Diagnostic accuracy of faecal occult blood tests used in screening for colorectal cancer: a systematic review.

OBJECTIVE: To determine the accuracy of guaiac and immunochemical faecal occult blood tests (FOBTs) for the detection of colorectal cancer in an average-risk screening population. METHODS: Fifteen electronic databases, the internet, key journals and reference lists of included studies were searched. We included diagnostic accuracy studies that compared guaiac or immunochemical FOBTs with any reference standard, for the detection of colorectal cancer in an average-risk adult population, with sufficient data to construct a 2 x 2 table. RESULTS: Fifty-nine studies were included. Thirty-three evaluated guaiac FOBTs, 35 immunochemical FOBTs and one evaluated sequential FOBTs. Sensitivities for the detection of all neoplasms ranged from 6.2% (specificity 98.0%) to 83.3% (specificity 98.4%) for guaiac FOBTs, and 5.4% (specificity 98.5%) to 62.6% (specificity 94.3%) for immunochemical FOBTs. Specificity ranged from 65.0% (sensitivity 44.1%) to 99.0% (sensitivity 19.3%) for guaiac FOBTs, and 89.4% (sensitivity 30.3%) to 98.5% (sensitivity 5.4%) for immunochemical FOBTs. Diagnostic case-control studies generally reported higher sensitivities. Sensitivities were higher for the detection of CRC, and lower for adenomas, in both the diagnostic cohort and diagnostic case-control studies for both guaiac and immunochemical FOBTs. CONCLUSIONS: Immudia HemSp appeared to be the most accurate immunochemical FOBT, however, there was no clear evidence to suggest whether guaiac or immunochemical FOBTs performed better, either from direct or indirect comparisons. Poor reporting of data limited the scope of this review, and the use the Standards for Reporting of Diagnostic Accuracy guidelines is recommended for reporting future diagnostic accuracy studies.

The SCF/KIT pathway plays a critical role in the control of normal human melanocyte homeostasis.

During development, the interaction of stem cell factor (SCF) with its receptor, KIT, is critical for the survival of melanocytes. Limited in vivo human studies have suggested a possible activating role of SCF on adult human melanocytes. In order to study the impact of this pathway on normal melanocyte homeostasis, human skin xenografts were treated with serial injections of recombinant human SCF or a KIT-inhibitory antibody (K44.2). On histologic evaluation, SCF injection increased, whereas KIT inhibition decreased the number, size, and dendricity of melanocytes. Immunohistochemical expression of melanocyte differentiation antigens, including tyrosinase-related-protein-1 and gp100/pmel17, was markedly increased by treatment with SCF, and decreased by K44.2 treatment. The number of Ki67-positive melanocytes was increased in the SCF-treated tissue, suggesting a direct proliferative effect of SCF; conversely, treatment with K44.2 resulted in melanocyte loss, which did not appear reversible with prolonged treatment. These findings demonstrate that the SCF/KIT pathway remains critical in adult human skin, and that pharmacologic modulation of this single pathway can control cutaneous melanocyte homeostasis.

KIT expression reveals a population of precursor melanocytes in human skin.

Human skin is believed to harbor a reservoir population of precursor melanocytes. It has been difficult to identify these putative cells experimentally, because they lack phenotypic features that define mature melanocytes. We have evaluated expression of the KIT tyrosine kinase receptor, which is critical for melanocyte development, as a possible marker of these cells. Sections of human skin were evaluated with single- and double-immunolabeling techniques. KIT-reactive dendritic cells were identified in the basal layer of the epithelia and were most numerous in the follicular infundibula and the rete ridges. These cells were located on the epithelial side of the basement membrane and lacked expression of cytokeratin and mast cell tryptase. The location of the KIT-reactive cells was distinctly different from that of Langerhans cells (identified with anti-CD1a) or Merkel cells (identified with CAM 5.2). Within the epidermis and upper follicular infundibulum the majority of the KIT-reactive dendritic cells also coexpressed TRP-1, a marker present in differentiated melanocytes. In the deeper follicular regions, the coexpression of TRP-1 in the KIT-reactive cells was absent. Throughout the epidermis and follicle, however, the KIT-reactive cells coexpressed BCL-2, a marker known to be increased in melanocytes. Thus, KIT expression reveals a population of intraepithelial cells that have immunophenotypic characteristics of mature melanocytes within the upper epithelial regions, but lack the differentiated melanocytic phenotype within the deeper follicular regions. We propose that these KIT(+), BCL-2(+), and TRP-1(-) cells constitute a precursor melanocyte reservoir of human skin.

In vitro RNA selection of an autoimmune epitope on stem-loop II of U1 RNA.

Autoantibodies to U1 RNA occur frequently in sera from patients with SLE and SLE-overlap syndromes. These autoantibodies have been previously shown to recognize major epitopes on stem-loops II and IV of U1 RNA. To further define these recognition sites, in vitro RNA selection was performed to identify the individual nucleotides which form the antibody binding site. Serum autoantibodies were used in this procedure to select synthetic variants from a library of RNA oligomers with a central region of 25 degenerate nucleotides in a linear context. A consensus sequence was derived from the autoantibody-selected RNA ligands that corresponded to a region of stem-loop II. It contained six continuous nucleotides (U63-C64-C65,-A66-X-U68) and one presumed discontinuous nucleotide (U79). In vitro selection of RNA ligands from simpler sublibraries consisting of oligomers with random loops and fixed U1 stem II sequences yielded no consensus sequence, suggesting that autoimmune recognition occurs independent of loop nucleotides. Competition assays confirmed the specificity of these binding reactions. The structural nature of this autoimmune U1 RNA epitope is compatible with a model of autoantibody production based on stimulation by native small nuclear ribonucleoprotein particles.

Specificity of autoantibodies for recombinant 60-kd and 52-kd Ro autoantigens.

OBJECTIVE: To compare patterns of Ro autoantigen recognition in primary Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE). METHODS: Sera were tested by enzyme-linked immunosorbent assay (ELISA) and immunoprecipitation for reactivity with recombinant human 60-kd and 52-kd Ro proteins. RESULTS: SLE and primary SS sera exhibited similar patterns of reactivity with the recombinant 52-kd protein. However, a greater proportion of sera from primary SS patients than from SLE patients did not react with recombinant 60-kd protein in ELISA yet precipitated its translation product in solution-phase assays. CONCLUSION: Disease state can influence recognition of the recombinant 60-kd Ro antigen.

Anti-La antibody production by MRL-1pr/1pr mice. Analysis of fine specificity.

In evaluating the origin of autoantibodies, patterns of self-Ag recognition have been interpreted to reflect the relative role of Ag in stimulating a response. Few studies, however, have assessed whether human autoantibodies display patterns of autoantigen recognition similar to those of SLE-prone mice. In previous studies, anti-La antibodies from humans have been shown to bind multiple epitopes on recombinant human La Ag, including immunoreactivity with a large fragment, termed La C, representing the middle portion of the La sequence. We report herein for the first time that MRL-1pr mice also spontaneously produce antibodies to recombinant human La protein and resemble human autoantibodies in their reactivity with La C. To further investigate the fine specificity of this response, we tested for antibody binding to six synthetic La peptides representing sequences within La C. Whereas two of the synthetic La peptides reacted with MRL-1pr sera containing anti-La binding, low reactivity was observed with a large panel of human anti-La sera. Our results therefore show that patterns of La antigen recognition displayed by MRL-1pr antibodies differ from those of human autoantibodies, possibly reflecting differences between mouse and man in the induction of these responses.

The fine specificity of anti-La antibodies induced in mice by immunization with recombinant human La autoantigen.

Because of increasing evidence suggesting that anti-La autoantibodies are induced in humans by an Ag-specific mechanism, we investigated the antibody response of animals immunized with the human La Ag and studied its relationship to the anti-La response of autoimmune patients. Anti-La antibodies were raised in 6- to 8-wk-old male MRL(-)+/+, C57BL/6J, BALB/c, and A/J mice by immunizing with authentic human La protein obtained by recombinant expression in Escherichia coli. As we have shown previously for human autoantibodies, induced mouse anti-La antibodies reacted with recombinant fusion proteins containing nonoverlapping sequences from different portions of the La molecule. The epitope specificity of antibodies to the middle region of the La Ag was further evaluated using six synthetic La peptides predicted to be antigenic based on their hydrophilic properties. Although the induced mouse anti-La antibodies bound to five of the six synthetic La peptides, human anti-La autoantibodies failed to recognize any of the peptide homologs. These results suggest that mice respond to immunization with human La protein differently than humans who develop autoimmunity to this self Ag.

Temporal correlation of antibody responses to different epitopes of the human La autoantigen.

To investigate the temporal relationship of antibody responses to different La epitopes, sequential sera from nine patients with systemic lupus erythematosus and Sjogren's syndrome were tested by enzyme-linked immunosorbent assay for antibody binding to a series of recombinant fusion proteins containing different regions of the La molecule. The results of this analysis indicate that antibody responses to four different La fragments vary in parallel over time. This finding is supported by a statistical analysis indicating that the changes in antibody levels between the six pairs of responses were highly correlated (P less than 0.001). Furthermore, we show by immunoaffinity purification that antibodies to the three nonoverlapping La protein fragments do not cross-react with other fragments and, hence, represent independent populations. These results suggest that anti-La antibodies are coordinately produced to different epitopes on the La molecule, possibly reflecting an antigen-driven mechanism.