Monoclonal antibodies against recombinant parts of the Ki-67 antigen (MIB 1 and MIB 3) detect proliferating cells in microwave-processed formalin-fixed paraffin sections

The monoclonal antibody Ki-67 reacts with a human nuclear cell proliferation-associated antigen that is expressed in all active parts of the cell cycle. Recently we have raised monoclonal antibodies, MIB 1-3, against recombinant parts of the Ki-67 antigen. These antibodies are true Ki-67 equivalents, as demonstrated by immunostaining of fresh specimens, biochemistry, and molecular biological techniques. Formalin-fixed, paraffin-embedded sections routinely processed for immunohistochemistry failed to stain for Ki-67 and MIB 2. Antibodies MIB 1 and MIB 3 labelled mitotic figures, while non-mitotic proliferating cells were negative under these conditions. However, when dewaxed microwave oven-processed paraffin sections of formalin-fixed tissues were used, MIB 1 and MIB 3 gave strong nuclear staining of those cells presumed to proliferate under a variety of normal and neoplastic conditions. Moreover, routine decalcification or depigmentation techniques did not alter the immunoreactivity of MIB 1 and MIB 3 with microwave-processed paraffin sections. This method is highly reproducible, easy to perform at low cost, and no additional technical skill is needed because after microwave treatment just routine immunohistochemical methods are used. Since we have successfully applied this new method to sections obtained from paraffin blocks stored for a long time (in one case more than 60 years), the assessment of cell kinetics through the detection of Ki-67 antigen is now possible on archival material collected in histopathology departments all over the world.

Gene expression profiling of B cell chronic lymphocytic leukemia reveals a homogeneous phenotype related to memory B cells

B cell-derived chronic lymphocytic leukemia (B-CLL) represents a common malignancy whose cell derivation and pathogenesis are unknown. Recent studies have shown that >50% of CLLs display hypermutated immunoglobulin variable region (IgV) sequences and a more favorable prognosis, suggesting that they may represent a distinct subset of CLLs which have transited through germinal centers (GCs), the physiologic site of IgV hypermutation. To further investigate the phenotype of CLLs, their cellular derivation and their relationship to normal B cells, we have analyzed their gene expression profiles using oligonucleotide-based DNA chip microarrays representative of approximately 12,000 genes. The results show that CLLs display a common and characteristic gene expression profile that is largely independent of their IgV genotype. Nevertheless, a restricted number of genes (<30) have been identified whose differential expression can distinguish IgV mutated versus unmutated cases and identify them in independent panels of cases. Comparison of CLL profiles with those of purified normal B cell subpopulations indicates that the common CLL profile is more related to memory B cells than to those derived from naive B cells, CD5(+) B cells, and GC centroblasts and centrocytes. Finally, this analysis has identified a subset of genes specifically expressed by CLL cells of potential pathogenetic and clinical relevance.

The BCL-6 proto-oncogene controls germinal-centre formation and Th2-type inflammation

Structural alterations of the promoter region of the BCL-6 proto-oncogene represent the most frequent genetic alteration associated with non-Hodgkin lymphoma, a malignancy often deriving from germinal-centre B cells. The BCL-6 gene encodes a zinc-finger transcriptional repressor normally expressed in both B cells and CD4+ T cells within germinal centres, but its precise function is unknown. We show that mice deficient in BCL-6 displayed normal B-cell, T-cell and lymphoid-organ development but have a selective defect in T-cell-dependent antibody responses. This defect included a complete lack of affinity maturation and was due to the inability of follicular B cells to proliferate and form germinal centres. In addition, BCL-6-deficient mice developed an inflammatory response in multiple organs characterized by infiltrations of eosinophils and IgE-bearing B lymphocytes typical of a Th2-mediated hyperimmune response. Thus, BCL-6 functions as a transcriptional switch that controls germinal centre formation and may also modulate specific T-cell-mediated responses. Altered expression of BCL-6 in lymphoma represents a deregulation of the pathway normally leading to B cell proliferation and germinal centre formation.

Antigen unmasking on formalin-fixed, paraffin-embedded tissue sections

Enzymatic and non-enzymatic treatments for antigen unmasking on formalin-fixed, paraffin-embedded, dewaxed sections were optimized and compared by the use of a panel of antibodies of diagnostic relevance (anti-cytokeratins, vimentin, S-100, T- and B-cell receptors, Ki-67/MIB 1, muscle actin). Non-enzymatic unmasking was obtained by boiling the slides in a microwave oven in 0.01 M salt solution (pH 6) or in 6 M urea. Trypsin or pronase digestion was used for comparison and found to be necessary for some of the reagents. The investigation was then extended to 256 antibodies; the epitopic amino acid sequence was known for 48 of them. We found that enzymatic and non-enzymatic antigen unmasking are not dependent on the epitope sequence, but some antigens benefit selectively from one treatment but not from the other. Denaturation of proteins is the likely mechanism which leads to immunodetection on microwave oven-boiled slides; this suggestion is supported by the use of denaturating solutions and by the observation that endogenous enzymes were inactivated and a few antigens were no longer immunodetectable after boiling. Non-enzymatic methods for antigen unmasking are a powerful new tool for broadening the use of antibodies for immunostaining formalin-fixed, paraffin-embedded sections and should be used in parallel with the traditional enzymatic methods.

Meiotic pachytene arrest in MLH1-deficient mice

Germ line mutations in DNA mismatch repair genes including MLH1 cause hereditary nonpolyposis colon cancer. To understand the role of MLH1 in normal growth and development, we generated mice that have a null mutation of this gene. Mice homozygous for this mutation show a replication error phenotype, and extracts of these cells are deficient in mismatch repair activity. Homozygous mutant males show normal mating behavior but have no detectable mature sperm. Examination of meiosis in these males reveals that the cells enter meiotic prophase and arrest at pachytene. Homozygous mutant females have normal estrous cycles and reproductive and mating behavior but are infertile. The phenotypes of the mlh1 mutant mice are distinct from those deficient in msh2 and pms2. The different phenotypes of the three types of mutant mice suggest that these three genes may have independent functions in mammalian meiosis.

P53 expression in breast cancer

Immunohistochemical evaluation of 200 primary breast cancers with the anti-p53 mouse monoclonal antibody (MAb) PAb421 showed positivity in nuclei of malignant cells in 31 cases (15.5%). PAb421+ cases were significantly more frequently epidermal growth factor receptor (EGF-R)-positive (67.7%; p less than 0.001) and estrogen receptor (ER)-negative (73.3%; p less than 0.001); they displayed surface histocompatibility class-1 (80.6%; p less than 0.01) and 11 (74.2%; p less than 0.05) antigens. Low values for progesterone receptor (mean 67.20 +/- 25.2 fmol/mg; p less than 0.05) and a high number of cells positive for the proliferation-associated antigen Ki-67 (log mean 6.88 +/- 0.33; p less than 0.01) were found in PAb421+ tumors as well as a high number of grade-3 infiltrating duct carcinomas (70%; p = 0.01). Of the 200 cases of mammary carcinoma, 88 were further analyzed using another human specific anti-p53 MAb PAb1801, and 40 (45.5%) were found positive. This MAb stained all the PAb421+ cases and was significantly associated with negative ER status (39.5%; p less than 0.05) and high Ki-67 scores (log mean 6.93 +/- 0.24; p = 0.001). Analysis of PAb1801+/Pab421- cases for HLA antigens, EGF-R and ER showed a phenotype similar to that of the p53-ve/ER+ carcinomas, except for the high Ki-67 score. No differences in age of the patient, number of involved nodes, tumor size, ploidy or labelling index scores were evident between p53+ and carcinomas. We concluded that p53 in mammary carcinomas is associated with ER-negative, growth factor receptor-positive, high-grade tumors, and is a promising new parameter to evaluate the cellular biology and prognosis of breast cancer.

Acute leukemia with promyelocytic features in PML/RARalpha transgenic mice

Acute promyelocytic leukemia (APL) is associated with reciprocal chromosomal translocations involving the retinoic acid receptor alpha (RARalpha) locus on chromosome 17. In the majority of cases, RARalpha translocates and fuses with the promyelocytic leukemia (PML) gene located on chromosome 15. The resulting fusion genes encode the two structurally unique PML/RARalpha and RARalpha/PML fusion proteins as well as aberrant PML gene products, the respective pathogenetic roles of which have not been elucidated. We have generated transgenic mice in which the PML/RARalpha fusion protein is specifically expressed in the myeloid-promyelocytic lineage. During their first year of life, all the PML/RARalpha transgenic mice have an abnormal hematopoiesis that can best be described as a myeloproliferative disorder. Between 12 and 14 months of age, 10% of them develop a form of acute leukemia with a differentiation block at the promyelocytic stage that closely mimics human APL even in its response to retinoic acid. Our results are conclusive in vivo evidence that PML/RARalpha plays a crucial role in the pathogenesis of APL.

Commitment of B lymphocytes to a plasma cell fate is associated with Blimp-1 expression in vivo

B lymphocyte-induced maturation protein-1 (Blimp-1) is a transcriptional repressor that is sufficient to trigger terminal differentiation in the B cell lymphoma BCL-1. In this study, we have determined the expression pattern of Blimp-1 in vivo in primary and secondary lymphoid organs of humans and immunized mice. Blimp-1 is expressed in plasma cells derived from either a T-independent or T-dependent response in plasma cells that have undergone isotype switching and those resulting from secondary immunization. Blimp-1 is also present in long-lived plasma cells residing in the bone marrow. However, Blimp-1 was not detected in memory B cells. This expression pattern provides further evidence of a critical role for Blimp-1 in plasma cell development, supporting earlier studies in cultured lines. Significantly, Blimp-1 was also found in a fraction (4-15%) of germinal center B cells in murine spleen and human tonsils. Blimp-1 expression in the germinal center is associated with an interesting subset of cells with a phenotype intermediate between germinal center B cells and plasma cells. In the mouse, Blimp-1(+) germinal center B cells peak at day 12 postimmunization and disappear soon thereafter. They are not apoptotic, some are proliferating, they express germinal center markers peanut agglutinin or CD10 but not Bcl-6, and most express CD138 (syndecan-1), IRF4, and cytoplasmic Ig. Together, these data support a model in which B cell fate decisions occur within the germinal center and Blimp-1 expression is critical for commitment to a plasma cell, rather than a memory cell, fate.

Selective growth response to IL-3 of a human leukaemic cell line with megakaryoblastic features

A new human leukaemic cell line (M-O7) with the phenotypic characteristics of CFU-mega is described. Its cells are positive for T200 leucocyte common antigen (LCA) and negative with MAbs recognizing T and B cells and mature myelomonocytic antigens. In contrast, they react with MAbs recognizing antigenic determinants common to multi-lineage (CD13, CD33, CD34) and to bipotent erythromegakaryoblastic (CD36, H25) haemopoietic precursors, and with MAbs specific for platelet glycoproteins (CD41w, CD42w). A small proportion (10%) of the cells were large and multinucleated, and on electron-microscopy examination showed peripheral splitting of platelet-like cytoplasm particles. When transferred to a serum-free Iscove modified Dulbecco's medium supplemented with human insulin and transferrin, M-O7 cells stop proliferating. Of the haemopoietic growth factors tested for their ability to restore the proliferative activity of this quiescent population, only rH IL-3 proved effective. Moreover, it also increased the cloning efficiency in methylcellulose more than any other CSFs. The M-O7 cell line may provide a valuable tool for the biological assay of IL-3, and a model for biochemical studies of the megakaryocytic lineage.

Transcriptional repression of Stat6-dependent interleukin-4-induced genes by BCL-6: specific regulation of iepsilon transcription and immunoglobulin E switching

The BCL-6 proto-oncogene encodes a POZ/zinc-finger transcription factor that is expressed in B cells and a subset of CD4(+) T cells within germinal centers. Recent evidence suggests that BCL-6 can act as a sequence-specific repressor of transcription, but the target genes for this activity have not yet been identified. The binding site for BCL-6 shares striking homology to the sites that are the target sequence for the interleukin-4 (IL-4)-induced Stat6 (signal transducers and activators of transcription) signaling molecule. Electrophoretic mobility shift assays demonstrate that BCL-6 can bind, with different affinities, to several DNA elements recognized by Stat6. Expression of BCL-6 can repress the IL-4-dependent induction of immunoglobulin (Ig) germ line epsilon transcripts, but does not repress the IL-4 induction of CD23 transcripts. Consistent with the role of BCL-6 in modulating transcription from the germ line epsilon promoter, BCL-6(-/-) mice display an increased ability to class switch to IgE in response to IL-4 in vitro. These animals also exhibit a multiorgan inflammatory disease characterized by the presence of a large number of IgE(+) B cells. The apparent dysregulation of IgE production is abolished in BCL-6(-/-) Stat6(-/-) mice, indicating that BCL-6 regulation of Ig class switching is dependent upon Stat6 signaling. Thus, BCL-6 can modulate the transcription of selective Stat6-dependent IL-4 responses, including IgE class switching in B cells.

IRTA1 and IRTA2, novel immunoglobulin superfamily receptors expressed in B cells and involved in chromosome 1q21 abnormalities in B cell malignancy

Abnormalities of chromosome 1q21 are common in B cell malignancies, but their target genes are largely unknown. By cloning the breakpoints of a (1;14) (q21;q32) chromosomal translocation in a myeloma cell line, we have identified two novel genes, IRTA1 and IRTA2, encoding cell surface receptors homologous to the Fc and inhibitory receptor families. Both genes are selectively expressed in mature B cells: IRTA1 in marginal zone B cells and IRTA2 in centrocytes, marginal zone B cells, and immunoblasts. As a result of the t(1;14), IRTA1 is fused to the immunoglobulin Calpha domain to produce a chimeric IRTA1/Calpha fusion protein. In tumor cell lines with 1q21 abnormalities, IRTA2 expression is deregulated. Thus, IRTA1 and IRTA2 are novel immunoreceptors implicated in B cell development and lymphomagenesis.

BCL-6 regulates chemokine gene transcription in macrophages

The transcriptional repressor protein BCL-6, implicated in the pathogenesis of B cell lymphoma, regulates lymphocyte differentiation and inflammation. We investigated the mechanism for the T helper cell subset 2 (TH2)-type inflammation that occurs in BCL-6-/- mice. Using chimeric mice we found that the TH2-type inflammation is dependent upon nonlymphoid cells. We identified three chemokines, MCP-1, MCP-3 and MRP-1, which are negatively regulated by BCL-6 in macrophages. Promoter analysis revealed that BCL-6 is a potent repressor of MCP-1 transcription. Our results provide a mechanism for the regulation of TH2-type inflammation by BCL-6 and link TH2 differentiation to innate immunity.

Mzf1 controls cell proliferation and tumorigenesis

MZF1 is a transcription factor belonging to the Krüppel family of zinc finger proteins, expressed in totipotent hemopoietic cells as well as in myeloid progenitors. Here we have inactivated Mzfi1 by gene targeting. Mzf1(-/-) mice develop lethal neoplasias characterized by the infiltration and complete disruption of the liver architecture by a monomorphic population of cells of myeloid origin reminiscent of human chloromas. Mzf1 inactivation results in a striking increase of the autonomous cell proliferation and of the ability of Mzf1(-/-) hemopoietic progenitors to sustain long-term hemopoiesis. These findings demonstrate that Mzf1 can act as a tumor/growth suppressor in the hemopoietic compartment.

Bcl-2 protein expression in carcinomas originating from the follicular epithelium of the thyroid gland

The bcl-2 product has been related to the block of programmed cell death (apoptosis) both in lymphoid and in epithelial cells. The pathological expression of bcl-2 has been investigated mainly in haematological malignancies. Here we have investigated bcl-2 expression in a model of epithelial tumours represented by the spectrum of carcinomas arising from the follicular epithelium of the human thyroid gland. The analysis was carried out by immunocytochemistry on archival material using monoclonal antibodies against bcl-2 and thyroglobulin (Tg) on consecutive sections of 94 well-differentiated carcinomas (WDCs), 19 poorly differentiated carcinomas (PDCs), and 22 undifferentiated carcinomas (UCs) of the thyroid gland. In a subset of 5 cases of UC showing a differentiated component (UC-D), the expression of p53 protein was also investigated. As controls, fetal and adult normal thyroid glands and adenomas were analysed. bcl-2 expression was detected in 74 of 94 cases (78.7 per cent) of WDC, 16 of 19 cases (84.2 per cent) of PDC, and 3 of 22 cases (13.6 per cent) of UC. Simultaneous expression of bcl-2 protein and Tg was observed in 74 of 94 cases (78.7 per cent) of WDC, 13 of 19 cases (68.4 per cent) of PDC, and in no case of UC. bcl-2 and Tg immunostaining was detected in all fetal and normal thyroid glands as well as in the adenoma specimens examined. In the subset of UC-D, mutual exclusion of bcl-2 and p53 expression was observed in the undifferentiated and differentiated components (p53 but not bcl-2 expressed in the former).(ABSTRACT TRUNCATED AT 250 WORDS)

Vimentin and p53 expression on epidermal growth factor receptor-positive, oestrogen receptor-negative breast carcinomas

The coordinate expression of the nuclear p53 protein, cytoplasmic intermediate filament vimentin (VIM) and membrane epidermal growth factor receptor (EGF-R) was significantly associated with oestrogen receptor immunocytochemical nuclear stain (ER-ICA) negative breast carcinomas. Twenty-three (51.1%), 26 (57.8%) and 27 (60%) of 45 ER-ICA -ve cancers were respectively p53 +ve, VIM +ve and EGF-R +ve; whereas of 151 ER-ICA +ve tumours 8 (5.3%) were p53 +ve (P less than 0.0001), 23 (15.2%) VIM +ve (P less than 0.001) and 40 (26.5%) EGF-R +ve P less than 0.001). Thirty-six of 45 (80%) ER-ICA -ve carcinomas were positive for at least one of the markers versus 55/151 (36.4%) ER-ICA +ve cases (chi 2 = 28.92, P less than 0.001). A prevalence of high grade carcinomas was found among p53 +ve, VIM +ve cases; the latter subset of tumours also had a larger mean diameter. These results suggest that ER -ve breast carcinoma cells display a coordinate expression of cell cycle-related proteins and marked changes of both the cytoskeleton and the membrane receptor repertoire.

Postmortem microcomputed tomography (micro-CT) of small fetuses and hearts

OBJECTIVE

To assess the feasibility and utility of contrast-enhanced microcomputed tomography (micro-CT) for identifying structural anomalies in ex-vivo first- and second-trimester human fetuses and isolated fetal hearts.

METHODS

Radiopaque iodine staining and micro-CT scanning protocols were first developed in rodent studies and then used to examine routinely fixed whole human fetuses (n = 7, weight 0.1-90 g, gestational age, 7-17 weeks) and isolated fetal hearts (n = 14, weight 0.1-5.2 g, gestational age, 11-22 weeks). Samples were scanned using an isotropic resolution of 18 (and, if necessary, 9 or 35) µm and findings were interpreted jointly by four fetal pathologists, a fetal cardiologist and a radiologist. Samples with gestational ages ≥ 13 weeks also underwent conventional autopsy or dissection.

RESULTS

Micro-CT identified all anatomical structures and abnormalities documented by the macroscopic examination. In all seven cases involving fetuses ≤ 13 weeks (four fetuses, three isolated hearts), micro-CT excluded the presence of structural anomalies. In the remaining 14 cases, it provided all the information obtained with invasive autopsy or dissection and in seven of the 14 (two fetuses, five isolated hearts) it furnished additional diagnostic details.

CONCLUSIONS

This pilot study confirms the feasibility of postmortem contrast-enhanced micro-CT assessment of structural anomalies in whole small fetuses and fetal hearts. Further study is needed to confirm our findings, particularly in whole fetuses, and to define the extent to which this virtual examination might be used instead of conventional invasive autopsy.

Leukemia with distinct phenotypes in transgenic mice expressing PML/RAR alpha, PLZF/RAR alpha or NPM/RAR alpha

Recurrent chromosomal translocations involving the RAR alpha locus on chromosome 17 are the hallmark of acute promyelocytic leukemia (APL). The RAR alpha gene fuses to variable partners (PML, PLZF, NPM, NuMA and STAT5B: X genes) leading to the expression of APL-specific fusion proteins with identical RAR alpha moieties. To analyse whether the variable X moiety could affect the activity of the fusion protein in vivo, we generated and characterized, on a comparative basis, NPM/RAR alpha transgenic mice (TM) in which the fusion gene is expressed under the control of a human Cathepsin G (hCG) minigene. We compared the features of the leukemia observed in these TM with those in hCG-PML/RAR alpha and hCG-PLZF/RAR alpha TM. In all three transgenic models, leukemia developed after a variably long latency, with variable penetrance. However, the three leukemias displayed distinct cytomorphological features. hCG-NPM/RAR alpha leukemic cells resembled monoblasts. This phenotype contrasts with what was observed in the hCG-PML/RAR alpha TM model in which the leukemic phase was characterized by the proliferation of promyelocytic blasts. Similarly, hCG-PLZF/RAR alpha TM displayed a different phenotype where terminally differentiated myeloid cells predominated. Importantly, the NPM/RAR alpha oncoprotein was found to localize in the nucleolus, unlike PML/RAR alpha and PLZF/RAR alpha, thus possibly interfering with the normal function of NPM. Similarly to what was observed in human APL patients, we found that NPM/RAR alpha and PML/RAR alpha, but not PLZF/RAR alpha leukemia, was responsive to all-trans retinoic acid (ATRA) or As2O3 treatments. Taken together, our results underscore the critical relevance of the X moiety in dictating the biology of the disease and the activity of the APL fusion oncoprotein.

A novel panel of antibodies that segregates immunocytochemically poorly differentiated carcinoma from undifferentiated carcinoma of the thyroid gland

The expression of bcl-2 and p53 was investigated by immunocytochemistry in combination with that of conventional structural and differentiation antigens on the archival material of 22 cases of undifferentiated carcinoma (UC) and 19 of poorly differentiated carcinoma (PDC) of the thyroid gland. The restriction of bcl-2 expression to PDC in comparison to UC was 84.2% versus 13.6% of cases, respectively, in contrast to an almost equal percentage of p53 expression in the two histologic types, that is, 52.6% and 54.5% of cases of PDC and UC, respectively. However, the pattern of distribution of p53-immunoreactive cells was definitely different, being restricted to areas showing active infiltrating growth in PDC and involving almost all tumor cells in UC. Furthermore, in the subset of cases of UC showing the residual presence of a differentiated component, a distinctive mutual exclusion of bcl-2 and p53 immunoreactivity was observed in the two components. The results suggest that the evaluation of bcl-2 expression may be usefully applied to the differentiation of PDC from UC, whereas all morphologic findings related to p53 expression are in keeping with a significant role of the deregulation of this gene in the mechanism of dedifferentiation and progression of the disease.

Interferon gamma signaling alters the function of T helper type 1 cells

One mechanism regulating the ability of different subsets of T helper (Th) cells to respond to cytokines is the differential expression of cytokine receptors. For example, Th2 cells express both chains of the interferon gamma receptor (IFN-gammaR), whereas Th1 cells do not express the second chain of the IFN-gammaR (IFN-gammaR2) and are therefore unresponsive to IFN-gamma. To determine whether the regulation of IFN-gammaR2 expression, and therefore IFN-gamma responsiveness, is important for the differentiation of naive CD4(+) T cells into Th1 cells or for Th1 effector function, we generated mice in which transgenic (TG) expression of IFN-gammaR2 is controlled by the CD2 promoter and enhancer. CD4(+) T cells from IFN-gammaR2 TG mice exhibit impaired Th1 polarization potential in vitro. TG mice also display several defects in Th1-dependent immunity in vivo, including attenuated delayed-type hypersensitivity responses and decreased antigen-specific IFN-gamma production. In addition, TG mice mount impaired Th1 responses against Leishmania major, as manifested by increased parasitemia and more severe lesions than their wild-type littermates. Together, these data suggest that the sustained expression of IFN-gammaR2 inhibits Th1 differentiation and function. Therefore, the acquisition of an IFN-gamma-unresponsive phenotype in Th1 cells plays a crucial role in the development and function of these cells.

Cellular, intracellular, and developmental expression patterns of murine SWAP-70

SWAP-70 is part of a protein complex that catalyzes cell-free DNA recombination between immunoglobulin heavy chain gene switch region substrates. This report studies the expression pattern of SWAP-70 in mouse tissues, sorted cells, and cultured primary cells. SWAP-70 RNA is strongly increased upon switch-induction of spleen cells, and very weakly expressed in thymus and bone marrow. SWAP-70 protein is specifically expressed in B cells, and levels increase rapidly after stimulation. Tissue staining shows strong expression in germinal center B cells, while macrophages and T lymphocytes do not stain. SWAP-70 is not detected in early B cells in the bone marrow. Its expression during mouse ontogeny after birth correlates with the appearance of non-IgM isotypes. While SWAP-70 localizes to the cell nucleus in activated B cells, it is not tightly associated with the chromatin and is found in the cytoplasm as well. SWAP-70 expression is not increased by gamma or UV irradiation of spleen cells, nor does it depend on p53. These characteristics are consistent with the putative role of SWAP-70 in immunoglobulin class switching.

The high lysability by LAK cells of colon-carcinoma cells resistant to doxorubicin is associated with a high expression of ICAM-1, LFA-3, NCA and a less-differentiated phenotype

A human colon-carcinoma cell subline resistant to doxorubicin (LoVo/Dx), previously shown to be more lysed than the chemosensitive subline LoVo/H by different immune effectors, is reported here to be similarly susceptible to direct, anti-proliferative effect of soluble cytokines (TNF-alpha and/or IFN-gamma). More adhesion molecules ICAM-1, LFA-3 and NCA were expressed on LoVo/Dx than on LoVo/H, while no significant amounts of CEA were detectable on the cell surface or in culture supernatant of either tumor subline. Anti-ICAM-1, anti-LFA-3 and anti-NCA monoclonal antibodies (MAbs) caused a marked reduction of lysis by interleukin-2 (IL-2) activated lymphocytes (LAK) of LoVo/Dx, whereas a lower effect was evident on LoVo/H. A pool of these antibodies was able to further increase the inhibition of the LAK lysis of both sublines. LoVo/Dx displayed a less differentiated phenotype as assessed by morphology, in vitro growth and altered or increased expression of markers such as desmoplakin and vimentin respectively, and disappearance of mucin. Treatment of LoVo sublines with differentiating agents (dimethylformamide and retinoic acid) led to a decreased expression of all adhesion molecules studied, accompanied by increased resistance to LAK-mediated lysis. These data indicate that sensitivity of chemoresistant tumor cells to cytotoxic effectors depends on the level of expression of adhesion molecules, including NCA, and is related to differentiation stage.

Improved avidin-biotin-peroxidase complex (ABC) staining

A considerable intensification of the avidin-biotin-peroxidase complex staining system (ABC) was obtained by sequentially overlaying the sections to be immunostained with an avidin-rich and a biotin-rich complex. Each sequential addition contributed to the deposition of horseradish peroxidase on the immunostained site and allowed the subsequent binding of a complementary complex. With this technique a higher dilution of the antisera could be used and minute amounts of antigen masked by the fixative could be demonstrated on paraffin sections.

Immuno-electron microscopy characterization of human bone marrow stromal cells with anti-NGFR antibodies

Human bone marrow stromal cells have been examined with an immuno-electron microscopy technique in order to better define their structure and function in normal hematopoiesis. Bone marrow fragments from normal donors, after mild permeabilization and glutaraldehyde prefixation were labeled with the Me20.4 Mab, which recognizes the low affinity nerve growth factor (NGFR) and was recently described as specifically identifying fibroblastic-like bone marrow stromal cells. Five nm gold immuno-conjugates served as markers. NGFR+ cells were showing either a star-shape, with long and convoluted dendritic projections, and branching with each other to form a complex system of lacunae upon which hematopoietic cells were arranged. Other NGFR+ cells had an elongated spindle-like morphology. NGFR+ dendrites were seen in close contact with each other and with the different hematopoietic cells, although definite junctions were never noticed. NGFR+ dendrites were also observed surrounding mature plasma cells, in close apposition with adipocytes or surrounding bone marrow sinusoids. These findings may give some clues about the function of the bone marrow stromal cells, which are known to be involved in the homing and recirculation of hemopoietic cells; in addition, the presence and distribution of NGFR in the bone marrow stroma may support the recent evidence of a co-stimulatory effect of NGF in early hematopoiesis.