Pathways of self-tolerance and the treatment of autoimmune diseases

JOURNAL CLUB direct connection of these structures to the central nervous system. Low concentrations of PrP sc were detected in the rectum, adrenal gland, and thymus from 1 of the 4 patients. Of interest, the buffy coat fraction of blood was negative despite the use of the highly sensitive assay. The development of improved assays for the detection of PrP s~ are important advances in our ability to understand the prevalence and routes of transmission of vCJD. This study has implications for concern over vCJD spread by surgical instruments and biopsy instruments. It also suggests that archival tonsillar material will have higher yields than appendices for investigation of the prevalence of disease. Finally, the paper provides additional reassurance that the concentration of PrP sc in blood is thousands or perhaps tens of thousands fold lower than that found in neurologic tissue. (S.D.)

Pathways of self-tolerance and the treatment of autoimmune diseases, C.G. Goodnow. Lancet 357:2115-

79 transducing a tolerogenic signal to cells, and mice with a knockout of CTLA4 die from an exuberant lymphoproliferative syndrome. Also, deficiency of Fas-ligand, FAS, or the downstream protease Caspase-10 all result in forms of autoimmune lymphoproliferative syndrome because of the loss of important inducers of apoptosis. Mice whose gene for transforming growth factor beta has been knocked out also develop a syndrome of lethal immune overactivity. The phenomenon of apoptosis is an important aspect of Goodnow's review. He points out the newly described phosphatidylserine receptor on macrophages. This receptor appears to play a key role in the phagocytosis of apoptotic cells. Activation of this receptor leads to enhanced expression of transforming growth factor beta, which promotes a tolerogenic signal. In contrast, antigens released from necrotic or apoptotic cells that complex with heat shock proteins appear to trigger dendritic cells to express immunogeuic co-stimulatory molecules such as B7. (S.D.)

2121, 2001. This review article should interest all those who have struggled to keep pace with the new developments in immunologic pathways that lead to either an immunogenic or a tolerogenlc immune response. Goodnow writes a clear and concise review that, although not specifically about blood transfusion, has obvious relevance to theories of a transfusion-related immunosuppressive effect. Three themes emerge from his review. First, there are rare but very informative monogenic disorders that highlight the importance of specific regulatory molecules in the immune response. Second, cells fall under the influence of both immunogenic and tolerogenic signals simultaneously and the cellular response may depend on not only the anatomic location of the stimuli but also the timing of stimuli. Ultimately, the cellular response will depend on the effect of cell signals on activation of genes that lead to either clonal expansion, no effect, or clonal deletion. Two major pathways of intracellular signaling are outlined. Immunogenlc signals result in activation of both nuclear factor of activation of T cells (NFATc) and nuclear factor kappa of B cells (NFKB)--2 nuclear transcription factors that activate clonal expansion of cells. Tolerogenic signals lead to activation of NFATc alone (without NFKB) and the transcription of genes involved in tolerance. Chronic low stimulation favors the NFATc pathway alone, whereas bolus stimulation favors simultaneous activation of both pathways. Each pathway depends on elevations of intracellular calcium as part of the second messenger pathway. Thus, blockers of the calcineurin system such as cyclosporin or FK506 interrupt both pathways. Three X-linked disorders highlight the importance of key molecules in the immunogenic pathway. Deficiency of the tyrosine kinase required to activate NFKB results in X-linked agammaglobulinemia. Congenital deficiency (or deliberate knockout) of CD40-1igand results in the X-linked hyper IgM syndrome in which there is absent IgG response and defective T-cell immunity. X-linked severe combined immunodeficiency results from disruption of the gene coding for gamma-c subunit that is shared by the cell surface receptors for IL-2, 1L-7, and IL-15. tn contrast, other single molecule deficiencies highlight the importance of specific molecules as mediators of the tolerogenie pathway. For example, CTLA4 plays an important role in

Comparison of quantitative and qualitative PCR assays for cytomegalovirus DNA in plasma, A.M. Caliendo, R. Schuurman, B. Yen-Lieberman, et al. J Clin Microbiol 39:1334-1338, 2001. Mounting evidence suggests that increased quantity of CMV DNA in the plasma of acquired immunodeficiency syndrome patients predicts CMV disease and decreased survival. Laboratories commonly use inhouse developed polymerase chain reaction (PCR)-based assays to detect and quantify the CMV DNA. Because the inhouse developed assays of individual laboratories vary in methodology and performance, the comparison of results generated in studies at different laboratories is limited. With the goal of characterizing a standardized assay to which inhouse data can be compared, Caliendo and colleagues examined the performance of commercial qualitative (AMPLICOR CMV Test, Roche Molecular Systems, Branchburg, N J) and quantitative (COBAS AMPLICOR CMV MONITOR Test, Roche Molecular Systems) CMV DNA assays, then compared the latter to an inhouse PeR-based assay used in previously published clinical studies. The AMPLICOR assays were evaluated at 3 different laboratories. The quantitative AMPLICOR assay showed greater sensitivity (at input concentration of 125 CMV copies/mL, 18/18 replicates had a viral load > 400 CMV DNA copies/mL) compared with the AMPLICOR qualitative assay (100% sensitivity at input concentration of 1,000 CMV DNA copies/mL). The authors proposed that this difference in sensitivity might be caused by the use of a greater volume of plasma in the amplification step of the quantitative assay. Both assays showed 100% specificity. The viral load measured by the AMPLICOR quantitative assay was approximately 10-fold greater than the input concentration, which was based on an electron microscopic viral particle count and did not account for free DNA. Free DNA, however, would be detected by P e R and therefore might account for the 10-fold difference. The AMPLICOR quantitative assay was linear up to 50,000 CMV DNA copies/mL and showed greater variation at lower copy numbers (SD range 0.11 to 0.48 logl0 unit at viral load < 1,000 CMV DNA copies/ml and SD of 0.15 at viral load < 10,000 CMV DNA copies/ml). Based on the results of 2 laboratories using the same lots of kits, the error (interassay) variance was greater than the lot or laboratory variance. The quantitative AMPLI-