Cytokeratin 14 expression in rat liver cells in culture and localization in vivo

Rat liver epithelial cells (LECs) are non-parenchymal proliferating cells that readily emerge in primary culture and can be established as cell lines, but their in vivo cell(s) of origin is unclear. We reported recently some evidence indicating that the LEC line, T51B, contains two cytokeratins (CKs) equivalent to human CK8 and CK14 respectively. T51B cells also contain vimentin assembled as a network of intermediate filaments distinct from that of the CKs. In the present study, we examined the expression of CK14 gene in various LEC preparations and a Triton-resistant rat skin cytoskeletal fraction, and then assessed its usefulness as an LEC specific marker in the liver. Northern and Western blot analyses with cDNAs and antibodies for CK8, CK14, CK18 and vimentin confirmed that rat hepatocytes express CK8 and CK18 genes only, whereas T51B cells express CK8, CK14 and vimentin genes in the absence of CK18. CK14 was also present in LECs derived as primary from embryonic-day 12 rat liver and secondary cultures from 4-day-old rat liver. Primary cultures of oval cells isolated from 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) treated rat liver (an enriched source of biliary epithelial cells) contained CK14 mRNAs which were slightly shorter than those in LECs. The analyses of CK5 (the usual partner of CK14) gene expression using specific cDNA and antibody clearly demonstrated its absence in LECs. In situ double immunolocalization analyses by laser scanning confocal microscopy showed that CK14 was not present in hepatocytes (HES6+ cells) and was expressed in some biliary epithelial (BDS7+ cells). CK14-positive cells were also found in the Glisson's capsule. However, CK14-positive cells of the portal region were vimentin negative, whereas those of the Glisson's capsule were vimentin positive. Our results suggest that CK14 gene expression is part of the differentiation program of two types of LECs and that this differential CK14 gene expression can be used as a new means to type LECs in culture and in vivo.     

Expression of surface lymphotoxin and tumor necrosis factor on activated T, B, and natural killer cells.

The expression of membrane-associated forms of lymphotoxin (LT) and TNF were examined on cell lines of T, B, and myeloid origin, IL-2 dependent T cell clones, and peripheral blood lymphocytes. Inducible and constitutive patterns of surface LT expression were found on T cells as exemplified by the II-23.D7, a CD4+T cell hybridoma, and HUT-78, a T cell lymphoma. Phorbol ester induced surface LT expression on Ramos, an EBV transformed B cell line, but at a slower rate of appearance when compared to the II-23.D7. Secretion of LT was rapidly inducible by phorbol ester in II-23.D7 and also in HUT-78 but with slower kinetics; surface LT expression continued in both lines after secretion had ceased. Low levels of membrane TNF were transiently induced on II-23.D7 and HUT-78, but none was observed on Ramos. Peripheral blood monocytes and some myeloid tumor lines did not express surface LT. Several T cell clones expressed surface LT after Ag-specific stimulation, and expression persisted several days. Stimulation through the TCR or by IL-2 rapidly induced surface LT on resting peripheral T cells and CD56+ NK cells; pokeweed mitogen activation induced expression on CD20+ B cells. Consistent with previous results, immunoprecipitation with anti-LT mAb showed that LT was complexed with a distinct 33 kDa glycoprotein (p33) on cells that expressed surface LT, whereas secreted LT was not associated with p33. Surface and secreted modes of LT expression by activated T, B, and NK cells suggests that LT can be utilized as either a localized or diffusible mediator in immune responses.     

Connections of intermediate filaments with the nuclear lamina and the cell periphery

We investigated the relationship between intermediate filaments (IFs) and other detergent- and nuclease-resistant filamentous structures of cultured liver epithelial cells (T51B cell line) using whole mount unembedded preparations which were sequentially extracted with Triton X-100 and nucleases. Immunogold labelling and stereoscopic observation facilitated the examination of each filamentous structure and their three-dimensional relationships to each other. After solubilizing phospholipid, nucleic acid and soluble cellular protein, the resulting cytoskeleton preparation consisted of a network of cytokeratin and vimentin IFs linked by 3 nm filaments. The IFs were anchored to and determined the position of the nuclear lamina filaments (NLF) network and the centrioles. The NLF was composed of the nuclear lamina filaments measuring 3-6 nm in diameter which radiated from and anchored to the skeleton of the nuclear pores. The IFs located in the nuclear region appeared to be interwoven with the NLF. At the cell surface, the IFs seemed to be attached to the putative actin filament network. They formed a focally interrupted plexus-like structure at the cell periphery. Fragments of vimentin filaments were found among the filamentous network located at the cell surface, and some filaments terminated blindly there.     

Intermediate filament expression and lifespan potential in human somatic cell hybrids

Summary Limited lifespan human diploid fibroblast cells have been fused with the HeLa derived cell line HEB 7A which possesses transformed growth characteristics and unlimited division potential. HEB 7A expresses keratin intermediate filaments, while the fibroblast cells express only vimentin intermediate filaments. Independently arising clones of hybrids were examined for the presence of keratin by indirect immunofluorescence. Of 11 limited lifespan hybrids, all were keratin negative and possessed the growth characteristics of the fibroblast parent. Of 8 transformed hybrids, 6 arising early after fusion and 2 arising late, all were keratin-positive and simultaneously expressed the transformed growth characteristics of loss of density dependent growth inhibition, low serum dependence, and anchorage independence. It is concluded that the growth properties of these hybrids are associated with the type of intermediate filament expressed. The intermediate filament expression is therefore a marker of proliferative potential in these hybrids. This work was supported by grant no. AG 02664 from NIA (to C.L.B.) and by grant nos. 1R01 HD 18129-01 from NIH and PCM83-09068 from NSF (to R.H.S.). Editor’s Statement The tight correlation between the expression of the intermediate filaments of the immortal parent in hybrids of limited lifespan fibroblasts and HeLa cells with the transformed phenotype is of interest. It may offer important clues to the mechanism involved in cellular senescence. Gordon H. Sato     

Interaction of cblA/adhesin-positive Burkholderia cepacia with squamous epithelium

A highly transmissible strain of Burkholderia cepacia from genomovar III carries the cable pilin gene, expresses the 22 kDa adhesin (cblA +ve/Adh +ve), binds to cytokeratin 13 (CK13) and is invasive. CK13 is expressed abundantly in the airway epithelia of cystic fibrosis (CF) patients. We have now investigated whether binding of cblA +ve/Adh +ve B. cepacia to CK13 potentiates bacterial invasion and epithelial damage using bronchial epithelial cell cultures differentiated into either squamous (CK13-enriched) or mucociliary (CK13-deficient) epithelia. Three different B. cepacia isolates (cblA +ve/Adh +ve, cblA +ve/Adh -ve and cblA -ve/Adh -ve) showed minimal binding to mucociliary cultures, and did not invade or cause cell damage. In contrast, the cblA +ve/Adh +ve isolate, but not others, bound to CK13-expressing cells in squamous cultures, caused cytotoxicity and stimulated IL-8 release within 2 h. By 24 h, this isolate invaded and migrated across the squamous culture, causing moderate to severe epithelial damage. A specific antiadhesin antibody, which blocked the initial binding of the cblA +ve/Adh +ve isolate to CK13, significantly inhibited all the pathologic effects. Transmission electron microscopy of squamous cultures incubated with the cblA +ve/Adh +ve isolate, revealed bacteria on the surface surrounded by filopodia by 2 h, and within the cells in membrane-bound vesicles by 24 h. Bacteria were also observed free in the cytoplasm, surrounded by intermediate filaments containing CK13. These findings suggest that binding of B. cepacia to CK13 is an important initial event and that it promotes bacterial invasion and epithelial damage.     

Analysis of cellular immune response to EBV by using cloned T cell lines

Eight cloned T cell lines specific for Epstein Barr virus-transformed B lymphocytes were derived. In the presence of the autologous virus-infected B cells, the T cell lines show HLA-restricted cytotoxic activity and also secrete alpha-interferon in sufficient amounts to inhibit infection and transformation. Four of these clones showed restriction to a single HLA locus (two for A3, and two for B7) and three showed exquisite self-restriction lysing only autologous targets. These seven clones expressed the classical cell surface phenotype of cytotoxic T cells being T3, 8, 11, and la-positive and T4-negative. An eighth clone that lacked the T8 surface marker appeared to recognize both B7 and BW51. HLA restriction was confirmed: 1) by the ability of a monoclonal antibody against an HLA-A,B,C framework antigen (W6-32) to block the cytotoxicity; 2) the failure of the clones to lyse Daudi, an EBV-positive, HLA-A,B, C-negative cell line; and 3) successful competition of the cytotoxicity by autologous but not allogeneic cold targets. The cloned T cells do not kill EBV-negative targets such as autologous pokeweed mitogen blasts and cell lines including CEM and the natural killer cell target K562. The results suggest T cell clones may be generated against an EBV-associated membrane antigen on transformed B cells, perhaps equivalent to the lymphocyte-determined membrane antigen, and that the recognition is restricted by a single HLA determinant. We propose that single T cells can play multiple roles in controlling EBV infection in vitro and in vivo including the elimination of transformed cells by cytotoxicity and the prevention by secreted interferon of further re-infection and transformation.     

Phosphorylation of cytokeratin 17 by herpes simplex virus type 2 US3 protein kinase

We previously reported the establishment of an HEp2 cell line which expresses the US3 protein kinase (PK) of herpes simplex virus type 2 (HSV-2) upon induction with IPTG. Here we report that expression, phosphorylation and ubiquitination of cytokeratin 17 (CK17) are enhanced in US3-expressing HEp2 cells. In vitro kinase and co-immunoprecipitation assays provided evidence that US3 PK directly phosphorylates CK17. Expression of US3 PK caused a significant decrease in filamentous staining of CK17, suggesting that phosphorylation of CK17 by US3 PK causes a disruption of intermediate filaments. Our observations suggest a role for US3 in the regulation of CKs and intermediate filaments in cells. Moreover, we found that infection of a keratinocyte-derived cell line, A431, with a US3-deficient virus, results in cytopathic effects that are morphologically distinct from those induced by wild-type and revertant viruses, suggesting that US3 PK may be important for interaction between HSV-2 and peripheral epithelial cells.     

Ca2+-dependent cell surface protein phosphorylation may be involved in the initiation of DNA synthesis

Incubating T51B rat liver cells in Ca2+-deficient, serum-rich medium containing only 0.02 mM Ca2+ strikingly decreased the phosphorylation of several trypsin-removable cell surface proteins and arrested the cells in late G1 phase. Raising the Ca2+ concentration in the Ca2+-deficient medium from 0.02 mM to 0.5 mM or adding 80 nM TPA (12-O-tetradecanoyl-phorbol-13-acetate), a protein kinase C activator, stimulated the phosphorylation of a certain set of surface proteins within 5 min and the initiation of DNA replication within the next 2 hr. By contrast, incubation in the same Ca2+-deficient medium, which does not affect the proliferation of neoplastic T51B-261B cells, did not reduce the phosphorylation of cell surface proteins. These observations suggest that the stimulation of a Ca2+-dependent protein kinase (possibly protein kinase C) directly or indirectly phosphorylates certain cell surface proteins that might be part of the mechanism that triggers the Ca2+-dependent G1----S transition of normal cells. They also suggest that an alteration of this Ca2+-dependent protein kinase might be the reason for neoplastic cells being able to proliferate in the face of an external Ca2+ shortage that would stop the proliferation of normal cells.     

Cytoplasmic suppression of malignancy

Summary Using both normal and transformed rat liver epithelial cells to prepare cytoplasmic hybrids (cybrids) we have found evidence to support the theory that the cytoplasm from a normal cell can suppress tumorigenicity. A unique aspect of this study is that all of the cells utilized, both normal and malignantly transformed, were derived from an original cloned cell. We found that fusing cytoplasts from normal cells to malignantly transformed whole cells resulted in cybrid clones which, when injected into newborn rat pups, isogenic with those from which the cell culture was initiated, yielted tumors in 51% of the animals injected compared to 92% of the animals injected with the tumorigenic parent. Those animals that did develop tumors from the cybrid cells survived longer than those injected with cells from the tumorigenic parent. Thus, the cybrid, formed of cytoplasm from both parents, was less tumorigenic than the malignantly transformed parent cell. When reconstituted cells were prepared by fusing cytoplasts from normal cells with karyoplasts from malignantly transformed cells, a situation in which essentially all of the cytoplasm of the reconstituted cell is derived from normal cells, the tumorigenic phenotype was extinguished. This work was supported in part by United States Public Health Service grant CA12056, and grant CA09100 from the National Cancer Institute, Bethesda, MD. This work is partial fulfillment for the degree of Doctor of Philosophy for B.A.I.     

Differential effects of calcium deprivation on the cytoskeleton of non-tumorigenic and tumorigenic rat liver cells in culture

Normal rat liver T51B epithelial cells and Morris no. 7795 hepatoma cells growing exponentially were exposed for 24 h to standard medium containing low (0.02 mM) calcium, a concentration which drastically reduces the proliferation of normal but not tumour cells. Cell surface morphology was examined by scanning electron microscopy (SEM); and the distribution and organization of microtubules, cytokeratin and vimentin filaments, and microfilaments were analysed by indirect immunofluorescence microscopy using specific antibodies. Calcium deprivation caused the loss of intercellular cohesion in both cell types and the appearance of some microvilli and blebs, particularly on tumour cells. However, marked differential (normal vs tumour cells) effects on the organizational integrity of the cytoskeleton fibrillar network were observed. Extracellular calcium deprivation led to a particular rearrangement of microtubules, and a perinuclear accumulation of cytokeratin and vimentin filaments in normal, but not in tumour cells. A massive concentration of actin-containing microfilaments was observed in the cell periphery and blebs of hepatoma cells. In the light of the possible involvement of calcium in controlling cytoskeleton assembly, the differing cytoskeletal changes of the two cell types may be linked to their diffferent proliferative capabilities in low-calcium medium.     

Heterogeneity of intercellular adhesion in rat liver cells in culture

The intercellular homotypic adhesive properties of 14 clones derived from a nontumorigenic rat liver epithelial cell line (LEC), derived from neonatal Fischer rats, were examined and compared to those of the hepatoma H4-II-E cell line. Each clone was assayed also for the degree of chromosomal aneuploidy and the ability to grow in soft agar. Over 100-fold differences in adhesive properties were observed among the clones, but no correlation was observed between the degree of aneuploidy in the clones and intercellular adhesive properties. The parent LEC cell line and the clones derived from it were unable to grow in soft agar. The H4-II-E cells showed negligible capacity to reaggregate after dissociation into single cells and these cells readily formed colonies in soft agar. Many of the LEC clones were similar to the H4-II-E cells in their adhesive properties, which suggests that reduced cell-to-cell adhesiveness per se is not a necessary prerequisite of epithelial cells to be able to grow independent of anchorage. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) of concanavalin A (Con A)-binding glycoproteins in the "most adhesive" clone 67 and the "least adhesive" clone 201 showed markedly elevated amounts of acidic 105 and 67-kDa glycoproteins in clone 67. Proteins with similar migration patterns in 2D-PAGE have previously been reported to participate in specific homotypic intercellular adhesion of liver cells. The Con A-binding glycoprotein pattern in H4-II-E cells was markedly different from that of LEC cells with a set of six proteins missing and nine proteins appearing new in the H4-II-E cells. It is suggested that, in addition to identifying known epithelial cell polypeptides, systematic screening of cell surface-associated glycoproteins in normal and transformed epithelial cells in vitro and in vivo may lead to identification of novel polypeptides intimately associated with the transformed phenotype.     

Identification of protein IT of the intestinal cytoskeleton as a novel type I cytokeratin with unusual properties and expression patterns

A major cytoskeletal polypeptide (Mr approximately 46,000; protein IT) of human intestinal epithelium was characterized by biochemical and immunological methods. The polypeptide, which was identified as a specific and genuine mRNA product by translation in vitro, reacted, in immunoblotting after SDS-PAGE, only with one of numerous cytokeratin (CK) antisera tested but with none of many monoclonal CK antibodies. In vitro, it formed heterotypic complexes with the type II CK 8, as shown by blot binding assays and gel electrophoresis in 4 M urea, and these complexes assembled into intermediate filaments (IFs) under appropriate conditions. A chymotrypsin-resistant Mr approximately 38,000 core fragment of protein IT could be obtained from cytoskeletal IFs, indicating its inclusion in a coiled coil. Antibodies raised against protein IT decorated typical CK fibril arrays in normal and transformed intestinal cells. Four proteolytic peptide fragments obtained from purified polypeptide IT exhibited significant amino acid sequence homology with corresponding regions of coils I and II of the rod domain of several other type I CKs. Immunocytochemically, the protein was specifically detected as a prominent component of intestinal and gastric foveolar epithelium, urothelial umbrella cells, and Merkel cells of epidermis. Sparse positive epithelial cells were noted in the thymus, bronchus, gall bladder, and prostate gland. The expression of protein IT was generally maintained in primary and metastatic colorectal carcinomas as well as in cell cultures derived therefrom. A corresponding protein was also found in several other mammalian species. We conclude that polypeptide IT is an integral IF component which is related, though somewhat distantly, to type I CKs, and, therefore, we propose to add it to the human CK catalogue as CK 20.     

Human thymic epithelial cells are frequently transformed by retroviral vectors encoding simian virus 40.

The thymic microenvironment contains a mixture of phenotypically distinct epithelial cells of varied functions, some of which are unknown. In an attempt to understand their relevance to T cell differentiation in the thymus, human thymic epithelial cell clones from both fetal (SM3-SM5) and postnatal (SM6) thymus were produced by using a defective recombinant retroviral vector encoding the simian virus 40 large T antigen and the neomycin resistance gene. The presence of keratins 8 and 18, desmosomes, and tonofilaments confirmed the epithelial origin of the cell strains. The cells expressed Thy-1 and HLA-Class I at high levels, showed weak-expression antigens defined by TE3B and A2B5, and low to negligible levels of the MR19-defined molecule. When compared with the phenotype of thymic epithelial cells in situ, the cell strains appear to be derived from neuroendocrine components in the outer cortical region of the human thymus. The use of retroviral vectors to transform human thymic epithelium was considerably more efficient than transfection with a plasmid carrying the origin of replication-defective SV40 large T gene. In the latter case, only two cell strains with subcapsular epithelial phenotypes were derived from fetal thymus. With the retroviral vectors, epithelial cell strains could, for the first time, be generated from human postnatal thymus as well as from fetal thymus.     

Normal and Ha-ras-1 oncogene transformed Buffalo rat liver (BRL) cells show differential resistance to cytoskeletal protein inhibitors.

In the present study, using immunofluorescence microscopy, we have demonstrated that normal and Ha-ras-1 transformed Buffalo rat liver (BRL) cells which were exposed to cytoskeletal protein inhibitors, showed a differential resistance of their microfilament and microtubule networks. One hour exposure of normal BRL cells to 10(-5) M cytochalasin B provoked a clear and already total breakdown of actin filaments. However, at this concentration of cytochalasin B, the microfilaments of transformed BRLHO6T1-1 cells were not seriously affected; a higher cytochalasin B concentration (> or = 2 x 10(-5) M) was required to induce a significant breakdown of microfilaments in these transformed cells. The two cell lines also demonstrated differential microtubule stability when they were treated with either colchicine or triethyllead. Three hours exposure to 10(-6) M of either antimicrotubule agents was sufficient to disrupt the microtubules of normal BRL cells, without affecting their counterparts in the transformed BRLHO6T1-1 cells. A 10-fold higher drug concentration (10(-5) M) was required to induce microtubular breakdown in the transformed BRL cells. The differential stability of microfilaments and microtubules in normal and transformed BRL cells that was observed could not be attributed to a differential internalization of the agents, as shown by experiments on the uptake of [3H]-cytochalasin B and triethyllead. In addition, the transformed BRLHO6T1-1 cells did not express altered actin and tubulin isoforms, as demonstrated by isoelectric focusing followed by immunoblotting analysis. We conclude that the transformation of BRL cells with the Ha-ras-1 oncogene results in a greater stability of microfilaments and microtubules, leading to a structurally firmer cell shape.(ABSTRACT TRUNCATED AT 250 WORDS)     

Cells transformed by a wide variety of agents express higher abundance levels of some cellular RNA species

A cDNA-cloned library was prepared from mRNA synthesized by SV40-transformed mouse cells. Eleven cDNA clones were selected based on their ability to hybridize higher levels of mRNA in SV40-transformed 3T3 cells than in 3T3 cells. These cDNA clones were employed to screen the steady-state levels of cytoplasmic RNAs in a wide variety of viral (SV40, polyoma, adenovirus, and Rous sarcoma virus) and nonviral (methylcholanthrene, embryonal carcinoma) transformed cell lines. Two of the cDNA clones—A17 and 104—detected greater than 40–100-fold higher levels of mRNA in all the transformed cell lines tested when compared to nontransformed cells (3T3, C3HEF). The levels of mRNA complementary to these two cDNAs were regulated in a temperature-sensitive fashion (87–100-fold) in both SV40tsA- and RSV ts-src-transformed murine cell lines. These two cDNA clones detected greater than 100-fold, higher levels of complementary RNA derived from SV40 tumor tissue than in normal mouse liver. RNA species complementary to cDNA clones A17 or 104 were not detected in either actively growing nontransformed cells or in serum-stimulated 3T3 cells. The abundance levels of mRNAs detected by these two cDNA clones appear to be regulated 100-fold or greater by the transformed state, independent of the transforming agent. The higher levels of these RNA species detected in transformed mouse cells appear not to be solely regulated by the state of growth of nontransformed cells.     

Intermediate filaments in rat ovarian surface epithelial cells: changes with neoplastic progression in culture.

Interrelationships between neoplastic progression and the expression of intermediate filaments were examined in primary cultures, immortal lines, and Kirsten murine sarcoma virus (KiMSV) transformed lines of rat ovarian surface epithelial (ROSE) cells. Immunofluorescence microscopy revealed abundant keratin filaments in all cells of primary cultures. In immortal, nontumorigenic lines, keratin filaments were detected in fewer cells, in smaller numbers, and in microscopically altered forms. The percentage of keratin-positive cells ranged from 4 to 54%. Its expression was inversely proportional to cell density. Keratin expression was similar in the two immortal lines, although one had retained a monolayered epithelial growth pattern resembling primary cultures, while in the other the growth pattern of the cells was more atypical. The two KiMSV-transformed lines were previously shown to produce tumors in vivo that resemble human ovarian endometrioid stromal sarcomas. In spite of this histologic appearance, the proportion of keratin-positive cells in these cells was increased over the immortal lines. Keratin expression was unrelated to cell density, and keratin in most virally transformed cells was limited to few, fine filaments. In thymidine-labelled immortal and virus-transformed cultures stained for keratin, no correlation was found between keratin expression and proliferative activity. The keratin profiles of primary and immortal cultures were identical on Western blots, with subtypes ranging from 52 to 66 kDa. The two virally transformed lines lacked some of the subtypes. Vimentin networks were faint or absent in primary cultures. In the immortal and the virus-transformed lines, neoplastic progression was associated with increasing vimentin expression but with no changes in filament morphology and distribution. The results show that the abnormalities in intermediate filament expression that accompany immortalization do not preclude the retention of a normal epithelial morphology and growth pattern in this cell type. Furthermore, the number of intermediate filaments and their intracellular distribution appear to be altered at an earlier stage in neoplastic progression than those mechanisms that select for specific keratin subtypes, or those that respond to regulation by cell density. Finally, the presence of keratin in the KiMSV-transformed lines examined in this study supports the hypothesis that human ovarian stromal sarcomas can arise in the OSE.     

Expression of alpha(4)beta(7) integrin defines a distinct pathway of lymphoid progenitors committed to T cells, fetal intestinal lymphotoxin producer, NK, and dendritic cells

During embryogenesis, the Peyer's patch anlagen are induced by a cell population that produces lymphotoxin (LT) alpha(1)beta(2) following stimulation of IL-7Ralpha. In this study, we show that the LT-producing cell is localized within the IL-7Ralpha(+) and integrin alpha(4)beta(7) (alpha(4)beta(7))(+) population in the embryonic intestine. Lineage commitment to the LT producer phenotype in the fetal liver coincides with expression of alpha(4)beta(7). Before expression of alpha(4)beta(7), the potential of IL-7Ralpha(+) population to generate B cells is lost. However, the progenitors for T cells and LT producer cells reside in the IL-7Ralpha(+)alpha(4)beta(7)(+) cells, but during subsequent differentiation, the potential to give rise to T cells is lost. This IL-7Ralpha(+)alpha(4)beta(7)(+) population migrates to the intestine, where it induces the Peyer's patch anlagen. When stimulated with IL-15 or IL-3 and TNF, the intestinal IL-7Ralpha(+)alpha(4)beta(7)(+) population can differentiate into fully competent NK1.1(+) NK cells or CD11c(+) APCs. Expression of alpha(4)beta(7) is lost during differentiation of both lineages; IL-7Ralpha expression is lost during NK1.1(+) cells differentiation. A newly discovered lineage(-)IL-7Ralpha(+)c-Kit(+)alpha(4)beta(7)(+) population in the fetal liver is committed to T, NK, dendritic, and fetal intestinal LT producer lineage, the latter being an intermediate stage during differentiation of NK and dendritic cells.     

Rearrangement of antigen receptor genes is defective in mice with severe combined immune deficiency

A process unique to lymphocyte differentiation is the rearrangement of genes encoding antigen-specific receptors on B and T cells. A mouse mutant (C.B-17scid) with severe combined immune deficiency, i.e., that lacks functional B and T cells, shows no evidence of such gene rearrangements. However, rearrangements were detected in Abelson murine leukemia virus-transformed bone marrow cells and in spontaneous thymic lymphomas from C.B-17scid mice. Most of these rearrangements were abnormal: approximately 80% of Igh rearrangements deleted the entire Jh region, and approximately 60% of TCR beta rearrangements deleted the entire J beta 2 region. The deletions appeared to result from faulty D-to-J recombination. No such abnormal rearrangements were detected in transformed tissues from control mice. The scid mutation may adversely affect the recombinase system catalyzing the assembly of antigen receptor genes in developing B and T lymphocytes.