Mouse thymus-independent and thymus-derived lymphoid cells. II. Ultrastructural studies

Application for PCR technology to subtractive cDNA cloning: identification of genes expressed specifically in murine plasmacytoma cells

We describe a simple method for preparing a renewable source of subtractive cDNA which can be used as a hybridization probe or as insert which can be cloned into a variety of convenient vectors. This has been done by ligating a double-stranded oligonucleotide to each end of double-stranded subtractive cDNA, and then using this oligonucleotide sequence to amplify the heterogeneous population of cDNA molecules using the polymerase chain reaction and thermostable Taq DNA polymerase. This method improves the chances for identifying cDNA clones representing low abundance mRNAs that are expressed differentially. Using this approach, we have identified cDNA clones which detect three different low abundance mRNAs that are expressed in mouse plasmacytoma cell lines but not in mouse pre-B or B lymphoma cell lines.

Identification of consensus genes expressed in plasmacytomas but not B lymphomas

We have combined subtractive cDNA and PCR technologies to construct and analyze a plasmacytoma minus a highly differentiated B lymphoma subtractive cDNA library. We detected no plasmacytoma-specific clones by hybridization with differential cDNA probes or the subtractive insert. However, random selection of 115 clones has identified 16 quantitatively subtractive and 39 qualitatively subtractive clones. From these clones we have identified 8 potentially interesting genes. One quantitatively subtractive clone (clone 315) identifies an mRNA that is expressed in most plasmacytoma cell lines, but is expressed at an approximately 10-fold lower level in B and pre-B lymphoma cell lines; preliminary evidence suggests that the expression of this gene is increased by IL-6. From the 31 unrelated qualitatively subtractive clones, we have identified two classes of genes that are expressed in one or none of 8 B lymphomas examined: 1) those expressed in most plasmacytoma and pre-B lymphoma cell lines (clone 70 and clone 260); and 2) those expressed in most plasmacytoma cell lines, but not in any of the ten pre-B lymphomas examined (clones 251, 289A, 289B, 326, 291).

Quantitative ultrastructure of cytolytic lymphocytes mediating allograft rejection in the mouse. I. Cellular alterations in T lymphocytes during specific target cell lysis

A quantitative ultrastructural analysis of cytolytic T lymphocytes (CTL) is presented which allows both the distinction of these cells from normal T lymphocytes and permits the demonstration of ultrastructural alterations of putative CTL following interaction with target cells (TC). Alloreactive CTL were generated in C57BL/10 mice receiving intraperitoneal fibroblastic allografts and target-binding splenic lymphocytes (TBSL) were concentrated by specific immunoadsorption on fibroblast monolayers. TBSL were subjected to ultrastructural quantification either at the onset of TC interaction or following 30 or 60 min incubation at 37 degrees C. By means of simple stereological relationships it was shown that, in comparison with normal, non-cytolytic splenic T lymphocytes, TBSL were slightly larger cells, displaying around 60% more cytoplasm, a similarly-sized nucleus and approximately triple the volume of Golgi apparatus. During the first 30 min of interaction with TC, the target binding surface of the TBSL plasma membrane decreased in area. This change was accompanied by a polarization of the TBSL towards the target. Incubation of lymphocytes with TC for a further 30 min resulted in a general polarization of lymphocytic cellular constituents away from the TC. These results were only attainable by objective quantitative analysis and are discussed in relation to possible mechanisms of CTL-mediated lysis.

Evidence for cytotoxic T-lymphocyte-target cell interaction in brains of mice infected intracerebrally with lymphocytic choriomeningitis virus

Murine lymphocytic choriomeningitis is a T-cell-mediated pathologic immune phenomenon. The name of this experimental illness was derived from the principal histopathologic alterations of the central nervous system (CNS) of adult mice infected intracerebrally with lymphocytic choriomeningitis virus, i.e., lymphocytic infiltrations of plexus choroidei and meninges. The general assumption that the main event in the pathogenesis is damage to virus-infected target cells by cytotoxic T-lymphocytes is plausible but direct evidence is scarce. We have studied the ultrastructural alterations of both types of cells that are thought to participate in this immunopathologic interaction. Lymphocytes with signs of T-cell transformation were first evident on day 4 after infection. One day later, lymphoblasts, often extending uropods and containing cytoplasmic dense and compound multivesicular bodies, predominated. They were sometimes seen in intimate contact with connective tissue cells of the leptomeninx and epithelial cells of the choroid plexuses which were shown to be infected by immunofluorescence procedure. Lymphoblasts occasionally invaginated the cytoplasm of the putative target cells with cytoplasmic processes, and were even found inside the latter, exhibiting the phenomenon of emperipolesis. Lymphocytic transformation was at its maximum 6 days after infection. At this time, individual leptomeningeal cells and groups of plexus epithelial cells showed signs of cytolysis, and in a few instances these damaged cells were in close spatial association with lymphoblasts. Similar observations have been reported by others who studied the interaction between cytotoxic T-lymphocytes and their appropriate targeted cells in vitro. We interpret our findings as providing direct evidence for the assumption that one link in the chain of events leading to the cerebral form of lymphocytic choriomeningitis of the mouse is damage to virus-infected leptomeningeal and plexus cells by cytotoxic T-lymphocytes.

Stereological analysis of the ultrastructure in isolated human T and non-T lymphoid cells. I. Description of method and data on normal blood lymphocytes

Stereological techniques were applied to isolated and purified normal human T and non-T lymphocytes from the peripheral blood, allowing a quantitative characterization of the average cell and its subcellular components in each population at the ultrastructural level. From electron micrographs taken at two levels of magnification and subjected to point counting procedures and measurements on a Kontron Videoplan analyser, absolute and relative data comprising volumes, surfaces and ratios were obtained. The stereological model proved efficient in establishing important differences between the two lymphocyte subsets regarding features generated from the whole cell as well as from the nuclear and cytoplasmic compartments. Thus the average T cell compared to the non-T cell possessed the following qualities: a smaller cell volume and cell surface area due to a smaller cytoplasmic volume and surface area; a lower nuclear euchromatin-heterochromatin volume ratio indicating a greater amount of heterochromatin in the nucleus; a smaller volume and surface area of rough ER, and (to a less extent) a smaller amount of Golgi apparatus, dense bodies and residual cytoplasm. The rare occurrence of parallel tubular arrays were seen in the non-T fraction only, and dense bodies were more often clustered in T cells. The differences are discussed in immunological and functional terms.

A fluorescence study on the mobility of surface antigens of untreated tumor cells and of tumor cells undergoing cell-mediated lysis

Heterologous (rabbit) antibodies were raised against murine P-815 mastocytoma cells of DBA/2 origin. Antisera and IgG preparations were highly cytotoxic, whereas Fab fragments thereof lost all activity. Fab fragments also showed a much lower avidity than IgG, both for tumor and normal DBA/2 and C57 spleen cells as measured by the release of iodinated Fab and IgG. Both preparations bound specifically to P-815 cells since they were capable of inhibiting T cell-mediated target cell lysis. The binding of IgG and monovalent Fab fragments was studied by fluorescence. Rhodamine-coupled IgG bound homogeneously in the cold and quickly formed patches upon warming but did not form caps even after prolonged incubation at 37 degrees C. Rhodamine-coupled Fab fragments also bound homogeneously. Their distribution was unaltered after incubation at 37 degrees C even when tumor cells formed uropod-like tails. Fab fragments, however, could be induced to cap with a second and third antibody layer. P-815 cells labeled with rhodamine-coupled Fab fragments were incubated with cytolytic T cells (CTL). The conjugates formed between CTL and fluorescent target cells were observed. No gross redistribution of surface antigens on target cells was observed even at late stages of the lytic process. CTL, therefore, do not seem to operate via a redistribution of surface antigens.

Membrane asymmetry. A survey and critical appraisal of the methodology. I. Methods for assessing the asymmetric orientation and distribution of proteins

This and the companion article are aimed at surveying the methods used for the study of membrane asymmetry. The techniques employed for the assessment of the asymmetric distribution and orientation of membrane proteins are reviewed in this article, whereas those pertaining to the unequal distribution of lipids are detailed in the companion paper. The use of immunological techniques and lectins, functions of proteins and their perturbations, chemical reagents, enzymatic isotopic labeling and enzymatic cleavage of membrane proteins and physical techniques are discussed and illustrated using recent examples of their application. Whenever appropriate, problems involving crypticity and non-availability or non-reactivity of functional sites, relevant chemical functions or protein fragments to appropriate ligands, reagents or modifying enzymes are envisaged and possible modification of the exposure of proteins during preparation of ghosts and other drawbacks are discussed, the use of different techniques and control experiments in conjunction is recommended for a more realistic assessment of the distribution and orientation of proteins.

Ultrastructural studies of peripheral blood lymphocytes in T cell-depleted rabbits. A scanning and transmission electron microscopic analysis

Density separation of purified peripheral blood leucocytes from T-cell depleted rabbits on a linear Ficoll-metrizoate gradient has been applied to obtain different leucocyte fractions. Two lymphocyte fractions separated on density seem to have different characteristics, both morphologically and immunologically. In this study these two fractions have been characterized ultrastructurally by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and a relationship has been established between the surface architecture (SEM), the cell size (SEM/TEM) and surface-Ig/C3-receptors (LM, light microscopy). Finally three types of lymphocytes have been described in the two lymphocyte fractions separated on density. Morphometric information such as cell size, cell shape, eu-/heterochromatin ratio in the nucleus and the nucleus-/cell ratio have been correlated to the stage of activation of the B lymphocyte in a representative density separation.

Activation of human T-lymphocytes. A kinetic and stereological study

Stereological data of phytohaemagglutinin (PHA)-activated human T-lymphocytes were recorded at intervals (12 to 72 h) together with biochemical (isotope-uptake, lymphotoxin-release) and morphological measurements. About 98% of the cells were activated 12 h after PHA-stimulation. The activation phase lasted less than 48 h, i.e., cells entering the activation phase within 12 h were at their activation maximum by 48 h. The activated cell increased in size. The nuclear/cytoplasmic-ratio decreased. Most of the cytoplasmic organelles developed in phase with the increase of cytoplasmic volume. After 48 h, mitotic figures were frequently seen. Due to the increasing number of secondary, activated daughter cells, parameters of most cytoplasmic components declined between 48 and 72 h. Structural changes in the nucleus preceded the 3H-leucine uptake, which had not reached its maximum after 72 h of incubation. The 3H-leucine uptake started as early as 12 h after culture initiation, and its increase was proportional to the increasing polyribosome density. No maximum uptake was reached up to 72 h, but the development of structural components related to this uptake was at its maximum at the end of the activation phase (48 h). The formation of bound ribosomes occurred subsequent to the enlargement of the surface of the rough endoplasmic reticulum. Initial polysome formation occurred at the expense of existing free ribosomes.

The development of extranodal lymphoid follicles in experimental bronchopneumonia

Extranodal formation of lymphoid follicles was morphologically studied in experimental bronchopneumonia. Control gnotobiotic mice had no peribronchial lymphoid follicles and only lymphatic vessels were traced from the terminal bronchiolar region toward larger bronchi. During the week after intranasal inoculation of mycoplasma pulmonis, lymphoid follicles developed in the terminal portion of the lymphatics by the accumulation of small lymphocytes. A loose network of mesenchymal cells and early infiltration of macrophages, following stromal edema, seemed to play an important role in the early accumulation of lymphocytes. Blastic transformation was seen frequently in the center of the accumulated lymphocytes. Two weeks after inoculation plasma cells emerged conspicuously in the periphery of the lymphoid follicles, and the acute phase of bronchopneumonia began to subside. Typical germinal centers with tingible body macrophages and dendritic reticulum cells developed when the bronchitis persisted in a chronical manner.

Microcinematographic and electron microscopic analysis of target cell lysis induced by cytotoxic T lymphocytes

A study was carried out to determine the sequence of events of T-cell mediated target cell lysis in microcinematography and electron microscopy. Highly efficient cytotoxic T lymphocytes (CTL) were generated in vivo and in vitro using preimmunized spleen cells and purification procedures. Such CTL were highly specific. This specificity correlated well with the number of adhesions formed between CTL and targets and this criterion was used to study killer-target cell interaction. Microcinematography showed that target cell lysis at the single cell level, despite time variations, could be clearly separated into three phases: (a) a recognition phase, visible by random crawling of CTL over the target cell surface until firm contact was established; (b) a post-recognition phase, during which firm contact between CTL and target was maintained without gross modification of either cell; (c) a phase of target cell disintegration, mainly characterized by vigorous blebbing of the cell membrane resulting in a motionless carcass of the target cell but not in its total dissolution. Only later this carcass decayed and formed a necrotic ghost. Electron microscopic observations were put into sequence according to microcinematography. Post-recognition phase was characterized by a tight apposition of the membranes of CTL and target cell. No gap junctions could be observed. During target cell disintegration, profound cytoplasmic and nuclear changes occurred simultaneous with surface blebbing. Most noticeable were extensive internal vacuolization, mitochondrial swelling, nuclear pycnosis and dissolution of the nucleolus. These observations suggested that target cell lysis does not start with a surface phenomenon similar to complement lysis, but a process involving practically the whole cell simultaneously. It is conceivable, therefore, that the signal from the CTL is transmitted across the target cell, and that the switch to sudden cell death is manipulated deep inside the cell.

Morphological study of autologous rosettes (A-RFC)

The morphology of autologous rosette forming cells (A-RFC) has been studied by light and electron microscopy. Autorosette forming cells were obtained from the spleen of adult thymectomized (ATx) or nude mice, and from neonatal thymus grafts during the regeneration phase. Among the autorosettes seen by light microscopy, 76% of them were formed by lymphoid cells which included a high proportion of large lymphocytes (48%). Electron microscopy study performed after isolation of A-RFC by micromanipulation demonstrated that 74% were formed by large lymphoid cells with an immature nucleus. The finding of such large-sized lymphoid cells with immature nuclei is in agreement with our previous results indicating that A-RFC might belong to an immature T cell class.

Recognition of antigens by T lymphocytes

The present review briefly summarizes our knowledge of antigen-specific B and T lymphocyte receptors. Antigen-specific receptors on mammalian B lymphocytes are mainly monomeric IgM and IgD consisting of conventional immunoglobulin heavy and light chains. The nature of the T lymphocyte receptor which can specifically recognize antigens is not yet fully defined. However, it seems that conventional light chains do not participate in the build up of this receptor, and that the receptor is made up of heavy chains of a new immunoglobulin class which has to be further characterized and which we call Tau-chain. The variable region of the T lymphocyte receptors share idiotypic determinants with the corresponding B lymphocyte receptors. The possible linkage between the T cell idiotypes present on the Tau-chains and molecules which are under the control of genes of the Major Histocompatibility Complex of the species are discussed. In the last part of the review two methods for the induction of specific transplantation tolerance in adult animals are described. These methods are based on the concept that T lymphocytes reactive against alloantigens bear idiotypic determinants against which a specific auto-immune response can be initiated.

Morphology of lymphatic cells and of their derived tumours

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The pattern of lymphocytes in the thymus and spleen after labeling with 3H-thymidine and 3H-deoxycytidine

Adult male untreated mice (NMRI) were investigated after radioactive labeling with 3H-thymidine and 3H-deoxycytidine to find out whether the lymphocytes in the cortex and medulla of the thymus as well as in the perifollicular and periarteriolar regions of the spleen show a labeling pattern which allows a classification into T- and B-lymphocytes. The percentages of radioactively labeled small lymphocytes and their mean grain counts were determined. The percentages of radioactively labeled small lymphocytes after 3H-TdR and 3H-CdR showed no significant differences in both splenic zones. The grain counts over the lymphocyte nuclei in the periarteriolar zone showed lower values after 3H-TdR than after 3H-CdR. The lymphocytes in the perifollicular zone were strongly labeled with 3H-TdR and weakly labeled with 3H-CdR. In the thymus medulla, lymphocytes were weakly labeled with 3H-thymidine and strongly labeled with 3H-CdR. In the cortex no significant differences were observed. 75 to 80% of the small lymphocytes in the peripheral blood were weakly and 20-25% strongly labeled after 3H-TdR. Therefore there are similarities in the radioactive labeling pattern of thymic medulla lymphocytes and that of small lymphocytes of the periarteriolar zone of the spleen by both DNA precursors. The small lymphocytes in the peripheral T-dependent tissue zones, for example in the spleen, as well as in the mixed lymphocyte population of the peripheral blood can be differentiated from the B-lymphocytes through the difference in the amount of incorporation of 3H-thymidine and 3H-deoxycytidine.

Stereological model system for free cells and base-line data for human peripheral blood-derived small T-lymphocytes

T-lymphocytes derived from human peripheral blood and passed through a nylon-wool column, were employed to develop and test a new stereological model system for free spherical cells, allowing a quantitative characterization of the cell and its components at the ultrastructural level. Electron micrographs were recorded in a hierarchical manner at three different levels of magnification and subjected to point counting procedures. The resulting parameters were expressed in relation to various reference compartments, both absolute and relative. Results indicated that the average volume of a small, non-activated T-lymphocyte was 103.8 micron3, the nuclear volume 47.5 micron3 and the cytoplasmic volume 55.9 micron3. On the average, the cytoplasm contained 30 mitochondria, 0.7 micron3 RER-cisternae, 0.2 micron3 cisternae and vesicles of the Golgi apparatus and about 231,000 free ribosomes (most of them single). The ratio of eu- to heterochromatin volume was 0.5. The design and application of the stereological model system are discussed with regard to dynamic studies of a variety of free cells, such as macrophages, neutrophilic granulocytes and various lymphocytes.

The surface morphology of mitogen-stimulated human peripheral blood lymphocytes

The changes occurring in surface morphology during the transformation of normal peripheral blood lymphocytes by phytohaemagglutinin (PHA) are described and the surface ultrastructure of the PHA-induced blasts is compared with that of pokeweed mitogen (PWM)-and rabbit anti-beta2-microglobulin antiserum-induced blasts. Both mitogen-specific and non-specific changes were observed and their possible relationship to the activation of lymphocyte subpopulations is discussed. Similar surface characteristics found in various tissue lymphoid cells are also described.

Electron microscopic morphometric analysis of human T and B peripheral blood lymphocytes

Using the system of morphometric analysis described in this paper, human peripheral blood T and B lymphocytes, labeled with specific surface markers, can be compared on different analytical levels. They show differences in their surface and the eccentricity of cells, in the relative surfaces occupied by peripheral and central condensed chromatin, in the average surface of the central chromatin clumps and in the number of perichromatin granules per nuclear surface. The morphometric analysis reveals the importance of examining the nuclear and the surface parameters in the characterization of lymphocytes, confirming that a detailed analysis of the nuclear characteristics can contribute to the identification of T and B lymphocytes by transmission electron microscopy.

Diphenylhydantoin interstitial nephritis. Roles of cellular and humoral immunologic injury

A child with diphenylhydantoin hypersensitivity developed an associated interstitial nephritis. Circulating autoantibody of the IgG class which reacted with normal human tubular basement membrane was linearly deposited along host renal TBM. Cell-mediated immunity to the DPH antigen was also present. In addition, deposits of DPH were demonstrated along the renal TBM. It is suggested that initial alteration of host renal TBM by DPH deposition with secondary immune injury directed at the DPH-TBM antigen may have altered the TBM or uncovered new antigenic sites, rendering it susceptible to further injury on an autoimmune basis.

Ultrastructural studies of leucocytes which form rosettes with homologous erythrocytes in human auto immune haemolytic anaemia

Leucocytes which form rosettes with himologous erythrocytes in auto-immune haemolytic anaemia, infectious mononucleosis and following the stimulation of lymphocyte cultures with PHA have been studied by electron microscopy. The studies showed that the predominant homologous rosette forming cell was lymphocytic and the evidence favoured the conclusion that they were non-immune in nature. This identification does not classify the lymphocyte as thymus or bone marrow derived. Just under half (44%) of the total lymphocytic RFC had perinuclear microfilaments and limited clearing of the plasma of ribosomes close to the cell membrane. These features are consistent with activated T lymphocytes. The remainder of the lymphocytic RFC had no features which allowed their identification as T or B cells. The form of contact between lymphocytic RFC and erythrocyte was mainly of a pointlike nature, with little deformation or invasion of the attached erythrocytes. Monocytes were the only other type of cell encountered with any frequency. Their prime distinguishing feature was the deformation of attached red cells which they caused.

Ultrastructural labeling of lymphocyte surface immunoglobulin: the preparation and use of soluble immune complexes as indirect immunoelectromicroscopic markers

2 distinct macronuclear markers, ferritin and hemocyanin, may be used in a mixed anti-globulin labeling reaction to localize lymphocyte surface immunoglobulin (Ig) determinants by transmission electron microscopy. Soluble immune complexes of the marker molecules (antigen) are prepared by complexing with specific antiserum in 40 to 50 x antigen excess; uncomplexed Ig is removed by ultrascentrifugation and/or gel filtration chromatography. Immunoelectrophoresis, spectrophotometry and passive hemagglutination inhibition assay are used to determine the purity and amounts of antibody-antigen in the purified immune complexes. For immunoelectron microscopic labeling, the immune complex markers are coupled to lymphocyte surface Ig by an indirect anti-Ig or anti-allotype antibody linkage. Labelled Ig determinants at 0 degrees C or in the presence of sodium azide are visualized as small patches of marker molecules on the lymphocyte surface membrane. This EM labeling method results in much more consistent and generally higher percentages of surface Ig positive cells (60 to 70% of rabbit peripheral blood lymphocytes) than the percentages obtained using other methods, such as immunofluorescence or autoradiography. If the lymphocytes are warmed to 37 degrees C in the absence of azide the labeled surface Ig determinants undergo rapid endocytosis; endocytotic vesicles containing marker molecules are visible. This mixed anti-globulin immunoelectronmicroscopic labeling system may be used to localize a wide variety of antigens on different cell surfaces.

Activated T-cell in autoimmune haemolytic anaemia

In 12 of 14 patients with clinically active autoimmune haemolytic anaemia high levels (9-78%) of homologous and autologous rosetting cells were found in the peripheral blood. In 10 of these patients, who were observed over a period of 2 years, the levels bore a direct relationship to the activity of the disease. The cells so identified were T-lymphocytes. The role of cells, identified by this method in AIHA, is discussed.

Macrophage-lymphocyte cluster formation in the medullary sinus of lymph node after immunization with sheep red blood cells (SRBC)

Normally the lymphatic sinuses of the lymph node are loosely packed with lymphocytes and free macrophages as well as with macrophages adhering to the fibrocellular trabeculae. After immunization with SRBC cluster formation occurs in the medullary sinuses of rats between a central macrophage and peripherally located lymphocytes. These rosette-like clusters are nearly identical with the clusters found during primary and secondary immune response against SRBC in vitro and seem to be the in vivo equivalent for the same immune response.

The reaction of cells with anti-actin sera in relation to the amount of cellular actin

The staining pattern of anti-actin sera on various cells smeared on glass was compared to the relative amount of cellular actin estimated by SDS-polyacrylamide-gel electrophoresis with subsequent scanning of the gel. Although the cells showed a varying stainability the actin content was fairly constant. Thus, the staining differences reflected changes in the organization of cellular actin rather than actual differences in the amount of actin.

Immunopathology of coeliac disease

Coeliac disease may be defined as a condition in which there is an abnormal jejunal mucosa with loss of villi, which improves morphologically after treatment with a gluten-free diet. Pathologically, there is damage to the jejunal enterocytes, with hyperplasia of crypt cells so that overall enteropoiesis is increased. On conventional or scanning electron microscopy the enterocytes are markedly abnormal. Histochemically, the normal punctate appearance of the lysosomes is lost and sensitive lysosomal enzyme assays on mucosal biopsy samples using isopycnic centrifugation techniques show that there is an increase in total lysosomal activity with reduction in lysosomal latency. Studies following gluten feeding in patients whose mucosa has returned to normal after treatment with a gluten-free diet show that pathological abnormalities appear within 4--8 hours of gluten challenge. Complement together with extracellular IgM can be demonstrated in the lamina propria, suggesting the formation of immune complexes. In untreated coeliac disease there is a significant reduction in serum levels of C3 and C4. There is also evidence indicating the presence of immune complexes in the serum. Coeliac disease may therefore be an intestinal model of an immune complex disease, in which an antigen derived from gluten reacts with an antibody formed locally in the gut, fixing complement and causing damage to the enterocyte by activation of lysosomes.

Ultrastructure of cells infiltrating human kidney allografts

Cell infiltration is commonly observed in human renal allograft biopsies. This infiltration was investigated using electron microscopy for a more precise assessment of the nature of these cells. More than 3000 cells infiltrating twenty-five renal allograft biopsies were studied. Six cellular types were distinguished and a mean percentage of each type was calculated. Only one-half of these cells were normal or transformed lymphocytes (including small lymphocytes: 22-3 +/- 3-8%, 'intermediary' cells: 22 +/- 3-6%, blast-like cells similar to MLC transformed lymphocytes: 8-1 +/- 2-4%. A relatively high number of plasmocytes (12-4 +/- 2-5%) and a still higher percentage of macrophages (28-5 +/- 4-6%) were found. Granulocytes represented only 2 +/- 0-8%of the cell population. Variations of the mean percentage of these cellular types were studied in various clinical situations.

Accessibility to antibodies of acetylcholine receptors in the neuromuscular junction

Antibodies to the acetylcholine receptor are present in the serum of myasthenic patients but one does not know if, in vivo and in situ, they can penetrate the intact neuromuscular junction and block directly the receptor. The present experiments demonstrate that molecules the size of antibodies can reach acetylcholine receptor in situ. The mouse diaphragm with its intact neuromuscular junction was used as a source of acetylcholine receptor. The receptor was revealed either directly by iodinated alpha-bungarotoxin covalently coupled to IgG or indirectly, once labelled with cobra toxin, by iodinated anti-cobra toxin antibodies.

The differentiation of cytotoxic T lymphocytes in vitro: an ultrastructural study

T killer cells were identified morphologically in two different culture systems. The first system allowed identification by comparing under identical culture conditions two types of stimulation, one leading to cytotoxic activity levels that were very high (H-2 stimulation) and the other to levels which were practically nil (M-locus stimulation). A second system allowed identification by the use of a collaborative system in which relatively pure precursors of T killer cells were mixed with precursors of T amplifier cells from which they were distinguishable by their Thy-l antigen. In this latter case, surface labelling techniques had to be used. As in the in vivo situation, T killer cells were medium-sized pale cells with evidence of a well-developed secretory and motile apparatus. No evidence of highly active protein synthesis was found. Other T cells were dark and mainly derived from the T amplifier population, again consistent with in vivo findings. There was considerable background proliferation, even in the absence of any added antigen, and this included the formation of some well-developed plasma cells.

Ultrastructural studies of rabbit synovitis induced by autologous IgG fragments. II. Infiltrating cells in the sublining layer

The synovial sublining layer of rabbits with synovitis induced by intra-articular injection of cathepsin D digested autologous IgG fragments (Fab2) has been examined under the electron microscope. Twelve or more injections of autologous Fab2 led to chronic synovitis with dense mononuclear cell infiltrates containing lymphocytes, blastic cells, plasma cells and macrophages. In the infiltrates there was evidence that the lymphocytes had been activated prior to transformation into mature plasma cells. Indirect evidence suggests that T lymphocyte activation also occurred in these infiltrates. Cellular contacts between macrophages and lymphocytes or plasma cells as well as between M cells and lymphocytes were demonstrated. These contacts are tentatively interpreted as a feature of ongoing immune processes in the synovium.

Distribution of transplantation antigens on cell surfaces

Significant advances have been made over the past few years in elucidating the genetics, the chemical composition, and, more recently, the in situ relation of the major histocompatibility antigens of the mouse and man. Attempts to map the arrangement of individual antigens on the surface of cells have revealed that some antigens specified by a given subregion of both the H-2 and HL-A systems are in close proximity on the cell membrane and that attachment of antibody to one site to a certain degree blocks or inhibits the binding of antibody to the adjacent site. Allelic antigens in the H-2 system tend to inhibit binding. H-2D and H-2K antigens show either inhibition or noninteraction, possibly reflecting a cis-trans effect. Unlike with the H-2, inhibition of binding occurs only between HL-A antigens specified by homologous chromosomes. Also, a number of instances have been noted where inhibition of binding is unidirectional, possibly reflecting a polymeric nature of antigen or stratification of moieties at cell surface. Inhibition of antibody attachment between several alloantigenic systems on thymocytes in mice and also a variation in the mobility of the histocompatibility antigens suggest that the moieties bearing histocompatibility antigens are comprised of several gene products. Further work is needed to establish the validity of this assumption and to fully define the composition of these units. Ample data have been obtained from both biological and biophysical experiments to support the suggestion that single or multiple complexes of glycoproteins can move in the plane of the membrane. Although the composition of these cell membrane components remains a question, direct visualization by fluorescence and electron microscopy indicates that these moieties are small and, under natural conditions, distributed uniformly over the cell surface. Direct and indirect labeling techniques have shown that the complexes have no fixed position in the cell membrane and can be displaced laterally in the plane of the membrane without affecting the distribution of other surface molecules, such as sIg and species-specific antigens. Additional evidence suggests that H-2D and H-2K antigen complexes, as well as their gene products specified by different parent chromosomes, may be displaced separately. These observations are especially interesting and must be reconciled and data obtained by proximity analysis which indicate an association of some allelic products and possibly certain combinations of D and K antigens. Whether the differences noted in reactivity of the various surface antigens following attachment of antibodies are attributable to difference in size or to differences in the manner of their intercalation in the cell membrane remains to be elucidated. The rapid advances in elucidation of the molecular structure of biological membranes suggest that experimental work should be done on the biophysics of the structure of the antigenic sites and the mechanism of migration...

Macrophage-lymphocyte clusters in lymph nodes: a possible substrate for cellular interactions in the immune response

The lumens of the lymphatic sinuses in lymph nodes are traversed by fibrocellular trabeculae. Joined to these trabeculae were macrophages, which formed cell clusters with lymphocytes. It is proposed, based on structural similarities, that these cell clusters are the equivalent in vivo to those seen during primary and secondary immune responses in vitro. These intraluminal macrophages were located in the path of lymph-borne antigen, as well as in the path of newly formed and recirculating lymphocytes in sinuses. This would facilitate the possible interaction between macrophage-associated antigen and antigen-reactive lymphoid cells. The attachment of numerous lymphocytes to the surfaces of macrophages and the resulting cell clusters also afford increased opportunities for lymphocyte-lymphocyte contact.

Idiotype positive T cells visualized by autoradiography and electron microscopy

Anti-idiotypic antibodies were prepared in (CBA X C57BL/6)F1 hybrid mice by immunization either with CBA anti-C57BL/6 alloantiserum or with purified CBA thymus-processed lymphoid cells (T cells) Iodinated anti-mouse Ig or triple sandwich ferritin-labeling techniques served to visualize the reaction between idiotype and anti-idiotype. From 5 to 10% of purified CBA T cells appeared to carry receptors for C57BL/6 antigens. Heavily labeled cells had the morphology of small lymphocytes.

Morphological definition of thymocyte subpopulations

An attempt was made to distinguish immature from mature, immunocompetent thymocytes in the adult mouse using morphological criteria. All procedures enriching for competent thymocytes also enrich small cells whose morphology is very similar to the small thymocytes that have been described in the medulla of the thymus (Abe and Ito, 1970). A heterogeneity of competent thymocytes is likely since the enriched populations always contain a number of medium sized cells. These latter cells show spontaneous DNA-synthetic activity and are probably the source of thymus proliferative activity. Owing to their characteristic morphology these two cell types might represent the precursors for each of the two differentiated T cell types that have been found to occur in delayed type hypersensitivity (Matter, 1974).

The surface morphology of human B lymphocytes as revealed by immunoelectron microscopy

Surface immunoglobulins (sIg) were detected on human lymphocytes by immunoelectron microscopy with peroxidase-conjugated antibodies. Blood, marrow, and thymus cells from normal individuals and patients with lymphoproliferative disorders were examined. Samples were fixed before exposure to specific reagents. Normal lymphocyts with detectable sIg, i.e. B lymphocytes, were characterized by a villous surface; nonlabeled blood lymphocytes and thymocytes were smooth cells. Intermediate cells were also found which in sections appeared moderately villous and labeled, thus identified as B lymphocytes. Further evidence for a relationship between villous surface and sIg was given by the finding of a few lymphocytes with polar concentration of labeled microvilli. In chronic lymphocytic leukemia patients, most cells exhibited a villous surface with parallel variations of the number of microvilli and of anti-immunoglobulin-binding capacity. However, some labeled smooth blastic cells were also observed. On the other hand, abnormal lymphocytes from Sézary's syndrome which could exhibit segments of villous membrane had no detectable sIg. This study confirms that in most cases human B lymphocytes have a characteristic surface appearance and that the detection of sIg in normal lymphocytes correlates with the presence of microvilli.

Surface morphology of murine B and T lymphocytes: A comparative study by scanning electron microscopy

A variety of murine lymphocytes of known B or T derivation obtained from different lymphoid organs were prepared for scanning electron microscopy (SEM) by the critical point drying method after collecting the cells by aspiration onto silver membranes. Comparison of SEM appearances of cells prepared by this technique and serological classification according to surface antigens showed that most T cells had smooth surfaces with few microvilli, while many B lymphocytes were moderately to markedly villous. Further evidence for the above correlation was obtained by examining thymic cells and enriched B or T cell populations. Thymic cell suspensions containing less than 5% B cells showed over 80% generally smooth cells by SEM. Enriched T cell populations, obtained by mass cytolysis of lymph node preparations with anti-Ia or anti-Ig sera or by purification through nylon fiber columns, contained over 85% T cells, and more than 75% of them were of the smooth cell type. A similar correlation was noted for enriched B cell populations obtained by cytolysis of lymph node cells with anti-Thy-1 serum, and by lysis of EAC-rosettes. Over 90% of these cells were identified as B cells by immunologic methods and approximately 75% had moderate to markedly villous surfaces. The 15% difference can be accounted for by the existence of a subpopulation of smooth B cells. Direct observation of EAC-rosettes confirmed that most B cells had moderate to large numbers of surface microvilli and that less than 10% were smooth. It is possible that some of the smooth cells seen in enriched B cell populations may represent precursors or B lymphocytes at different stages of differentiation. These results indicate that murine T and B lymphocytes, like their human counterparts, can be recognized in many cases under the SEM on the basis of their surface morphology. Smoother B and more villous T cells are difficult to classify by SEM without parallel immunologic identification.

Nodular lymphoma: an ultrastructural study of its relationship to germinal centers and a correlation of light and electron microscopic findings

This study describes the ultrastructural findings in 16 cases of nodular lymphoma, and compares these with normal germinal centers in order to determine the possible germinal center origin of the lymphomas. Long branching desmosome-associated dendritic reticulum cells, characteristic of germinal centers, were found in all 16 cases of nodular lymphoma. Desmosomes were observed only between dendritic cells and not between lymphoid cells, and they were seen in only 1 of 7 cases of diffuse lymphoma. Cells comprising the nodular lymphomas share cytologic features, such as nuclear blebs and marked nuclear indentations, with germinal center cells. It appears that nodular lymphomas have a close anatomical relationship to germinal centers, although their actual origin from these sites is not established by this study. They are composed of lymphoid cells; we have no evidence to confirm the view that nodular lymphomas are derived from dendritic cells. Light and electron microscopic findings have been compared in order to establish the nature of large "histiocyte-like" cells in the nodular lymphomas. Many of these cells appear to represent transformed lymphocytes rather than histiocytes. They are more numerous in so-called mixed "histiocytic" lymphocytic lymphomas than in poorly differentiated lymphocytic lymphomas, which otherwise are ultrastructurally similar. This study casts doubt upon the existence of a mixed lymphocytic and histiocytic lymphoma within the spectrum of the nodular lymphomas, and indicates that a cytologic continuum exists between cells interpreted as poorly differentiated lymphocytes and those heretofore identified as histiocytes.

Macrophage-lymphocyte clusters in the immune response to soluble protein antigen in vitro. II. Ultrastructure of clusters formed during the early response

Macrophage-lymphocyte clusters are formed when lymph node cells and autologous peritoneal exudate cells from guinea pigs immunized with tubercle bacilli are cultured in the presence of purified protein derivative of tuberculin (PPD) for 20 h. We have studied the ultrastructure of these clusters employing transmission and scanning electron microscopy. The most simple macrophage-lymphocyte cluster consisted of one macrophage, one large central lymphocyte with a blastoid appearance attached to the macrophage with a broad area of contact, and from a few to more than 20 small peripheral lymphocytes attached to the central lymphocyte by their uropods. Some clusters were of more complex type, containing two or three macrophages or one macrophage with more than one central lymphocyte attached to the surface, but even in these clusters each peripheral lymphocyte was attached only to one central lymphocyte. By morphological criteria the peripheral lymphocytes were T lymphocytes.