Studies on Limulus amoebocyte. Isolation and identification of a membrane-bound protein activator of cyclic nucleotide phosphodiesterase from Limulus amoebocyte

The limulus clotting reaction

Our biochemical studies on the hemolymph coagulation-complement system using limulus indicate that the circulating hemocytes contain at least four serine protease zymogens and one clottable protein, coagulogen, which constitute a cascade triggered by bacterial endotoxins and (1,3)-beta-D-glucan. We also found several antimicrobial substances, tachyplesin peptides and anti-lipopolysaccharide factor, in the hemocytes. These clotting factors and antimicrobial substances are released into the hemolymph in response to lipopolysaccharide, where they cooperate in immobilization and killing of invading microorganisms as a host defense.

Demonstration of soluble Plasmodium falciparum antigens reactive with Limulus amoebocyte lysate and polymyxin B

To investigate whether soluble Plasmodium falciparum antigens possess endotoxin-like properties, the interaction of Limulus amoebocyte lysate (LAL) with defined soluble antigens from Plasmodium falciparum was studied by various crossed immunoelectrophoretic methods and immunoblotting. The soluble P. falciparum antigens were purified by affinity chromatography using human IgG from malaria-immune adults as ligand. Of eight possible antigens, at least three were affected by LAL, as indicated by disappearance of these antigens in the precipitation pattern, after the reaction with LAL. One of the LAL-reactive antigens is a heat-stable glycoprotein with the presence of both hydrophilic and hydrophobic regions in its structure. This antigen shows a strong reaction with polymyxin B, and antibodies against it have been shown to be inhibitory to the growth of P. falciparum in culture. It is concluded that LAL reacts with several soluble antigens from P. falciparum and it is suggested that these antigens participate in the induction of protective immunity to malaria, and consequently that one or more of the soluble antigens are candidates for a malaria vaccine.

Interaction between limulus amoebocyte lysate and soluble antigens from Pseudomonas aeruginosa and Staphylococcus aureus studied by quantitative immunoelectrophoresis

To investigate the interaction of Limulus amoebocyte lysate (LAL) with gram-negative bacteria, soluble antigens from sonicated Pseudomonas aeruginosa were studied by various crossed-immunoelectrophoresis methods before and after reaction with LAL. Of 64 possible, at least 7 antigens were affected, as indicated by precipitin pattern, after the reaction with LAL. The precipitates corresponding to lipopolysaccharide and Pseudomonas "common antigen" disappeared. This reaction was inhibited when LAL was pretreated with lipopolysaccharide or by heating. Several of the reacting antigens have been shown to cross-react with many other strains of both gram-negative and gram-positive bacteria. Soluble antigens from a protein A-deficient strain of Staphylococcus aureus were also studied. LAL reacted with at least four of these antigens, including the teichoic acid complex. It is concluded that LAL is highly reactive with lipopolysaccharide, but it can react with other antigens from gram-negative and gram-positive bacteria as well. It is suggested that LAL interacts with biologically important antigens from the bacterial membrane. It is proposed that the reactivity and specificity of LAL for various microbial antigens can be studied by immunoelectrophoretic techniques.

African trypanosomes contain calmodulin which is distinct from host calmodulin

Studies were initiated to determine whether African trypanosomes utilize Ca2+ fluxes to coordinate complex morphological and biochemical life cycle changes. We have identified the ubiquitous intracellular Ca2+ receptor, calmodulin, in two developmental stages of Trypanosoma brucei rhodesiense. The transition from rapidly dividing, slender bloodstream trypomastigotes to slow growing procyclics in axenic culture was accompanied by changes in specific calmodulin content (3 micrograms/mg cell protein to 1 microgram/mg cell protein, respectively) and a shift in intracellular calmodulin distribution, Trypanosome calmodulin is physically and functionally distinct from that of host tissues, including bovine brain and rat erythrocytes. It is similar to but distinct from Tetrahymena calmodulin. Comparisons among these proteins isolated from the four sources were made using the following criteria: (1) mobility on sodium dodecyl sulfate discontinuous polyacrylamide gels; (2) Ca2+-induced conformational changes; (3) CNBr-cleavage fragments; (4) activation of bovine brain cyclic nucleotide phosphodiesterase in both a Ca2+-dependent and calmodulin-dependent manner; (5) activation of human erythrocyte (Ca2+ + Mg2+)-ATPase; and (6) inhibition of calmodulin activity by trifluoperazine and penfluridol. Trifluoperazine but not trifluoperazine sulfoxide was cytotoxic to trypanosomes in vitro. Half maximal effect occurred at 15 microM. We conclude that calmodulin is a functional component of Africal trypanosomes and suggest that it plays an important role in mediating the host-parasite relationship.