Mechanisms of MHC class I-restricted antigen presentation

The vertebrate immune system monitors whether an organism is invaded by pathogens. Therefore, each cell has to prove itself as healthy. This is achieved by presenting fragments of intracellular protein degradation products on the surface, i.e., each cell displays peptides on specialised proteins known as major histocompatibility complex (MHC) class I proteins. A displayed peptide has to pass certain constraints before its presentation: It has to be excised out of a protein, translocated into the endoplasmic reticulum (ER) and fit into the binding groove of a MHC molecule. In theory, alteration of the cellular protein profile by mutation or infection should force pathogen-specific T-cells to take action via recognition of foreign peptide bound to MHC class I molecules on the cell surface. Unfortunately, pathogens and tumours have evolved many ways to affect antigen presentation and to escape from immune response. Understanding the exact mechanisms of antigen presentation, i.e., protein cleavage and peptide binding by MHC molecules, would allow their manipulation by drugs and lead to the re-establishment of the correct antigen presentation pathway. This review will summarise current knowledge of the mechanisms of antigen presentation and discuss putative targets for therapeutic treatment as well as for vaccination strategies.     

Challenges of Childhood TB/HIV Management in Malawi

The diagnosis and management of childhood tuberculosis (TB) are major challenges in countries such as Malawi with high incidence of TB and human immunodeficiency virus (HIV) infection. Diagnosis of TB in children often relies only on clinical features but clinical overlap with the presentation of HIV and other HIV-related lung disease is common. The tuberculin skin test (TST), the standard marker of M. tuberculosis infection in immune competent children, has poor sensitivity in HIV-infected children and is not usually available in Malawi. HIV test should be routine in children with suspected TB as it improves clinical management. HIV-infected children are at increased risk of developing active disease following TB exposure which justifies the use of isoniazid preventive therapy (IPT) once active disease has been excluded but this is difficult to implement and appropriate duration of IPT is unknown. HIV-infected children with active TB experience higher mortality and relapse rates on standard TB treatment compared to HIV-uninfected children, highlighting the need for further research to define optimal treatment regimens. HIV-infected children should also receive appropriate supportive care including cotrimoxazole prophylaxis and anti-retroviral treatment (ART) if indicated. There are concerns about concurrent use of some anti-TB drugs such as rifampicin with some ARTs.     

Confirmation of hepatitis C infection: a comparison of five immunoblot assays

BACKGROUND: Recently, new immunoblot assays for the detection of antibodies to hepatitis C virus (HCV) became available. STUDY DESIGN AND METHODS: The performance of five confirmatory anti-HCV immunoblot assays was studied with samples with known HCV antibody and HCV RNA status. The assays were a third-generation strip recombinant immunoblot assay (RIBA-3, Chiron Corp., Emeryville, CA), a second-generation HCV blot (DB-2 blot, Diagnostic Biotechnology, Singapore), the Wellcozyme HCV Western blot (Murex blot, Murex Diagnostics, Dartford, UK), an immunodot HCV assay (Matrix, Abbott Laboratories, Chicago, IL), and the third-generation HCV line immunoassay (Liatek-III, Organon Teknika, Boxtel, The Netherlands). RESULTS: Sensitivity on samples from 48 HCV RNA-positive, second-generation RIBA (RIBA-2)-positive persons and specificity on samples from 31 low-risk donors was 96 percent or better for all assays. The sensitivity on 31 HCV RNA-positive, RIBA-2- indeterminate samples was as follows: Liatek-III, 94 percent; RIBA-3, 90 percent; Murex blot, 61 percent; Matrix, 55 percent; and DB-2 blot, 39 percent. In testing 39 HCV RNA-negative, RIBA-2-indeterminate donor samples, the percentage found to be negative was Liatek-III, 77 percent; RIBA-3, 67 percent; Murex blot, 49 percent; DB-2 blot, 33 percent; and Matrix, 15 percent. The order of sensitivity on four HCV seroconversion series was (from high to low): RIBA-3, Liatek-III, DB-2 blot, Murex blot, and Matrix; the differences were small. CONCLUSION: Detection of HCV antibodies was not refined by the addition of new HCV antigens (NS5, E2/NS1), but by improved classical antigens (core, NS3, NS4). Replacement of the commonly used RIBA-2 will resolve the status of a high proportion of RIBA-2-indeterminate samples.     

Sensitivity and specificity of four assays to detect human T− lymphotropic virus type I or type I/II antibodies

BACKGROUND: Assays that detect human T-lymphotropic virus type I and type II antibody (HTLV-I/II) are widely used in the routine screening of blood donors. STUDY DESIGN AND METHODS: Four commercially available anti-HTLV-I (Fujirebio and Organon Teknika) or -HTLV-I/II assays (Murex and Ortho) were evaluated in various serum panels: A) HTLV-I-positive specimens (n = 41), confirmed by Western blot and polymerase chain reaction; B) a commercially available anti-HTLV-I/II panel; C) serial dilutions of sera from HTLV-I-positive individuals (n = 30), confirmed by immunofluorescence assay and Western blot: D) serial dilutions of HTLV-II-positive blood donors (n = 20), confirmed by Western blot and polymerase chain reaction, and E) sera from first-time blood donors (n = 1055). RESULTS: All four assays elicited reactions in all 82 HTLV-I- positive samples in Panels A, B, and C. Of 32 HTLV-II-positive specimens in Panels B and D, 31 (96.9%) reacted in the Organon Teknika assay and all 32 reacted in the remaining tests. Probit analysis of test results in Panels C and D indicated that the Fujirebio test was the most sensitive assay, followed by Organon Teknika, Ortho, and Murex. The specificities of Fujirebio, Murex, Organon Teknika, and Ortho tests in 1055 first-time blood donors were 99.9, 100, 99.6, and 99.9 percent, respectively. CONCLUSION: All four studied assays for detecting HTLV-I or HTLV-I/II antibodies are appropriate as screening tests.     

Platelet turnover and kinetics in immune thrombocytopenic purpura: results with autologous 111In-labeled platelets and homologous 51Cr- labeled platelets differ

Mean platelet survival and turnover were simultaneously determined with autologous 111In-labeled platelets (111In-AP) and homologous 51Cr- labeled platelets (51Cr-HP) in ten patients with chronic immune thrombocytopenic purpura (ITP). In vivo redistribution of the 111In-AP was quantitated with a scintillation camera and computer-assisted image analysis. The patients were divided into two groups: those with splenic platelet sequestration (spleen-liver 111In activity ratio greater than 1.4), and those with diffuse sequestration in the reticuloendothelial system. The latter patients had more severe ITP reflected by pronounced thrombocytopenia, decreased platelet turnover, and prominent early hepatic platelet sequestration. Mean platelet life span estimated with 51Cr-HP was consistently shorter than that of 111In-AP. Platelet turnover determined with 51Cr-HP was thus over-estimated. The difference in results with the two isotope labels was apparently due to greater in vivo elution of 51Cr. Although the limitations of the techniques should be taken into account, these findings indicate that platelet turnover is not always normal or increased in ITP, but is low in severe disease. We suggest that this may be ascribed to damage to megakaryocytes by antiplatelet antibody. The physical characteristics in 111In clearly make this radionuclide superior to 51Cr for the study of platelet kinetics in ITP.     

Transcranial magnetic stimulation in patients with bipolar depression: a double blind, controlled study

Dolberg OT, Dannon PN, Schreiber S, Grunhaus L. Transcranial magnetic stimulation in patients with bipolar depression: a double blind, controlled study. Bipolar Disord 2002: 4(Suppl. 1): 94–95. © Blackwell Munksgaard, 2002     

G gamma and A gamma globin-chain biosynthesis by adult and umbilical cord blood erythropoietic bursts and reticulocytes

We examined gamma-globin-chain biosynthesis by adult and umbilical cord blood or erythropoietic bursts in methylcellulose clonal culture and gamma-chain synthesis by cord blood reticulocytes. Globin chains were labeled with 14C-amino acids and guantitated by using autoradiography or fluorography. Alpha, beta, and G gamma and A gamma chains were separated by isoelectric focusing in polyacrylamide gels containing 8 M urea and 3% Nonidet P-40 (a nonionic detergent). Time course examinations of the gamma-chains synthesized by the bursts revealed no changes in the G gamma:A gamma ratio between days 10 and 18 of culture. The ratio of G gamma/(G gamma + A gamma) in cultures of adult circulating erythroid precursors was 0.38 +/- 0.09, which corresponds to the known ratio in adult peripheral blood erythrocytes. The relative G gamma-chain biosyntheses in the cord blood bursts and reticulocytes were 0.56 +/- 0.02 and 0.66 +/- .008, respectively. Both are intermediate between the accepted newborn and adult ratios. Natal erythropoietic precursors appear to be in the transitional stage with respect to the switching of G gamma-A gamma ratios.     

Muckle–Wells syndrome in an Indian family associated with NLRP3 mutation

Muckle — Wells syndrome (MWS) is a rare autosomal dominant disease that belongs to a group of hereditary periodic fever syndromes. It is part of the wider spectrum of the cryopyrin-associated periodic syndrome (CAPS) which has only rarely been described in non-Caucasian individuals. It is characterized by recurrent self-limiting episodes of fever, urticaria, arthralgia, myalgia and conjunctivitis from childhood. Progressive sensorineural hearing loss and amyloidosis are two late complications. MWS is caused by gain of function mutations in the NLRP3 gene, which encodes cryopyrin, a protein involved in regulating the production of proinflammatory cytokines. We report two patients with MWS in an Indian family associated with the p.D303N mutation in the NLRP3 gene. These findings promote awareness of these hereditary periodic fever syndromes as a cause for recurrent fevers from childhood in the Indian population.KEY WORDS: Hereditary periodic fever, D303N mutation, Indian family, Muckle—Wells syndrome, p.D303N mutation     

Characterization of human erythroid burst-promoting activity derived from bone marrow conditioned media

Bone marrow conditioned media (BMCM) increases burst number and the incorporation of 59Fe into heme by bursts when peripheral blood or bone marrow cells are cultured at limiting serum concentrations. Burst- promoting activity (BPA) has now been purified approximately 300-fold from this source by ion-exchange chromatography on DEAE-Sephadex and absorption chromatography on hydroxyapatite agarose gel. Marrow BPA increased burst number and hemoglobin (Hb) synthesis in a dose- dependent manner. A larger increase in Hb synthesis than in burst number was consistently observed, which was probably a consequence of the increase in the number of cells per burst that occurs in the presence of BPA. The role of BPA in culture could be distinguished from erythropoietin (Ep), since no bursts grew in the absence of Ep, whether or not BPA was present, and since it had no effect on the growth of erythroid colonies scored at day 5 of culture. Our purified fraction did not support the growth of CFU-C in culture. Activity was stable at temperatures of 70 degrees C or lower for 10 min; exposure to 80 degrees C resulted in approximately 50% loss of activity. BPA was completely inactivated by treatment at 100 degrees C for 10 min. Thus, human bone marrow cells produce a heat-sensitive factor that specifically promotes the growth of early erythroid progenitors in culture.