Further characterization of cooperative interactions of monoclonal antibodies

We reported previously that mixtures of some monoclonal antibodies directed against the glycoprotein hormone human chorionic gonadotropin (hCG) had a higher affinity for the antigen than either monoclonal antibody separately. The synergistic interaction could no longer be detected when one of the antibodies was replaced with its F(ab) fragment. This cooperative interaction has now been further characterized. One-half of 10 possible pairs prepared from five IgG1 monoclonal antibodies against hCG result in a synergistic interaction. The addition of an IgG2b monoclonal antibody to one of the IgG1 monoclonal antibodies also induces a cooperative interaction, which shows that the effect is not subclass restricted. Cooperative interactions between antibodies are also not restricted to solution conditions; adsorption of one antibody to a solid support appears to increase the cooperative effect. Indeed, one pair of antibodies that failed to bind hCG synergistically in solution did so when one antibody was bound to a solid surface. The liquid phase antibody also has an effect on the specificity of the solid phase antibody. The sensitivity of the solid phase assay system has enabled us to develop a rapid method of determining if two monoclonal antibodies can bind to an antigen simultaneously. A quantitative theoretical model has been devised that successfully predicts the cooperative behavior observed between antibodies and should be useful in devising conditions that result in sensitive solid phase radioimmunoassays.     

Haemolysis of rabbit erythrocytes by a lectin from the seeds of<Emphasis Type="Italic">Croton tiglium</Emphasis>

The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K⁺, Ca²⁺ and Mg²⁺ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).     

“Pleiotypic Response”

A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.