EFFECTS OF ANTICELLULAR SERUM ON PHAGOCYTOSIS AND THE UPTAKE OF TRITIATED THYMIDINE AND URIDINE BY HELA CELLS

Palmitate-derivatized antibodies can function as surrogate receptors for mediating specific cell-cell interactions

The observation that exogenously supplied agents can bypass intrinsic recognition mechanisms and facilitate cellular conjugation has led to valuable insights into the mechanisms of cell function. A common feature of currently available cellular conjugation agents is their reliance on endogenous membrane molecules on both cell types as anchors for cellular interactions. In this report, we describe a method for incorporating palmitate-derivatized antibody molecules onto cell membranes where they function as 'surrogate receptors' (SR) for mediating specific cellular interactions. In this system, SR are attached to the plasma membrane by insertion of the palmitate hydrocarbon chains into the outer leaflet of the phospholipid bilayer. Therefore, the palmitate anchor bypasses the requirement for FcR or other endogenous membrane proteins in antibody-dependent cellular conjugation. Due to this mode of attachment, which is similar to that of phosphatidylinositol (PI) anchored proteins, SR-mediated cellular interactions are likely to be reminiscent of native receptor-induced conjugation, enabling SR to cooperate with endogenous target recognition structures in receptor-ligand interactions at the cell-cell interface.

Demonstration of pemphigus antibodies on the cell surface of murine epidermal cell monolayers and their internalization

The pathogenic effects of pemphigus vulgaris (PV) antibodies on epidermal cells can be demonstrated both in vitro using skin organ culture or primary epidermal cell cultures (PECC) and in vivo by passive transfer of PV antibodies into neonatal BALB/c mice. Although PV antibodies have been localized on the epidermal cell surface by several techniques, little is known about the fate of these autoantibodies subsequent to their surface binding. We have examined this, using murine PECC which express pemphigus antigen on their surface, and followed the fate of the bound antibody molecules. Forty-eight-hour PECC were incubated at 37 degrees C with PV antibodies for 20 min and then with horseradish peroxidase-labelled antihuman IgG. This was considered time 0. The monolayers were fixed with glutaraldehyde after 0, 0.5, 1, 3, 6, 18, and 24 h incubation at 37 degrees C and then processed for electron microscopy. At time 0 hour, PV antibodies is detected bound evenly along the surface of keratinocytes. Within 30 min, the bound PV antibodies becomes clustered, internalized into submembranous vesicles via surface pits, and eventually fused with lysosomes. Widening of the intercellular spaces was also seen in PECC treated with PV antibodies within the first 24 h. PECC treated with normal human IgG in parallel cultures showed no such surface binding, internalization, or cell-cell detachment. Treatment with cytochalasin-D and/or colchicine did not affect the internalization of the PV antibodies, but fusion with lysosomes was not seen in treated cultures. These findings suggest that PV antibodies binds a surface antigen and the complex is internalized and fused with lysosomes in a process that may have pathophysiologic relevance.

Pemphigoid and pemphigus antigens in cultured epidermal cells

Fractions of IgG from sera of patients with pemphigoid and pemphigus added to monolayer cultures of mouse epidermal cells resulted in a sparse distribution of cells. Direct immunofluorescence studies of these monolayers revealed epidermal cell surface antigens reacting with pemphigoid and pemphigus antibodies. We suggest that these antibodies may bind to epidermal cell surface antigenic molecules which are important in maintaining epidermal cell adhesion in culture.

Segmental response of the macrophage plasma membrane to a phagocytic stimulus

A method of attaching mouse RBCs to mouse macrophages is described. Both cell types were coated with rabbit anti-mouse macrophage F(ab')(2), and cross-linkage of cells was effected with sheep F(ab')(2) directed against rabbit F(ab')(2). 98% of macrophages attached an average of 11 RBCs each. Attachment occurred at 37 degrees C and was stable for at least 4 h. Less than 0.1% of macrophages ingested RBCs under these conditions. Latex particles and opsonized pneumococci were ingested as avidly by RBC-coated macrophages as by native macrophages. Ingestion of these particles did not prompt ingestion of attached RBCs. When anti-RBC IgG was added, however, over 90% of macrophages ingested an average of six RBCs each. Thus, ingestion of one particle does not trigger generalized phagocytosis of all particles attached to the cell's plasma membrane, and the phagocytic stimulus is confined to the segment of the cell's plasma membrane immediately adjacent to the particle being ingested.

Humoral immunostimulation. I. Increased uptake of (125I)iododeoxyuridine and (3H)thymidine into TNP-cells treated with anti-TNP antibody

Interaction of microgram quantities of highly purified rabbit anti-TNP antibodies with TNP-substituted HeLa, HEp-2, and L cells caused an intense stimulation of radioactive nucleoside ([(125)I]UdR and [(3)H]TdR) uptake which was maximal 24-72 h after exposure of cells to antibody. The stimulation of nucleoside uptake and presumaly DNA synthesis was shown to be immuno logically mediated because unsubstituted cells were not stimulated by anti-TNP antibody, normal rabbit gamma globulin did not stimulate TNP-cells, and a hapten inhibitor, epsilon-DNP-lysine, prevented the stimulation of TNP-cells by anti-TNP antibody. These findings demonstrate that interaction of antibody with cell surface antigen can alter cell membrane transport, and possibly can enhance cell growth.

Early events in cell-animal virus interactions

Images

The selective inhibition of macrophage phagocytic receptors by anti-membrane antibodies

Rabbit antibodies were prepared against purified mouse macrophages, erythrocytes, and liver lysosomes. In the presence of complement each of these reagents was capable of lysing mouse erythrocytes and macrophages. In the absence of complement, all antisera agglutinated mouse erythrocytes and at high concentration produced a cytotoxic effect on macrophages. At IgG concentrations of 100 microg/ml, no morphological evidence of cytotoxicity was evident. These data suggest the presence of common antigens on the erythrocyte and macrophage plasma membrane. Anti-macrophage, anti-erythrocyte, and anti-lysosomal gamma-globulins and IgG, employed at subtoxic concentrations, all inhibited the attachment and ingestion of opsonized erythrocytes and mycoplasma. This occurred without significant reduction in the phagocytosis of polystyrene particles, formalinized erythrocytes, and yeast cell walls. Each of the anti-membrane IgG antibodies was capable of blocking the Fc receptor on the macrophage plasma membrane. Attachment to the macrophage membrane occurred by means of the Fab region. However, a role for the Fc portion of the molecule was suggested since pepsin-digested IgG was unable to block the receptor. Each of the IgG antibodies produced a partial blockade of the complement receptor and reduced the ingestion of EAC1,4,2,3 by approximately 50%.

Primary antibody response in vitro in peritoneal cells

Peritoneal cells (PC), from nonimmunized mice, incubated in a carboxymethyl cellulose gum containing sheep red blood cells (SRBC) and guinea pig complement (following the technique of Ingraham and Bussard) start to produce plaques of hemolysis 20 hr after the beginning of incubation at 37 degrees C. In contrast, spleen cells from immunized mice complete their plaque-forming activity in 6 hr. The fact that formation of plaques by previously uncommitted cells is related to the life of the leukocytes, and is complement dependent brings evidence that we are dealing with an immunological phenomenon. Puromycin suppresses the formation of plaque. Previous incubation of the PC with SRBC in liquid medium, before incorporation in the detection system, reduces the lag in the production of plaques. This indicates that a phase of stimulation precedes the phase of expression (manifested by plaque formation). The immunological activity of the peritoneal cell suspension is highly dependent on the concentration of the suspension, which indicates that this activity results from a cooperative process. Actinomycin D, which does not suppress the production of plaques by cells from immunized animals, stops completely the in vitro induction. It is concluded that we have probably observed a primary immune response induced in vitro.