for fibrinogen in the streptokinase-dependent acquisition of plasmin(ogen) by group A streptococci.

Acquisition of plasmin(ogen) by group A streptococci occurs by two distinct pathways. In addition to the well-characterized direct interaction of plasmin with cell-surface receptors on group A streptococci, a second pathway dependent on streptokinase and a nonplasminogen factor(s) present in human plasma was identified. The role of streptokinase in the second pathway was not merely as a plasminogen activator, since substitution of the plasminogen activator urokinase did not result in the capture of plasmin(ogen) by bacteria in the presence of plasminogen-depleted plasma. However, if streptokinase was added to plasmin that had been generated by treatment of plasminogen with urokinase, the ability of the bacteria to capture plasmin in the presence of plasminogen-depleted plasma was restored. Fibrinogen present in human plasma was identified as the major factor required for streptokinase-dependent uptake of plasmin(ogen) by group A streptococci.

Characterization of a novel streptokinase produced by Streptococcus equisimilis of non-human origin.

Streptokinases are proteins with plasminogen activator activity produced by certain hemolytic streptococci. We previously identified equine streptococcal isolates which produced streptokinases (ESKs) that bound both human and equine plasminogen but only readily activated equine plasminogen (14). This property was exploited to purify a representative ESK produced by Streptococcus equisimilis strain 87-542-W. Affinity chromatography with human plasminogen resulted in the isolation of a M(r) approximately 49,000 molecule with two isoforms. This ESK was subsequently compared to well characterized streptokinases (HSKs) that efficiently activate human plasminogen. Differences in streptokinases were identified in the highly conserved amino-terminal amino acid sequence, peptide maps, and antigenic properties, and these differences were supported by DNA hybridization studies. These results indicate that the family of proteins identified as streptokinases has much greater diversity than previously appreciated.

Capturing host plasmin(ogen): a common mechanism for invasive pathogens?

Plasmin is a potent enzyme that can dissolve blood clots and degrade extracellular matrix proteins. A number of pathogenic bacteria produce plasminogen activators. Many of these organisms can also bind plasmin(ogen) to surface receptors and protect the active enzyme from physiological inhibition. Cell-surface localization of plasmin may be a common mechanism used by bacteria to facilitate movement through normal tissue barriers.

Analysis of plasmin(ogen) acquisition by clinical isolates of group A streptococci incubated in human plasma.

Group A streptococci isolated from throat swabs or blood cultures were compared for the expression of plasmin(ogen) receptors. The majority of isolates bound 125I-labeled Lys-plasmin and 125I-labeled Lys-plasminogen while displaying minimal reactivity with 125I-labeled Glu-plasminogen. All streptococcal isolates could acquire surface enzymatic activity when incubated in human plasma but not if the plasma had been depleted of plasminogen. The ability to acquire surface enzymatic activity was limited by the quantity of streptokinase in the reaction mixture. There was no statistically significant difference between group A streptococci isolated from throat swabs and those from blood cultures with respect to their interaction with components of the fibrinolytic system in human plasma. However, these isolates could be divided into two groups based on their ability to acquire surface enzymatic activity when incubated in plasma with exogenous streptokinase. Surprisingly, the acquisition of surface enzymatic activity when incubated in plasma containing streptokinase was not always correlated with the plasmin(ogen) binding capacity determined by direct binding of radiolabeled ligands. Analysis of this phenomenon suggests that group A streptococci can use diverse mechanisms to acquire plasmin(ogen)-dependent enzymatic activity.

Cloning, sequence analysis, and expression in Escherichia coli of a streptococcal plasmin receptor.

Plasmin(ogen) receptors are expressed by many gram-positive and gram-negative bacteria. We previously isolated a plasmin receptor from a pathogenic group A streptococcal strain (C. C. Broder, R. Lottenberg, G. O. von Mering, K. H. Johnston, and M. D. P. Boyle, J. Biol. Chem. 266:4922-4928, 1991). The gene encoding this plasmin receptor, plr, was isolated from a lambda gt11 library of chromosomal DNA from group A streptococcal strain 64/14 by screening plaques with antibodies raised against the purified streptococcal plasmin receptor protein. The gene was subcloned by using a low-copy-number plasmid and stably expressed in Escherichia coli, resulting in the production of an immunoreactive and functional receptor protein. The DNA sequence of the gene contained an open reading frame encoding 335 amino acids with a predicted molecular weight of 35,787. Upstream of the open reading frame, putative promoter and ribosomal binding site sequences were identified. The experimentally derived amino acid sequences of the N terminus and three cyanogen bromide fragments of the purified streptococcal plasmin receptor protein corresponded to the predicted sequence encoded by plr. The deduced amino acid sequence for the plasmin receptor protein revealed significant similarity (39 to 54% identical amino acid residues) to glyceraldehyde 3-phosphate dehydrogenases.