The isolation and selected properties of blood monocytes

The interaction between human monocytes and red cells. Binding characteristics

Red cells coated with IgG globulin were bound firmly to human mononuclear cells and formed rosettes. Rosette formation occurred when red cells were coated with IgG attached either immunologically (anti-D, anti-penicillin, or Donath-Landsteiner antibodies) or nonimmunologically with chromic chloride; no attachment was observed with cells coated with albumin. Rosette formation was blocked by pretreatment of white cells with sulfhydryl-binding reagents. Metabolic inhibitors did not prevent red cell adherence. White cells of other primates demonstrated a high degree of species specificity. Ultrastructural studies showed that the predominant leukocytes involved in rosette formation were monocytes, but some cells with characteristics of lymphocytes also formed rosettes. Considerable interdigitation of cell surfaces occurred at attachment sites and bound red cells appeared deformed. Thus, these studies confirm the presence of specific surface receptors for IgG on human monocytes and suggest that such receptors may provide a mechanism by which large numbers of red cells are eventually destroyed.

Human monocytes and macrophages. Interaction with antigen and lymphocytes

PPD-sensitized monocytes and macrophages from tuberculin-positive subjects are both capable of inducing blastogenic transformation of autologous lymphocytes. Incorporation of thymidine-(3)H and morphological transformation were always greater in lymphocyte cultures containing macrophages than in those containing monocytes. More lymphocytes entered the first detectable S phase in cultures containing macrophages. Lymphocyte DNA synthesis occurred as early as 40 hr of culture and always in cells in contact with mononuclear phagocytes. By 120-144 hr, many transformed lymphocytes were free in suspension; at the same time, the "immunological cluster" had increased greatly in size and contained transformed and untransformed lymphocytes. The greater effectiveness of macrophages at induction of lymphocyte transformation may be related to the efficiency of this cell type at trapping antigen and its effectiveness at making contact with and binding lymphocytes.

Canine cutaneous histiocytoma. A light and electron microscopic study

Cutaneous histiocytomas from 4 dogs were examined by light and electron microscopy. A large (up to 10 μ in diameter) mononuclear cell with prominent filiform processes of the plasma membrane predominated. Its cytoplasm contained relatively small amounts of endoplasmic reticulum and mitochondria, only occasional lysosomes, fibrils, most obvious in the perinuclear region, and small amounts of cytoplasmic debris. Acid phosphatase was not detected.

Fibroblasts and collagen formed a small part of the lesion, except at the junction with surrounding dermis, where fibers were plentiful.

The morphologic features of the lesion are compatible with the suggestion that the predominant cell is of histiocytic type.

Lactoferrin, an iron-binding protein in neutrophilic leukocytes

Lactoferrin, an iron-binding protein previously shown to occur in many external secretions, is identified as one of the major proteins present in human and guinea pig neutrophilic polymorphonuclear leukocytes. The identification of this protein in leukocyte extracts was based upon a comparison of its electrophoretic, antigenic, and iron-combining properties with the corresponding properties of the same protein isolated from human and guinea pig milk. Immunochemical quantitations showed that lactoferrin occurs in human neutrophilic leukocytes at the concentration of 3 microg per 10(6) cells. Tissue cultures from guinea pig bone marrow and spleen actively synthesized the protein, as shown both by net production of lactoferrin and incorporation of labeled amino acids into the protein. Immunohistochemical data indicate that lactoferrin first appears in myeloid cells at the stage of the promyelocyte.

Lung alveolar histiocytes engaged in antibody production

After introduction of antigen (sheep red blood cells) into rabbit lung alveoli by intrapulmonary or intratracheal injection antibody forming and releasing cells are found in subsequently evoked alveolar exudates. Intratracheal immunization results in slightly delayed antibody formation with a remarkably low involvement of mediastinal lymph nodes. At peak appearance of plaque-forming cells (PFC) in alveolar exudates 20–26 per cent of PFC are histiocytes or monocytes by microscopic and ultrastructural criteria. Plaque-forming histiocytes are less differentiated forms, different from typical macrophages. Their antibody production is sensitive to puromycin and to a lesser degree to actinomycin-D. In contrast to lymphoid PFC, some of these histiocytes are sensitive to a phagocyte-destructive agent-silica. Among the PFC, plasma cells and (early after immunization) activated lymphocytes and blasts are conspicuous in comparison with the overall composition of the cell populations of the alveolar exudate and mediastinal lymph node. It is calculated that 1 in 100–500 plasma cells and 1 in 20,000–100,000 histiocytes give demonstrable haemolysin formation during the peak of cellular response. This is suggested as the difference between the specialized and occasional or `primitive' antibody forming cell.

The IgG receptor: an immunological marker for the characterization of mononuclear cells

Using red cells sensitized with an IgG anti-Rh₀ antibody, an IgG receptor was demonstrable on human monocytes, hepatic macrophage and splenic macrophage preparations. The receptor was uniformly lacking on lymphocytes, lymphoid cell lines and lymphocytes stimulated with phytomitogens in vitro. The integrity of this receptor was demonstrated on monocytes obtained from patients with `acquired' agammaglobulinaemia, chronic granulomatous disease and acute monocytic leukaemia. There was no direct correlation between the presence of the receptor and the fine structure of the cells studied. It is proposed that this receptor is an immunological marker for identification of mononuclear cells.

Cytotoxic effects of leukocyres triggered by complement bound to target cells

Chromium-51-labeled chicken erythrocytes (E), treated with rabbit anti-Forssman antibody (A) and the first four (C1-4) or the first seven (C1-7) components of human complement (C), released isotope upon exposure to human leukocytes. Isotope release from EACJ-7 cells proceeded more rapidly and was more extensive than that from EACI-3 cells. Lysis of these cells was suppressed by pretreatment of leukocytes with antimycinA. Monocyte-enriched leukocyte preparations affected both types of target cell-complement intermediates, whereas purified lymphocytes lysed EACI-7 cells but not EACI-3 cells.

The uptake, storage, and intracellular hydrolysis of carbohydrates by macrophages

The exposure of cultivated mouse macrophages to sucrose (0.009-0.03 M) leads to the formation of large phase- and electron-lucent, acid phosphatase-positive vacuoles in the perinuclear region. The vacuolization process and the uptake of sucrose-(14)C is blocked by inhibitors of pinocytosis and stimulated by calf serum in the medium. These results suggest the uptake of sucrose by pinocytosis and its subsequent segregation and storage in secondary lysosomes. The addition of sucrose also increases the total content of three macrophage lysosomal hydrolases. The addition of invertase to the environment of sucrose-laden macrophages leads to the prompt shrinkage of the sucrose-containing lysosomes. This is accompanied by the intracellular hydrolysis of sucrose to fructose and glucose residues which are promptly excreted into the medium. The uptake of invertase, as indicated by the shrinkage of sucrose-containing vacuoles, is blocked by inhibitors of pinocytosis. No effect was noted when invertase was added to macrophages laden with Ficoll, a polysucrose which is not hydrolyzed by the enzyme. The influence of other carbohydrates was then investigated. Monosaccharides with molecular weights up to 220 did not produce vacuolization. However, a certain number of di-, tri-, and tetrasaccharides produced vacuolization identical with that of sucrose. Each of the disaccharides which produced vacuolization was resistant to the complement of macrophage hexosidases, whereas those that were ineffective were degraded by either macrophage or serum enzymes. The addition of beta-glucosidase to cellobiose-laden macrophages resulted in the shrinkage of vacuoles but did not alter the vacuoles of sucrose containing cells. The ability of small, neutral carbohydrates to produce lysosomal swelling is dependent upon both molecular weight and their resistance to lysosomal hydrolases.

Human monocytes: distinct receptor sites for the third component of complement and for immunoglobulin G

Human monocytes contain two distinct receptor sites, one specific for the third component of complement (C'3), the other for immunoglobulin G(gammaG). The two receptors may function either independently or cooperatively in the induction of phagocytosis. Ingestion of erythrocytes coated with immunoglobulin M antibody requires a relatively large number of bound C'3 molecules per cell. Ingestion of erythrocytes sensitized with gammaG antibody is independent of complement; however, the reaction is inhibited by concentrations of gammaG far below those in normal serum. Inhibition by gammaG-globulin is overcome by a relatively small number of bound C'3 molecules per cell. The two monocyte receptors exert a cooperative effect on ingestion by monocytes of erythrocytes coated with gammaG antibody in the presence of inhibitory amounts of free gammaG.

The interaction of human monocytes and lymphocytes

Monocytes isolated from the peripheral blood of tuberculin-positive and tuberculin-negative donors were exposed to PPD, extensively washed, and incubated with autologous or homologous lymphocytes. Lymphocyte transformation was measured morphologically and by incorporation of (14)C-labeled thymidine. Monocytes from tuberculin-positive subjects induced transformation of autologous lymphocytes in 19 of 29 experiments. Studies to define the optimal conditions of exposure to monocytes to PPD and to autologous lymphocytes showed that viable, metabolically intact monocytes are required. A ratio of only 1 monocyte to 100 lymphocytes sufficed to induce transformation; neutrophils were inactive. In general, PPD-sensitized monocytes failed to induce transformation of homologous lymphocytes from either tuberculin-positive or tuberculin-negative subjects. Direct contact between monocytes and lymphocytes was required for consistent transformation, and islands of transforming lymphocytes were observed around a central core of monocytes.

The origin and kinetics of mononuclear phagocytes

The origin and turnover of efferent populations of mouse mononuclear phagocytes has been described. Mononuclear phagocytes were defined as mononuclear cells which are able to adhere to glass and phagocytize. In vitro labeling studies with thymidine-(3)H showed that monocytes in the peripheral blood and peritoneal macrophages do not multiply and can be considered end cells in a normal, steady state situation. However, the mononuclear phagocytes of the bone marrow appear to be rapidly dividing cells. This conclusion was supported by in vivo labeling experiments. A peak of labeled mononuclear phagocytes of the bone marrow was found 24 hr after a pulse of thymidine-(3)H. This was followed, 24 hr later, by a peak of labeled monocytes in the peripheral blood. From these experiments it was concluded that the rapidly dividing mononuclear phagocytes of the bone marrow, called promonocytes, are the progenitor cells of the monocytes. Labeling studies after splenectomy and after X-irradiation excluded other organs as a major source of the monocytes. Peak labeling of both the blood monocyte and peritoneal macrophages occurred at the same time. A rapid entry of monocytes from the blood into the peritoneal cavity was observed, after a sterile inflammation was evoked by an injection of newborn calf serum. These data have led to the conclusion that monocytes give rise to peritoneal macrophages. No indications have been obtained that mononuclear phagocytes originate from lymphocytes. In the normal steady state the monocytes leave the circulation by a random process, with a half-time of 22 hr. The average blood transit time of the monocytes has been calculated to be 32 hr. The turnover rate of peritoneal macrophages was low and estimated at about 0.1% per hour. On the basis of these studies the life history of mouse mononuclear phagocytes was formulated to be: promonocytes in the bone marrow, --> monocytes in the peripheral blood, --> macrophages in the tissue.

Cellular hypersensitivity and cellular immunity in the pathogensis of tuberculosis: specificity, systemic and local nature, and associated macrophage enzymes

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Studies on the nonspecific depression of the immune response

Calf serum has been shown to suppress the primary immune response to erythrocytes and some bacterial antigens in mice if administered prior to and not after immunization. The importance of the route of iniection of antigens and immunosuppressant is indicated. It is suggested that immunosuppression is achieved by phagocytosis and enyzmatic destruction of the injected antigen by peritoneal macrophages. A similar mechanism is probably involved in the type of immunosuppression induced by PHA.