Temperature-induced variations in the surface topology of cultured lymphocytes are revealed by scanning electron microscopy

Temperature effects on lymphocyte transformation invitro

Phytohemagglutinin (PHA)-induced transformation of normal rat peripheral lymphocytes has been studied at a wide range of culture temperatures (4 degrees C to 42 degrees C). Lymphocyte transformation was maximum at 37 degrees C while insignificant stimulation was observed between 4 degrees C and 30 degrees C. Temperatures above 37 degrees C produced sub=optimal transformation as measured by synthesis of DNA and protein, and appearance of lymphoblasts. Binding studies using 125I-PHA indicate that the low temperature inhibition of lymphocyte transformation could be a result of excess lectin (being available as a result of low temperature) bound to the cell surface, preventing the initiation of the molecular events associated with transformation.

Acute lymphoblastic leukemia: a study of 25 cases by scanning electron microscopy

Cells from 25 cases of acute lymphoblastic leukemia (ALL) were studied under the scanning electron microscope (SEM). In 24 of the cases, the vast majority of circulating leukaemic cells had few microvilli. Villous cells were rarely encountered and prominent ridge-like profiles and ruffled membranes were not seen. Only six cases were studied by immunological techniques and four of the cases were of the null type while in two the cells bore detectable T-markers. It seems that ALL is almost always associated with the presence of cells with few microvilli in the peripheral circulation, differing in this respect from most cases of CLL. Although circulating leukaemic lymphocytes with few microvilli are sometimes seen in CLL, the most frequent cell type encountered is a more villous lymphocyte. Differences between leukaemic cells from patients with ALL, CLL and non-lymphoblastic leukaemias are discussed. It appears that SEM may help to distinguish lymphoblastic and nonlymphoblastic leukaemic cells in many instances and can be used as a useful adjunct to other modes of microscopy in the diagnosis of acute leukaemia.

Schistosoma mansoni: the occurrence of microvilli on the surface of the tegument during transformation from cercaria to schistosomulum

Microvilli are developed on the surface of Schistosoma mansoni schistosomula during penetration of the host skin; they form rapidly but are lost approximately 90 min after penetration. Identical microvilli are also formed on schistosomula which have penetrated a mouse skin preparation in vitro, and on schistosomula prepared by mechanical separation of the tail from the body of the cercaria. The microvilli, which are limited by the trilaminate tegumental membrane of the cercaria, eventually degenerate and are cast off from the surface of the tegument. There is little change in the surface area of the schistosomulum at this time, and the formation and loss of microvilli coincides with the replacement of the cercarial tegumental membrane by the new heptalaminate membrane. It is suggested that during the cercaria/schistosomulum transformation, some intramembraneous components of the original cercarial membran e may migrate into the new heptalaminate membrane and thus be retained, while other peripheral components such as the glycocalyx are almost certainly lost.

Physical and metabolic requirements for early interaction of poliovirus and human rhinovirus with HeLa cells

Attachment, ""tight binding'' and eclipse of radioactive poliovirus 2 (P2) and human rhinovirus 2 (HRV 2) were investigated. The activation energy for attachment of both HRV2 and P2 was about 13 kcal/mol. HRV2 differed from P2 in two respects: the Arrhenius plot for attachment of HRV2 showed a break at 15 to 19 degrees C when the cells were first treated several hours at 0 degrees C, and attachment of HRV2 was inhibited by treatment of cells with metabolic poisons able to reduce cellular ATP by more than 90%. Tight binding was determined by isolation of a specific P2-membrane complex or by loss of EDTA dissociability of HRV2. Tight binding of both viruses was slowed by 0.01 M iodoacetamide but not by 0.02 M F-; F- plus 0.002 M CN- slowed tight binding of HRV2 but not of P2. Eclipse, the irreversible alteration of parental virions, was detected by isolation of cell-associated subviral particles or by loss of cell-associated infectious virus. Eclipse of both viruses is slowed by iodoacetamide or F-. It seems likely that the early steps of infection with picornaviruses may be sensitive to alterations in the cell membrane produced by metabolic inhibitors or by treatment at low temperature.

The lymphocyte plasma membrane: locus of control in the immune response

The lymphocyte plasma membrane is the locus of events which control the immune response. T and B lymphocytes, which mediate cellular and humoral immunity respectively, show distinctive plasma membrane morphologies and cell surface receptors. The dynamic state of these plasma components is emphasized by their lateral mobility in the fluid plane of the membrane, as well as variation in their structure or expression as the lymphocyte proliferates and differentiates in response to stimulation by antigen or mitogens. The best understood membrane glycoproteins are surface membrane immunoglobulins that serve as antigen receptors on B cells, and the histocompatability-beta2 microglobulin complex that has an immunoglobulin-like structure. Other less well defined surface structures showing modulation during the cell cycle may affect growth regulation of proliferating lymphocytes. Some of these are shared by fetal and neoplastic cells. Major theories of lymphocyte signaling are discussed, and the early events in lymphocyte activation are reviewed. While a complete model encompassing all these early events is not yet possible, the central issues can be usefully discussed in term of receptor-transducer-effector concepts derived by strong parallels from a knowledge of hormone-membrane interactions.

The scanning electron microscopy of normal human peripheral blood lymphocytes

A study of the effects of various sample preparation techniques for scanning electron microscopy has been undertaken in an attempt to resolve conflicting descriptions of the surface topography of human peripheral blood lymphocytes. By fixing cells in suspension--a technique thought most likely to avoid the production of artefacts--no clearly defined morphological classification of lymphocytes could be made, and when T- and B-lymphocyte enriched preparations were studied their surfaces appeared similar. Both T- and B-rosetted cells showed identical morphological changes as a result of their interaction with red blood cells. The smooth cells described in other reports were found only under certain conditions of preparation. It is therefore not possible to distinguish between T- and B-cell populations, using the S.E.M., on the basis of surface morphology alone.

Revised seminology of the different mononuclear cells under scanning electron microscopy

Scanning electron microscopy shows that the thymus cell surface is not smooth but slightly undulated; this type of surface characteristic is found on the cells of several types of T-lymphocyte tumors such as T-cell lymphosarcoma, mycosis fungoides, and T-immunoblastic lymphosarcoma. The cell surface of Frabricius' bursa is covered with numerous short villi. They are found on the cells of several kinds of B-lymphocyte tumors, including B-cell chronic lymphoid leukemia, B-prolymphocytic lymphosarcoma, and B-immunoblastic lymphosarcoma. Mycosis fungoides cells frequently have a characteristic shape. Normal and myeloma plasma cells are similar in shape but their surface is covered with numberous characteristic tiny balls. Immunoblasts are twice the size of so-called small lymphocytes. In the blood and in the lymphocyte population transformed by mitogens, cell surfaces vary from completely smooth (with no undulations as in thymic cells) to villous, with short to very long villi. These variations are visible even when a constant technique and the critical-point drying method are used. Their significance, however, is not known.

A scanning electron microscopy and immunological study of 84 cases of lymphocytic leukaemia and related lymphoproliferative disorders

The surface features of cells from 84 cases of lymphocytic leukaemia, and related lymphoproliferative disorders are described as seen by scanning electron microscopy (SEM). Most of the 46 cases of CLL were shown to be B-derived, but rare cases of mixed B and T cell leukaemia and leukaemia with cells bearing both B and T markers were also encountered. Despite the existence of a spectrum of cell surface morphology, it was possible in many cases to identify a dominant cell type. Cells from cases of B derived malignancies were most frequently of the 'predominantly villous' type while a smaller proportion of cases were of the predominantly 'smoother' or 'mixed villous and smooth' type. Variations in surface morphology also occurred with progression of the disease. In most cases of acute lymphoblastic leukaemia (ALL) 'smoother' cells predominated. However, more cases of ALL and T derived leukaemia need to be examined before definite conclusions can be drawn concerning the surface of these cell types. This study also illustrates the importance of examining large numbers of cases of leukaemia, before conclusions are drawn concerning their surface features and indicates that SEM cannot consistently distinguish between leukaemic B and T cells. It will be of interest to determine whether the surface architecture of the leukaemic cell is related to the degree of cell differentiation and eventual prognosis in these cases.

Biochemical and enzymatic characterization of thymic and splenic lymphocyte plasma membranes from inbred rats

Purified splenic and thymic lymphocytes from the ACI and F344 strains of inbred rats were disrupted by controlled hypotonic treatment, and their plasma membranes were prepared by sucrose density gradient centrifugation. The plasma membrane preparations were highly purified as judged by the structural appearance of the smooth membrane vesicles, by the 10- to 15-fold enrichment of 5'-nucleotidase, which cytochemically localized exclusively in the plasma membranes of intact lymphocytes, by the high cholesterol to phospholipid molar ratio (0.7-1.0), and by the very low specific activities of the enzymes associated predominantly with mitochondria, lysosomes, and endoplasmic reticulum. The protein and the lipid contents of the membranes were 48-55 and 37-48%, respectively. The total lipid content of plasma membranes was characteristically higher in thymic than splenic lymphocytes from both ACI and F344 strains. The specific activity of 5'-nucleotidase was similar in splenic lymphocyte membranes of the ACI strain, and in both the thymic and splenic lymphocyte membranes of the F344 strain. In contrast, the thymic lymphocyte membranes in the ACI strain showed half as much 5'-nucleotidase specific activity. Cytochemical results indicated that the 5'-nucleotidase is located on the outside surface of the lymphocyte plasma membranes.

Human lymphocytes: similarity of B and T cell surface morphology

When viewed by scanning electron microscopy human lymphocytes fixed in suspension and processed with minimal cell loss appear uniformly covered with short microvilli. Contrary to previous reports, lymphocytes from subpopulations selectively enriched for T cells are villous and indistinguishable from B lymphocytes. Whereas lymphocyte surface architecture can change rapidly and substantially in response to environmental modifications, such as contact with an underlying surface, these alterations are similar for both B and T cells and do not serve to distinguish these subpopulations.

A congenital haemolytic anaemia with thermal sensitivity of the erythrocyte membrane

Microspherocytes, measuring 2-3 mum in diameter, and cells with blunted projections or triangular in shape characterized the erythrocoyte morphology in three children with congenital haemolytic anaemia. Since the erythrocyte morphology resembled that associated with thermal injury, heat-induced changes in erythrocyte morphology and membrane composition were studied. Erythrocytes developed filaments and spheroid bodies which fragmented, resulting in microspherocyte transformation. Normal cells required exposure to 49 degrees C, whereas the patients' cells fragmented at 45 degrees C. Fragmentation was also observed during incubation of patients' cells at 37 degrees C for 17h. The heat-induced transformation of the patients' cells was associated with an increase in the membrane cholesterol:phospholipid and cholesterol:protein ratios. The phospholipid:protein ratio was unchanged. This suggests that fragmentation produces a selective loss of membrane components. Splenectomy ameliorated the haemolytic process. We propose that the patients' red-cell morphology is the result of in vivo fragmentation, and that the spleen is the major site of microspherocyte and poikilocyte destruction.

Cell surface immunoglobulin. XII. Localization of immunoglobulin on murine lymphocytes by scanning immunoelectromicroscopy

The localization of immunoglobulin (Ig) on the surface of murine splenic lymphocytes has been studied with the scanning electron microscope (SEM), using a rabbit F(ab')2 hybrid antibody directed against mouse Ig and tobacco mosaic virus (TMV) with TMV as a morphological marker. 35% of spleen cells and 3% of thymus cells were labeled by this method. Labeled cells were usually small lymphocytes with moderate numbers of microvilli. The Ig molecules were randomly distributed on the lymphocyte surface, appearing on microvilli as well as on the smooth surface of the cell.

'Hairy' cell leukaemia (leukaemic reticuloendotheliosis): a scanning electron microscopic study of eight cases

Eight cases of 'hairy' cell leukaemia (leukaemic reticuloendotheliosis) were evaluated by scanning electron microscopy. The surface of critical-point-dried 'hairy' cells was characterized by prominent and exaggerated broad-based, ruffled membranes and scattered small clusters of stub-like microvilli. The surface morphology resembled that of normal and leukaemic monocytes, but differed from that of normal and leukaemic lymphocytes. Some cells with features of both lymphocytes and monocytes were difficult to categorize; the overall impression of the surface architecture of most 'hairy' cells suggests, however, that they are related to the monocytic series. From the examination of these cases it is evident that scanning electron microscopy may be used as a means of distinguishing chronic lymphocytic leukaemia from 'hairy' cell leukaemia on the basis of surface ultrastructure.

Hapten-sandwich labeling. II. Immunospecific attachment of cell surface markers suitable for scanning electron microscopy

A hapten-sandwich procedure has been used for immunospecific labeling of cell surface antigens with markers visible by scanning electron microscopy. Antihapten antibody was used to link hapten-modified tobacco mosaic virus, bushy stunt virus, or hemocyanin to hapten-modified human erythrocytes. The antihapten antibody bridge was also used to link the hapten-virus marker to hapten-modified antibodies against mammary tumor virus on mouse mammary tumor cells, or against immunoglobulin receptors on mouse splenic lymphocytes. In all cases, labeling was highly specific. With this technique, it is possible to (a) compare morphological features of cells bearing differing cell surface antigens, and (b) examine the arrangement of specific antigenic sites on a cell surface or their distribution relative to membrane structures such as microvilli.

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.

Scanning electron microscopy of tobacco mosaic virus-labeled lymphocyte surface antigens

The study of surface antigen by immunoelectron microscopy has been hampered by the fact that thin sections of cells provide only a view of the cell perimeter in an essentially two- dimensional fashion. Although the reconstruction of the entire cell from serial sections has been accomplished (1), it remains too exacting a technique and will find only exceptional application. Carbon-platinum replicas (2) allow the inspection of larger surface areas and therefore are better suited for studying the distribution of antigens (3). But since only relatively smooth surfaces will yield stable replicas, cells with large numbers of microvilli are not amenable to this technique. Despire its limited resolution, scanning electron microscopy (SEM) seems to be the method of choice because it can provide a view of almost half of the surface of a cell close to its natural configuration, particularly after critical point or freeze drying (4, 5). Immunological-labeling methods have not yet been routinely applied to SEM although both latex spheres (6) and hemocyanin (7) have been used with some success. The optimal visual marker should possess the following properties: be of a distinctive shape, chemically stable, and have per se a low binding affinity for cell surfaces. Tobacco mosaic virus (TMV), a marker with which we are familiar in transmission electron microscopy (8), seems to meet these demands; it has rod-like shape and defined dimensions (15 x 300 nm) and in addition it can easily be distinguished from surface microvilli. As the hybrid antibody technique (9) is also applicable to TMV, we have attempted to combine such immunological labeling with SEM. We present evidence that surface antigens can indeed be visualized by SEM, using the TMV marker in conjunction with the hybrid antibody technique.

New immunolatex spheres: visual markers of antigens on lymphocytes for scanning electron microscopy

New immunochemical reagents consisting of antibodies bound to small latex spheres were used as visual markers for the detection and localization of cell surface antigens by scanning electron microscopy. Cross-linked latex spheres of various sizes from 300 to 3,4000 A in diameter were synthesized by aqueous emulsion copolymerization of methacrylate derivatives containing hydroxyl and carboxyl functional groups. Proteins and other molecules containing primary amino groups were covalently bonded to the acrylic spheres under a variety of mild conditions by the aqueous carbodiimide, cyanogen bromide, and glutaraldehyde methods. For use in the indirect immunochemical-labeling technique, goat antibodies directed against rabbit immunoglobulins were bonded to the spheres. These immunolatex reagents were shown to bind only to cells (red blood and lymphocytes) which had previously been sensitized with rabbit antibodies against cell surface antigens. Mouse spleen lymphocytes with exposed immunoglobulins on their surface (B cells) were labeled with these spheres and distinguished from unlabeled or T lymphocytes by scanning electron microscopy. The distribution of Ig receptors on lymphocytes was also studied using the spheres as visual markers. When lymphocytes were fixed with glutaraldehyde and subsequently labeled with the immunolatex reagents, a random distribution was observed by scanning electron microscopy; a patchy distribution was observed when unfixed lymphocytes were used. These results are consistent with studies using ferritin-labeled antibodies (S. De Petris and M. Raff. 1973. Nature [Lond.]. 241:257.) and support the view that Ig receptors on lymphocytes undergo translational diffusion. In addition to serving as visual markers for scanning electron microscopy, these latex spheres tagged with fluorescent or radioactive molecules have applications as highly sensitive markers for fluorescent microscopy and as reagents for quantitative studies of cell surface antigens and other receptors.

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.

Scanning electron microscopy of human lymphocyte-sheep erythrocyte rosettes

Human lymphocytes of known B or T derivation were examined by scanning electron microscopy (SEM) before and after rosetting with SRBC. After collection of the cells onto silver membranes the samples were prepared for SEM by the critical point drying method. Sheep RBC frequently underwent sphero-echinocyte transformation and multiple projections extended from their surfaces. This was readily noticeable after storage of SRBC in the cold and washing in Hanks, but more prominent after rosetting. These erythrocyte surface alterations were less apparent when freshly withdrawn cells were used. Spontaneous sheep erythrocyte rosettes (E-R), a marker for human T lymphocytes, were prepared with normal peripheral blood lymphocytes (PBL), thymic cells, and cultured T cells. EAC-rosettes (EAC-R), used to identify B lymphocytes with complement receptors, were prepared with normal PBL and cultured B cells. The majority of rosetting T lymphocytes had generally smooth surfaces while about 20% had an intermediate number of microvilli and 15% were more villous and indistinguishable from villous B cells. Studies of rosetting thymocytes and cultured T cells however indicated that the surface of some T cells alters on rosetting, becoming more villous and thus account for the higher numbers of villous T cells seen in E-rosettes. Point to point contact sites between SRBC and T lymphocytes were more frequent than broad zones of attachment. The majority of rosetting B lymphocytes had multiple microvilli, about 25% had a moderate number of microvilli and less than 10% had smooth surfaces similar to those of most T cells. Areas of contact between EAC and B lymphocytes were frequently broad zones of attachment. The study confirms that in many cases B and T lymphocytes can be distinguished by their surface architecture as seen under the SEM; however, about 20% of rosetting B and T cells have similar surfaces with intermediate numbers of surface microvilli and cannot be distinguished by SEM without parallel immunologic identification.

Morphology, motility, and surface behavior of lymphocytes bound to nylon fibers

Mouse B lymphocytes that were specifically bound to dinitrophenylated bovine serum albumin on nylon fibers exhibited continuous morphological changes, whereas bound T lymphocytes remained more or less spherical. Cinematomicrographic studies showed that the shape changes were associated with local and global movements, although the attached cells did not translocate along the fiber. Cap formation induced by anti-immunoglobulin was always found to be opposite to the point of attachment. The movements and the shape changes were prevented by cytochalasin B and colchicine. Treatment with these agents did not prevent cap formation but led to randomization of the position of the caps with respect to the fiber. Exposure to concanavalin A or attachment of cells to concanavalin A fibers prevented both movement and patch and cap formation, suggesting that cellular structures regulating the mobility of various receptors are altered by binding to concanavalin A fibers. These observations also indicate that interactions of local areas of the lymphocyte surface with certain ligands and substrates can strongly affect the movement and morphology of the entire cell.