Immuno-electronmicroscopical localization of a microvillus membrane disaccharidase in the human small-intestinal epithelium with monoclonal antibodies

The cellular localization of the human intestinal disaccharidase, sucrase-isomaltase, was visualized in ultrathin cryosections by the use of specific monoclonal antibodies [25] followed by protein A-gold. The principle site of immunoreaction concerned the microvillus membrane, which supports current concepts of the localization of these hydrolases. One antibody against sucrase-isomaltase also showed labeling of the Golgi apparatus, apical vesicles, and lysosomes, but not of the basolateral membrane. The labeling of the Golgi complex was uniform, suggesting the absence of accumulation of sucrase-isomaltase in cisternae during its passage through this organelle. Absence of labeling of the basolateral membrane appears to support the view that newly synthesized sucrase-isomaltase is transferred directly from the Golgi complex to the microvillus membrane, bypassing the basolateral membrane. However, the results do not exclude the possibility of a very rapid passage through the basolateral membrane. A substantial fraction of the sucrase-isomaltase occurred in lysosomes, which indicates that this organelle plays a major role in the catabolism of microvillar hydrolases. Transport of sucrase-isomaltase to lysosomes might occur by endocytosis or via the crinophagic pathway. The latter was previously postulated to reflect a regulatory mechanism at the post-Golgi level for the surface expression of microvillar membrane proteins.     

Ultrastructural localization of the circulating anodic antigen and the circulating cathodic antigen in the liver of mice infected with Schistosoma mansoni: a sequential study

The present study describes the ultrastructural localization of two important circulating schistosome antigens--the circulating anodic antigen (CAA) and the circulating cathodic antigen (CCA)--in livers of mice at various time intervals after infection with Schistosoma mansoni. For the demonstration of these antigens at the electron microscope level use was made of a direct, double immunogold labeling procedure, in which CAA-specific monoclonal antibodies, labeled with 5-nm gold particles, and CCA-specific monoclonal antibodies, labeled with 15-nm gold particles, were used. Both antigens were localized in granules and in inclusion bodies of Kupffer cells and granuloma macrophages and it was found that in these compartments the degree of 5- and 15-nm gold labeling increased with the duration of the infection. Sometimes gold particles were also encountered on the cell surface and in endocytotic vesicles of these cells, in endothelial cells, and in the space of Disse. From these data it was concluded that in the liver CAA and CCA were primarily accumulated in granules and inclusion bodies of Kupffer cells and granuloma macrophages. It is discussed whether at these locations both antigens are degraded by lysosomal enzymes and whether these antigens are complexed with antibodies.     

Intracellular localization and endocytosis of brush border enzymes in the enterocyte-like cell line Caco-2.

Immunoelectron microscopy was used to localize the brush border hydrolases sucrase-isomaltase (SI) and dipeptidylpeptidase IV (DPPIV) in the human colon carcinoma cell line Caco-2. Both enzymes were detected at the microvillar membrane, in small vesicles and multivesicular bodies (MVBs), and in lysosomal bodies. In addition, DPPIV was found in the Golgi apparatus, a variety of apical vesicles and tubules, and at the basolateral membrane. To investigate whether the hydrolases present in the lysosomal bodies were endocytosed from the apical membrane, endocytic compartments were marked with the endocytic tracer cationized ferritin (CF). After internalization from the apical membrane through coated pits, CF was first recovered in apical vesicles and tubules, and larger electronlucent vesicles (early endosomes), and later accumulated in MVBs (late endosomes) and lysosomal bodies. DPPIV was localized in a subpopulation of both early and late endocytic vesicles, which contained CF after 3 and 15 min of uptake, respectively. Also, internalization of the specific antibody against DPPIV and gold labeling on cryosections showed endocytosed DPPIV in both early and late endosomes. However, unlike CF, no accumulation of DPPIV was seen in MVBs or lysosomal bodies after longer chase times. The results indicate that in Caco-2 cells the majority of brush border hydrolases present in lysosomal bodies are not endocytosed from the brush border membrane. Furthermore, the labeling patterns obtained, suggest that late endosomes may be involved in the recycling of endocytosed DPPIV to the microvilli.     

Myocardial cell relationships during morphogenesis in normal and cardiac lethal mutant axolotls, Ambystoma mexicanum

Sarcomere formation has been shown to be deficient in the myocardium of axolotl embryos homozygous for the recessive cardiac lethal gene c. We examined the developing hearts of normal and cardiac mutant embryos from tailbud stage 33 to posthatching stage 43 by scanning electron microscopy in order to determine whether that deficiency has any effect on heart morphogenesis. Specifically, we investigated the relationships of myocardial cells during the formation of the heart tube (stage 33), the initiation of dextral looping (stages 34-36), and the subsequent flexure of the elongating heart (stages 38-43). In addition, we compared the morphogenetic events in the axolotl to the published accounts of comparable stages in the chick embryo. In the axolotl (stage 33), changes in cell shape and orientation accompany the closure of the myocardial trough to form the tubular heart. The ventral mesocardium persists longer in the axolotl embryo than in the chick and appears to contribute to the asymmetry of dextral looping (stages 34-36) in two ways. First, as a persisting structure it places constraints on the simple elongation of the heart tube and the ability of the heart to bend. Second, after it is resorbed, the ventral myocardial cells that contributed to it are identifiable by their orientation, which is orthogonal to adjacent cells: a potential source of shearing effects. Cardiac lethal mutant embryos behave identically during these events, indicating that functional sarcomeres are not necessary to these processes. The absence of dynamic apical myocardial membrane changes, characteristic of the chick embryo (Hamburger and Hamilton stages 9-11), suggests that sudden hydration of the cardiac jelly is less likely to be a major factor in axolotl cardiac morphogenesis. Subsequent flexure (stages 38-43) of the axolotl heart is the same in normal and cardiac lethal mutant embryos as the myocardial tube lengthens within the confines of a pericardial cavity of fixed length. However, the cardiac mutant begins to exhibit abnormalities at this time. The lack of trabeculation (normally beginning at stage 37) in the mutant ventricle is evident at the same time as an increase in myocardial surface area, manifest in extra bends of the heart tube at stage 39. Nonbeating mutant hearts (stage 41) have an abnormally large diameter in the atrioventricular region, possibly the result of the accumulation of ascites fluid. In addition, mutant myocardial cells have a larger apical surface area compared to normals.     

Molecular cloning of mouse tumour necrosis factor cDNA and its eukaryotic expression.

Tumour necrosis factor (TNF), released by induced macrophages, causes tumour necrosis in animals and kills preferentially transformed cells in vitro. mRNA induced in the established mouse monocytic PU 5.1.8 cell line by lipopolysaccharide, was converted into double-stranded cDNA and cloned in the pAT153 vector. Recombinant plasmids were screened by plus-minus hybridization and TNF-specific oligonucleotide probes constructed on the basis of partial amino acid sequences of rabbit TNF. A series of TNF specific clones were identified and confirmed by hybrid selection of mouse TNF-specific mRNA. The sequence codes for a 235 amino acids long polypeptide, of which 156 amino acids presumably correspond to the mature product. It can be concluded that mature mouse TNF is a glycosylated dimer. Biologically active TNF was secreted by both Cos-I and CHO-cells transfected with the chimaeric expression vector pSV2d2-mTNF containing the coding region of the mouse TNF cDNA gene.     

Poly I:C activated macrophages are tumoricidal for TNF-alpha-resistant 3LL tumor cells

Successive coculture of Lewis lung carcinoma (3LL) cells with T cell-derived lymphokines and LPS-activated macrophages has led to the acquisition of 3LL tumor variants (macrophage-resistant 3LL tumor variants (3LL-R)), manifesting a highly reduced sensitivity to the cytotoxic potential of T cell-derived lymphokines and LPS-activated macrophages and TNF-alpha. However, when 3LL-R cells are cocultured with Poly I:C-activated macrophages or with conditioned medium derived from these effector cells a significant lysis is observed. TNF-alpha participates in the cytolytic process of Poly I:C-activated macrophages as anti-TNF-alpha antibodies abolish the cytotoxic effect of these effector cells. In addition, class I IFN is involved because IFN-alpha and IFN-beta act synergistically on TNF-alpha mediated lysis of 3LL-R cells within 18 h. Moreover, anticlass I IFN antibodies abolish the cytolytic capacity of Poly I:C-activated macrophages. Hence, Poly I:C-induced macrophage-mediated cytolysis of 3LL-R cells may result from 1) the induction of macrophages by Poly I:C to secrete high amounts of TNF-alpha and class I IFN and 2) a synergism between IFN-alpha/IFN-beta and TNF-alpha on lysis of 3LL-R cells. This synergism does not result from a class I IFN-mediated enhancement of TNF-alpha receptor expression on 3LL-R cells. Therefore, the sensitivity of 3LL-R cells to TNF-alpha-mediated lysis in the presence of class I IFN is most probably regulated at the post-TNF-alpha receptor level. Furthermore, treatment of mice with Poly I:C strongly reduces the metastatic capacity of 3LL-R tumor cells, suggesting the participation of macrophages in the eradication of the established metastasis. Hence, TNF-alpha-resistant 3LL-R tumor cells may serve as a useful tool for the detection of alternative macrophage-related cytotoxins leading to the destruction of neoplastic cells both in vitro and in vivo.     

Mammomonogamus laryngeus (Railliet, 1899) infections in cattle from Sri Lanka

During one year 1249 male cattle were examined for Mammomonogamus laryngeus infections in the slaughterhouse at Kandy, Sri Lanka. The overall prevalence was 40% with only light monthly variations (34 to 52%). The infection rate was highest (47%) in 2 to 2.5 year old animals. In infected animals an average of 6.4 parasite pairs was found with higher numbers in older animals. The majority of worms were located on the posterior side of the epiglottis. Lesions observed were mucosal plugs at the site where the parasites were attached to the mucosa and moderate to severe erosions and ulcers in other zones.     

Host selection and survival of the parasitoidEncarsia formosa on greenhouse whitefly,Trialeurodes vaporariorum, in the presence of hosts infected with the fungusAschersonia aleyrodis

Successful control of greenhouse whitefly may be achieved by complementary activity of the parasitoidEncarsia formosa and the fungusAschersonia aleyrodis. One way to obtain an additive mortality effect of both entomopathogen and parasitoid would be achieved by the selection of healthy hosts by the parasitoid and rejection of fungus-infected hosts. Third and fourth instar larvae ofTrialeurodes vaporariorum which had been treated with a spore suspension ofA. aleyrodis 0, 4, 7, 10 or 14 days beforehand, were presented to female parasitoids. The parasitoids adopted the oviposition posture on untreated hosts as well as on treated hosts, irrespective of the different stages of infection in the hosts. However, significantly more hosts were parasitized byE. formosa in the control treatment than in the fungal treatment. The parasitoids offered treated hosts, showed rejection behaviour after probing on hosts showing detectable signs of infection (containing hyphal bodies or mycelium in the haemolymph). For instance, when hosts were offered seven days after spore treatment, the parasitoids showed an oviposition posture on a total of 83 (95.4%) out of 87 infected larvae, but laid only 4 eggs (4.6%). In contrast, on 48 (94.1%) out of 51 noninfected (or showing no detectable signs of infection) hosts an oviposition posture was adopted and 40 eggs (78.4%) were found after dissection. When infected hosts were encountered the oviposition posture lasted less than 1′40″ while rejection of non-infected hosts occurred after more than 1′40″. Other experiments were carried out offering treated hosts for 24 h to the parasitoids. The hosts were dissected afterwards. Again, significantly more eggs were laid in the non-infected hosts. When hosts were parasitized shortly after fungal spore treatment they were colonized by the fungus and the parasitoids did not develop. Transmission of the entomopathogen after probing infected hosts was observed to a limited extent. In conclusion,A. aleyrodis andE. formosa can be used together in a glasshouse situation. The parasitoid will be most effective when introduced more than seven days after application ofA. aleyrodis, because from that time onwards it is able to detect and reject fungus-infected hosts.     

The lepidopteran mitochondrial control region: structure and evolution

For several species of lepidoptera, most of the approximately 350-bp mitochondrial control-region sequences were determined. Six of these species are in one genus, Jalmenus; are closely related; and are believed to have undergone recent rapid speciation. Recent speciation was supported by the observation of low interspecific sequence divergence. Thus, no useful phylogeny could be constructed for the genus. Despite a surprising conservation of control-region length, there was little conservation of primary sequences either among the three lepidopteran genera or between lepidoptera and Drosophila. Analysis of secondary structure indicated only one possible feature in common--inferred stem loops with higher-than-random folding energies-- although the positions of the structures in different species were unrelated to regions of primary sequence similarity. We suggest that the conserved, short length of control regions is related to the observed lack of heteroplasmy in lepidopteran mitochondrial genomes. In addition, determination of flanking sequences for one Jalmenus species indicated (i) only weak support for the available model of insect 12S rRNA structure and (ii) that tRNA translocation is a frequent event in the evolution of insect mitochondrial genomes.