Orientation and specificity of fibrin protofibril binding to ADP- stimulated platelets

We have investigated the molecular basis of platelet:fibrin binding by studying interactions between platelets and protofibrils, soluble two- stranded polymers of fibrin, which are intermediates on the fibrin assembly pathway. The specificity of these interactions was examined with transmission electron microscopy (TEM), which clearly showed thin fibers with lengths to 150 nm attached to the cell surface of normal, stimulated platelets. Immunogold electron microscopy using rabbit anti- human fibrinogen as the first stage antibody verified the identity of the surface-bound molecules, and the immunogold distribution paralleled that observed with the fibrin/fibrinogen molecules alone. Contacts between the ends of the fibers and the platelets were frequently observed, but lateral contacts were also evident. Given the diameter at the point of fibrin contact (18.2 +/- 1.3 nm), it is possible that several glycoprotein receptors were involved in binding each protofibril. Morphometric analyses demonstrated that normal platelets stimulated by ADP in the absence of exogenous fibrin(ogen) or in the presence of fibrin protofibrils and antibodies directed against the GPIIb/IIIa complex lacked this molecular layer on the surface. Neither protofibrils nor fibrin fibers adhered to the surface of Glanzmann's thrombasthenic platelets, as demonstrated by TEM and microfluorimetry. Synthetic peptides of sequence RGDS and HHLGGAKQAGDV effectively blocked the binding of protofibrils to the surface of normal, stimulated platelets while synthetic GHRP had no effect. These results provide direct evidence for multiple points of attachment between fibrin protofibrils and the glycoprotein IIb/IIIa complexes present in a functional conformation on the surface of normal, stimulated platelets.     

K562 cells produce and respond to human erythroid-potentiating activity

Human erythroid-potentiating activity (EPA) is a 28,000 mol wt glycoprotein that stimulates the growth of erythroid progenitors in vitro and enhances colony formation by the K562 human erythroleukemia cell line. EPA has potent protease inhibitory activity, and is also referred to as tissue inhibitor of metalloproteinases (TIMP). We observed that colony formation by K562 cells in semi-solid medium containing reduced fetal calf serum (FCS) is not directly proportional to the number of cells plated, suggesting production of autostimulatory factors by K562 cells. Using radioimmunoprecipitation and a bioassay for EPA, medium conditioned by K562 cells was found to contain high levels of biologically active EPA; Northern hybridization analysis confirmed the expression of EPA mRNA. Radiolabeled EPA was used to identify cell surface receptors on K562 cells. Together, these results suggest that EPA may act as an autocrine growth factor for K562 cells.     

Molecular cloning of the cDNA for human erythrocyte beta-spectrin

Overlapping cDNA clones, totaling 3.3 kilobases (kb) in length, which encode over 50% of the human erythrocyte beta-spectrin subunit, were isolated by antibody screening of a lambda gt11 expression library constructed from human fetal liver mRNA. The amino acid sequence of the C-terminus of beta-spectrin was derived. The size of beta-spectrin mRNA in human erythroleukemia cells was found to be 7.5 kb. Erythrocyte beta- spectrin is encoded by a gene located on human chromosome 14, as determined by cDNA hybridization to human X mouse somatic cell hybrids.     

DNA ligation in relation to DNA strand breaks in phytohemagglutinin- stimulated blast cells from acute lymphoblastic and nonlymphoblastic leukemia

DNA ligase activity was determined in the WBCs from 306 cases of acute lymphoblastic leukemia (ALL) and acute nonlymphocytic leukemia (ANLL). In T-ALL cells this activity was either low or absent. DNA analysis by nucleoid, alkaline elution, and alkaline sucrose centrifugation after cells were embedded in agarose inserts has shown more DNA breaks in T- ALL than in ANLL blasts. Phytohemagglutinin stimulation of T-ALL blasts resulted in the apparent joining of the DNA breaks. Apparent identical results can be obtained by the incubation of DNA with exogenous DNA ligase. The authors suggest that this enzyme is a crucially regulated step of replication and subsequent proliferation in this type of leukemia.     

In vivo effect of human erythroid-potentiating activity on hematopoiesis in mice

Endotoxin-free purified recombinant human erythroid-potentiating activity (EPA) was administered to normal and bled mice. In anemic ICR mice EPA treatment led to a significant increase in the number of reticulocytes in the peripheral blood and erythroid precursors in the spleen. Stimulation of CFU-E and BFU-E in the spleen was also observed in C3H/HEJ mice, which excluded the possibility of endotoxin effect. Unchanged, 51Cr-tagged red cell survival and lack of radioactivity in the stool or urine suggests that the EPA stimulation of erythropoiesis was not due to hemolysis or bleeding. Thus, EPA has an effect on erythropoiesis in anemic mice in vivo.     

Chikungunya fever: General and oral healthcare implications

Chikungunya virus (CHIKV) was first isolated in humans in 1952, following an epidemic in Tanzania. The origin of the name means “to bend forward or become contorted,” in reference to the posture adopted by patients due to the joint pain that occurs during the infection. Epidemiology data suggest that by the end of 2015, about 1.6 million people had been infected with CHIKV. The acute period of the disease is characterized by high fever, myalgia, joint pain, and severe and disabling polyarthritis, sometimes accompanied by headache, backache, and maculopapular rash, predominantly on the thorax. Around half of the patients will progress to the subacute and chronic phases, that is manifested by persistent polyarthritis/polyarthralgia, accompanied by morning stiffness and fatigue, which could remain for years. Oral features may include gingivitis possibly as a consequence of arthralgia of the hands leading to limited oral health measures as well as burning sensation and oral mucosal ulceration. Treatment in the acute phase includes acetaminophen, and weak opioids (tramadol or codeine) should be used in cases of severe or refractory pain. For patients who have progressed to the subacute stage and who have not had notable benefit from common analgesics or opioids, NSAIDs, or adjunctive pain medications (anticonvulsants or antidepressants) may be of benefit. In patients with moderate‐to‐severe musculoskeletal pain or in those who cannot be given or tolerate NSIADs or opiates, prednisolone should be prescribed.     

Zika virus: oral healthcare implications

Zika virus (ZIKV) infection has been recognised since 1947, but just recently it became a worldwide major public health problem. The most common features of ZIKV infection are fever, cutaneous rash, arthralgia and conjunctivitis but most affected patients with the clinical disease present with only mild symptoms. However, severe neurological complications have been described: there is an occasional association with Guillain–Barre syndrome, and emerging data indicate an association between vertical transmission of ZIKV infection and microcephaly, but no specific orofacial manifestations have yet been reported. ZIKV is present in body fluids and has also been demonstrated in the saliva, but there is as yet no reliable evidence to support ZIKV transmission via this pathway. Transmission in oral health care should be effectively prevented using standard infection control measures. There are currently no specific treatments for Zika virus disease and no vaccines available, so prevention of ZIKV is based on vector control.