Asher Frensdorff

Membrane mobility agents. A new class of biologically active molecules

Abstract A number of cyclopropane fatty acid esters which promote the lateral mobility of fluorescent antibody-labeled antigenic sites through lymphocyte membranes (measured by rate and extent of cap formation) are described. The effect is dependent on molecular structure and dose; the compounds are termed membrane mobility agents.

Proteins from the liehenXanthoria parietina which bind to phycobiont cell walls Localization in the intact liehen and cultured mycobiont

SummaryA protein fraction, previously isolated from the lichenXanthoria parietina and known to bind to the appropriate culturedTrebouxia phycobiont, was visualized in the intact lichen thallus and cultured mycobiont by an indirect immunoperoxidase assay. The protein was localized in both the upper and lower cortices of the lichen thallus; it was also present in the cell walls of the mycobiont culturedin vitro. The possible role of this protein in the recognition, or initial interaction, between separated lichen symbionts is discussed.

Selectivity in the Lichen Symbiosis

The terms specificity and selectivity, which have been used to describe distinct types of cellular behaviour during cell-cell adhesion between animal cells (Garrod and Nicol, 1981), will be used here to describe cellular interactions between symbionts. In our view, specificity describes an interaction in which absolute exclusiveness is expressed; two types of bionts associate only with one another and no other potential combinations between them are observed. In contrast, selectivity describes a situation where bionts interact preferentially with one another. If a host (or vice versa) is presented with a choice of bionts, it will preferentially associate with one over the others.

Isolation of lymphocyte subpopulations from rabbit peripheral blood. comparison of methods based on recovery of rosette-forming cells and on recovery of Ig-bearing cells from a digestible immunoadsorbent☆

Two methods to obtain lymphocyte subpopulations, defined by specific surface receptors, from rabbit peripheral blood cells were compared as to cell recovery, yield and purity of the obtained fractions: a) the formation of rosettes between lymphocytes and SRBC or SRBC coated with an antigen--antibody--complement complex (D-SRBC), followed by isolation of the rosettes and recovery of the RFC, b) retention of surface-Ig bearing cells on an immunoadsorbent to which antibody to rabbit Ig was covalently attached via a digestible gelatin bridge, with subsequent recovery of the retained cells by the enzymatic digestion of the bridge. Purity of the isolated cell fractions was assessed in all cases by the percentage of cells staining with FITC-labeled goat anti-rabbit Ig. Using the rosette method, all of the RFC could be recovered from rosettes and a very pure, surface-Ig negative, sub-population of cells was obtained: however, the overall number of rosettes formed (SRBC and D-SRBC) was low (8-9% of the nucleated PBC). Very good recoveries and highly enriched cell populations were obtained with the digestible immunoadsorbent, provided certain precautions to minimize cell losses were taken. Thus, 47% of the input cells, representing 90% of the lymphocytes could be recovered; separated cell populations were 96% Ig-positive or, in another experiment, 96% Ig-negative.

Relationship between unicellular cyanobacteria established by indirect immunofluorescence of intact cells

Antisera prepared against intact, viable cells were used to show the applicability of a serological approach to detect relationships between unicellular cyanobacteria. Antisera were raised against eight unicellular cyanobacteria and two chlorophycean unicellular organisms. The staining reactivity of each antiserum was tested by the fixed indirect immunofluorescence assay against the different organisms, and each organism was tested for its reactivity with all of the different antisera. Absorption of antisera with the appropriate heterologous antigens was used to further characterize the relationship betweenAnacystis nidulans andSynechococcus cedrorum, and also the relationship between two subcultures of an isolate distinguished by morphological features. Absorption of antiserum was also used for the removal of antibodies to contaminating bacteria. The approaches used are suggested as a useful tool for determining relationships between unicellular cyanobacteria.

Immobilized whole algal cells for solid-phase binding assays

Abstract Whole algal cell, phycobionts from Xanthoria parietina, Caloplaca citrina and Ramalina pollinaria, were immobilized onto the surface of wells of PVC microtiter plates. Two approaches were investigated: (a) immobilization via adsorption through ionic forces, viz., adsorption on polylysine-coated or cationized BSA-coated surfaces and (b) immobilization via covalent binding of cells onto chemically reactive surfaces obtained by coating the latter with BSA followed by activation with glutaraldehyde. To test the suitability of these systems for solid-phase binding assays, the immobilized cells were exposed to antisera against whole algal cells; bound antiserum was quantitated by the addition of 125I-PrA and counting. Non-specific binding of immunoglobulins to the modified PVC surfaces and the immobilized cells was efficiently blocked with normal goat serum. Of the systems studied, cells immobilized onto PVC microtiter wells, by either covalent binding or by electrostatic absorption to cationized BSA-coated surfaces, were found to be most suitable for solid-phase binding assays.

Effect of Vinblastine on the Early Events in the Humoral Immune Response of Mice to SRBC

The effect of vinblastine (VLB), a mitotic blocking agent, on the number of plaque-forming cells (PFC) and on the metabolic activities of spleen cells of mice reimmunized with SRBC was studied. When VLB (75 mug/mouse) and antigen were administered simultaneously, the number of pfc, on the 4th day after immunization, was reduced to 40% of control levels. However, when the same amount of VLB was administered to mice 24 h after immunization, it reduced the number of PFC to 10% of control levels. The possibility that VLB exerts a specific cytotoxic effect on preformed PFC either in vivo or in vitro was ruled out. A direct profound effect of VLB on antigen-stimulated cells was observed when VLB was injected 24 h after reimmunization, and the incorporation rates of radioactive precursors into macromolecules by spleen cells were measured at 4-hour intervals. VLB suppressed completely the antigen-induced peak of 3H-thymiding incorporation, while it had no effect on the incorporation rate of 3H-uridine and only a slight effect on the incorporation rate of 3H-amino-acids by the same cells. The results suggest that the decrease in number of PFC caused by injection of VLB 24 h after immunization is due to prevention by VLB, of precursor cells from going through a critical cell division, which takes place later than 24 h after immunization. Thus, at least one cell division is required for an immune response in vivo.

The presence of cells expressing immune-complex receptors in non-lymphoid murine tumors.

In this study we demonstrated that cells lodging in tumors have the capacity to fix antibody or immune complexes in vivo and in vitro. Although some of the fixation is probably by host, at least in one system studied, tumor cells, per se, were found to exhibit immune complex fixation.