A role for the integrin alpha6beta1 in the differential distribution of CD4 and CD8 T-cell subsets within the rheumatoid synovium.

OBJECTIVE: CD4 and CD8 T-cell subsets accumulate in distinct microdomains within the inflamed rheumatoid synovium. The molecular basis for their differential distribution remains unclear. Since chemokines and adhesion molecules play an important role in the positioning of leucocytes at sites of inflammation, we tested the hypothesis that the differential expression and function of chemokine and/or adhesion molecules explains why CD4(+) T cells accumulate within perivascular cuffs, whereas CD8(+) T cells distribute diffusely within the tissue. METHODS: Expression of an extensive panel of chemokine receptors and adhesion molecules on matched CD4(+) and CD8(+) T cells from peripheral blood (PB) and synovial fluid (SF) was analysed by multicolour flow cytometry. Migration assays and flow-based adhesion assays were used to assess the functional consequences of any differences in the expression of chemokine and adhesion receptors. RESULTS: CD4(+) and CD8(+) T cells from PB and SF expressed unique yet consistent patterns of chemokine and adhesion receptors. SF CD8(+) T cells were much less promiscuous in their expression of chemokine receptors than SF CD4(+) T cells. The alpha(6)beta(1) integrin was highly expressed on PB CD4(+) T cells, but not on PB CD8(+) T cells. Laminin, the ligand for alpha(6)beta(1), retained CD4(+) T cells, but less so CD8(+) T cells, within inflamed synovial tissue. CONCLUSION: Infiltrating PB CD4(+) T cells, but not CD8(+) T cells, express functional levels of the alpha(6)beta(1) integrin. We propose that this leads to their retention within the rheumatoid synovium in perivascular cuffs, which are defined and delineated by the expression of laminin.

Detecting antibodies with similar reactivity patterns in the HLDA8 blind panel of flow cytometry data.

The blind panel collected for the 8th Human Leucocyte Differentiation Antigens Workshop (HLDA8; ) included 49 antibodies of known CD specificities and 76 antibodies of unknown specificity. We have identified groups of antibodies showing similar patterns of reactivity that need to be investigated by biochemical methods to evaluate whether the antibodies within these groups are reacting with the same molecule. Our approach to data analysis was based on the work of Salganik et al. (in press) [Salganik, M.P., Milford E.L., Hardie D.L., Shaw, S., Wand, M.P., in press. Classifying antibodies using flow cytometry data: class prediction and class discovery. Biometrical Journal].

Classifying antibodies using flow cytometry data: class prediction and class discovery.

Classifying monoclonal antibodies, based on the similarity of their binding to the proteins (antigens) on the surface of blood cells, is essential for progress in immunology, hematology and clinical medicine. The collaborative efforts of researchers from many countries have led to the classification of thousands of antibodies into 247 clusters of differentiation (CD). Classification is based on flow cytometry and biochemical data. In preliminary classifications of antibodies based on flow cytometry data, the object requiring classification (an antibody) is described by a set of random samples from unknown densities of fluorescence intensity. An individual sample is collected in the experiment, where a population of cells of a certain type is stained by the identical fluorescently marked replicates of the antibody of interest. Samples are collected for multiple cell types. The classification problems of interest include identifying new CDs (class discovery or unsupervised learning) and assigning new antibodies to the known CD clusters (class prediction or supervised learning). These problems have attracted limited attention from statisticians. We recommend a novel approach to the classification process in which a computer algorithm suggests to the analyst the subset of the "most appropriate" classifications of an antibody in class prediction problems or the "most similar" pairs/ groups of antibodies in class discovery problems. The suggested algorithm speeds up the analysis of a flow cytometry data by a factor 10-20. This allows the analyst to focus on the interpretation of the automatically suggested preliminary classification solutions and on planning the subsequent biochemical experiments.

Origin and properties of soluble CD21 (CR2) in human blood.

By analysis with a panel of CD21 MoAbs it is shown that a large part of the soluble CD21 in human blood plasma is of the long isoform (CD21L), as judged by comparison with antigen produced by mouse L cells transfected with CD21L-cDNA and reactivity with the restricted CD21 MoAb R4/23. This is compatible with the hypothesis that soluble CD21 in the blood is mainly derived from follicular dendritic cells (FDC). Cells from a human keratinocyte cell line transfected with cDNA from the Burkitt lymphoma cell line Raji also produced soluble CD21L (sCD21L), whereas the short form of sCD21 (sCD21S) was the major component of sCD21 produced by the B lymphoblastoid cell line LICR-LON-HMy and the T cell line Jurkat. Confocal studies of FDC isolated from human tonsil revealed that CD21 was present in the cytoplasm. On gel filtration sCD21 from untreated serum has an apparent size considerably greater than the 130kD found by SDS-PAGE analysis. This may be partly accounted for by the non-globular shape of the molecule, but may also indicate, as reported by others, that in its native state sCD21 is complexed with other proteins. However, no evidence of complexing with sCD23 or C3d could be found.

Quantitative analysis of molecules which distinguish functional compartments within germinal centers.

Five zones in the secondary follicles of human tonsils are described, which are distinguished by the phenotype of their constituent cells. Moving from the apex to the base of the follicle the zones are termed: follicular mantle, outer zone, apical light zone, basal light zone and dark zone. The dark zone contains proliferating, CD77high, centroblasts and thin, widely spaced processes of follicular dendritic cells (FDC). The apical and basal light zones on the other hand contain a dense network of FDC which express CD21 and CD54 strongly. The FDC of the apical light zone differ from those of the basal light zone by their high expression of CD23. Centroblasts of the dark zone give rise to non-proliferating centrocytes which move apically through the light zone (Eur. J. Immunol. 1991. 21:2951). The centrocytes of the basal light zone are more pyroninophilic, more closely-packed and larger than those in the apical light zone. Consequently, by conventional histology the basal light zone appears to be part of the dark zone. The nomenclature adopted, however, adheres to the convention that the dark zone is filled with proliferating centroblasts. Cells undergoing apoptosis were identified both in the dark and light zones, but more than half of these cells were located in the basal light zone. This is consistent with the concept that the progeny of cells which undergo somatic mutation in their immunoglobulin variable region genes in the dark zone migrate to the light zone where they are selected on the basis of their capacity to bind to antigen held on FDC. Cells receiving an antigen-dependent signal survive while those that do not kill themselves by apoptosis. The outer zone does not contain CD23high cells and in this way is distinguished from the adjacent follicular mantle and apical light zone. It contains small lymphoid cells, blasts and plasmacytoid cells. Many cells of the outer zone express CDw75 strongly. The outer zone also extends as a narrow band around the dark zone. Possible roles of FDC and T cells of the light zone and outer zone in inducing centrocytes to differentiate to memory cells or plasmablasts are discussed.

Germinal center cells express bcl-2 protein after activation by signals which prevent their entry into apoptosis.

B cells undergo selection within germinal centers on the basis of their capacity to be activated by antigen held on follicular dendritic cells. Isolated germinal center B cells in culture kill themselves by apoptosis but this is prevented if their receptors for antigen are cross-linked. In this study it is confirmed that almost all germinal center B cells, unlike other B cells, do not express the 25-kDa protein encoded by the bcl-2 oncogene. Cross-linking the surface Ig of isolated germinal center cells causes them to express bcl-2 protein. Two other stimuli which inhibit the entry of germinal center cells to apoptosis result in the expression of bcl-2 protein. These stimuli are: (a) CD40 antibody and (b) recombinant 25-kDa fragment of the CD23 protein plus recombinant interleukin 1 alpha. Respectively, these induce germinal center cells to differentiate to resting B cells or plasmablasts. Dual-fluorescence studies on small lymphocytes confirm the presence of bcl-2 protein in mitochondria but show that this is also present in other extra-nuclear areas. Burkitt lymphoma cells have a phenotype which indicates that they are neoplastic cells of germinal center origin. The expression of bcl-2 protein by Burkitt lymphoma lines was also studied. Burkitt lines which retain the phenotype of fresh Burkitt lymphoma cells can be induced to enter apoptosis on culture with the Ca2+ ionophore ionomycin. These cells were found not to express bcl-2 protein. By contrast, Burkitt lines which have drifted towards a lymphoblastoid cell line phenotype and are resistant to the induction of apoptosis express high levels of the bcl-2 protein. The findings support the concept that the susceptibility of germinal center cells to entering apoptosis is associated with their lack of expression of bcl-2 protein. Aberrant expression of bcl-2 protein by some neoplastic germinal center cells may allow survival in situations where their normal counterparts die.

Use of monoclonal antibodies reactive with secretory epithelial cells for the immunocytochemical identification of plasma cells.

Six monoclonal antibodies (McAbs) were identified as plasma cell-reactive when screened on sections of human tonsil. They were all produced following immunisation of mice with cells of a human plasmacytoid line. Three of the antibodies also stained the cytoplasm (but not the surface) of blood B cells and were unreactive with other leucocytes; one McAb showed broad lymphocyte reactivity and two were completely unreactive with blood leucocytes; on testing with a panel of cell lines specificity for the plasmacytoid line was demonstrated by three of the McAbs. In spite of the marked restriction shown by the reactivity of these antibodies in tests on cells of haemopoietic origin, tests on other human tissues - including thyroid and pancreas - showed that a related antigen was present in the cytoplasm of secretory epithelial cells. The overall patterns of reactivity of the individual McAbs on various tissues and blood lymphocytes were different. Comparisons were made with the established McAb OKT10, which binds to plasma cells, early stem cells and activated lymphocytes; its binding to plasma cells was confirmed and it was shown that it did not stain secretory epithelia. The potent reactions obtained with the new McAbs suggest that antibodies to antigens associated with epithelial cell secretory apparatus provide potentially useful reagents for studying plasma cells.

Human follicular dendritic cells (FDC): a study with monoclonal antibodies (MoAb).

A collection of new and established FDC-reactive MoAb has been used in an immunohistological study designed to throw light on (a) the nature of FDC (which are of unknown lineage) as judged by their sharing of antigens with other cell types and (b) the reason for the strong expression of some B cell antigens on FDC. The MoAb were tested on: (1) sections of tonsil, (2) sections of lymph nodes from four cases of non-Hodgkin's lymphoma, (3) peripheral blood cells and (4) cells of cultured haemopoietic cell lines. Only one of the ten new MoAb bound to FDC and no other component of the tissues screened. It resembled R4/23, a MoAb known to be specific for FDC. The other nine antibodies showed a range of cross-reactivity patterns involving one or more of the following: monocytes, macrophages, platelets, epithelium, endothelium and connective tissue fibres. Some of the MoAb reacted with B lymphocytes and cells of B lymphoblastoid lines but none showed the restricted FDC-staining pattern associated with MoAb which detect the CD23, P45 antigen. The findings are discussed in terms of the intrinsic or extrinsic nature of the antigens detected.

Immunogenic and antigenic epitopes of immunoglobulins. II. Antigenic differences between secreted and membrane IgG demonstrated using monoclonal antibodies.

Twenty-three monoclonal antibodies with specificity for epitopes in the Fc fragment of IgG have been used to investigate antigenic differences between secreted and membrane forms of IgG produced by 2 human B lymphoblastoid cell lines (LCL). All of the monoclonals reacted with IgG secreted by the cell lines, as demonstrated by their ability to agglutinate SRBC coated with immunoglobulin isolated from culture supernatants. Membrane IgG expression was studied using direct and indirect rosette assays with antibody-coated ORBC. A surprisingly high number of antibodies, 13 on EB2 and 9 on EB4, did not bind to the cell surface immunoglobulin. These included antibodies with specificities for both C gamma 3 and C gamma 2 domain determinants. Similar results were obtained with an indirect radiobinding assay, indicating that negative results with the rosette test were not due to steric hindrance by the red cell carrier. Their performance in indirect hemagglutination indicated that most of the antibodies that did not bind to membrane IgG were of high avidity. It is concluded that the epitopes for which these antibodies are specific are not available on the cell surface. Possible explanations for the apparent antigenic differences between secreted and membrane forms of IgG are discussed against the background of previous work on the structure and mode of insertion of cell surface immunoglobulin.