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Biomedical subjects

F Zavala

Publications and source records attributed to F Zavala.

At least 109 records · Page 6Linked to original sources
PubMed1985

Rationale for development of a synthetic vaccine against Plasmodium falciparum malaria.

Protective immunity against malaria can be obtained by vaccination with irradiated sporozoites. The protective antigens known as circumsporozoite (CS) proteins, are polypeptides that cover the surface membrane of the parasite. The CS proteins contain species-specific immunodominant epitopes formed by tandem repeated sequences of amino acids. Here it is shown that the dominant epitope of Plasmodium falciparum is contained in the synthetic dodecapeptide Asn-Ala-Asn-Pro-Asn-Ala-Asn-Pro-Asn-Ala-Pro or (NANP)3. Monoclonal antibodies and most or all polyclonal human antibodies to the sporozoites react with (NANP)3, and polyclonal antibodies raised against the synthetic peptide (NANP)3 react with the surface of the parasite and neutralize its infectivity. Since (NANP)3 repeats are present in CS proteins of P. falciparum from many parts of the world, this epitope is a logical target for vaccine development.

Adult↗
PubMed1985

Ubiquity of the repetitive epitope of the CS protein in different isolates of human malaria parasites.

Sporozoites of the human malaria Plasmodium falciparum and Plasmodium vivax obtained from a large number of endemic areas were screened with species-specific monoclonal antibodies that recognize the repeated epitopes of the respective circumsporozoite (CS) proteins. By using a two-site immunoradiometric assay, it was determined that all the parasite isolates of a given species react with a single monoclonal antibody, indicating the presence of a common repeated epitope. Polyacrylamide gel electrophoresis, followed by Western blot, showed that the CS proteins of the various isolates differed in their apparent m.w.

Animals↗
PubMed1985

Immunoradiometric assay to measure the in vitro penetration of sporozoites of malaria parasites into hepatoma cells.

We describe here an immunoradiometric assay to quantitate the in vitro invasion of hepatoma cells by sporozoites. The assay measures levels of circumsporozoite (CS) antigen that remain associated with the hepatoma cells after their incubation with the parasites. Several observations show that these measurements reflect internalized rather than extracellular antigen. For example, when incubations were performed with nonviable parasites (sonicated or heated), or in the presence of metabolic inhibitors, such as sodium azide and deoxyglucose, the amounts of CS antigen found in hepatoma cell extracts were greatly diminished. Moreover, Western blotting experiments revealed a striking difference in the pattern of CS proteins of infected cell extracts as compared with those of free parasites. The assay was used to measure the amounts of intracellular CS antigen for several days after infection of the hepatoma cells. The results confirmed previous microscopic observations, made by using immunofluorescence techniques, showing that the CS antigen in the host's liver cells diminishes progressively while the parasite develops into the exoerythrocytic stage. The immunoradiometric assay should facilitate the evaluation of the effects of drugs on sporozoites and also on studies aimed at the identification of a sporozoite receptor on the hepatocyte.

Animals↗
PubMed1985

[Presence of a peripheral type benzodiazepine binding site on the macrophage; its possible role in immunomodulation].

Saturable binding site for 3H-flunitrazepam (KD = 43 +/- 7 nM, Bmax = 391 +/- 58 fmoles/cell, i.e. 250,000 sites/cell) is characterized on Mouse peritoneal inflammatory macrophages. The affinity for different ligands (PK 11195 greater than Ro 5-4864 greater than diazepam greater than flunitrazepam greater than clonazepam greater than Ro 15-1788) shows that this site is of peripheral type. In vivo the humoral response in Mice to Sheep red blood cells was stimulated by administration of 1 mg/kg of PK 11195 (+85%), Ro 5-4864 (+80%) and diazepam (+58%). Clonazepam and Ro 15-1788 are devoid of activity. This suggests that molecules which show affinity for the "peripheral type" benzodiazepine binding site might modulate the immune response.

Animals↗
PubMed1984

Interaction of benzodiazepines with mouse macrophages.

Mouse peritoneal inflammatory macrophages have a saturable binding site for [3H]flunitrazepam with a KD of 43 +/- 7 nM and Bmax of 391 +/- 58 fmol per 10(6) cells, which corresponds to 250 000 sites per cell. The IC50 values for PK 11195, Ro 5-4864, diazepam, flunitrazepam, clonazepam, ethyl-beta carboline 3-carboxylate and Ro 15-1788 were 5.6, 6.5, 21, 40, 3 000, 12 000 and 80 000 nM respectively; gamma-aminobutyric acid did not displace [3H]flunitrazepam. These results indicate that the benzodiazepine binding site on the macrophage is of the peripheral type. In vivo experiments show that, at 1 mg/kg, peripheral and mixed type molecules stimulate the humoral response to sheep red blood cells while central type benzodiazepines are inactive. The hypothesis that this effect is mediated through the binding on the macrophage may be considered.

Animals↗
PubMed1984

DNA cloning of Plasmodium falciparum circumsporozoite gene: amino acid sequence of repetitive epitope.

A clone of complementary DNA encoding the circumsporozoite (CS) protein of the human malaria parasite Plasmodium falciparum has been isolated by screening an Escherichia coli complementary DNA library with a monoclonal antibody to the CS protein. The DNA sequence of the complementary DNA insert encodes a four-amino acid sequence: proline-asparagine-alanine-asparagine, tandemly repeated 23 times. The CS beta-lactamase fusion protein specifically binds monoclonal antibodies to the CS protein and inhibits the binding of these antibodies to native Plasmodium falciparum CS protein. These findings provide a basis for the development of a vaccine against Plasmodium falciparum malaria.

Amino Acid Sequence↗
PubMed1984

Identification of malaria-infected mosquitoes by a two-site enzyme-linked immunosorbent assay.

A micro enzyme-linked immunosorbent assay (ELISA) for identifying malaria sporozoites in mosquitoes is described. Using an extract of dried infected mosquitoes as antigen, a two-site ELISA was sensitive enough to detect one infected mosquito in a pool of 20. The species specificity, sensitivity and ease of performance of this assay, as well as the stability of the reagent, should make it a useful epidemiological tool.

Animals↗
PubMed1984

First field trial of an immunoradiometric assay for the detection of malaria sporozoites in mosquitoes.

An immunoradiometric assay (IRMA) using a monoclonal antibody to the major surface protein of Plasmodium falciparum sporozoites was used to assess the P. falciparum sporozoite rate in a West African population of Anopheles gambiae (s.1.). Unlike current dissection techniques, the IRMA could detect sporozoite antigen in dried as well as fresh mosquitoes. In a controlled comparison, the sensitivity of the IRMA was comparable that of the dissection technique. Additionally, the IRMA was species specific and quantitative. Sensitivity of the assay was sufficient to detect sporozoite infections resulting from the development of a single oocyst.

Animals↗
PubMed1983

Circumsporozoite proteins of malaria parasites contain a single immunodominant region with two or more identical epitopes.

We have used panels of monoclonal antibodies to circumsporozoite (CS) proteins of Plasmodium falciparium, P. vivax, and P. knowlesi to determine the number of topographically independent epitopes of these antigens. The results of competition binding assays indicated that single regions of the CS molecules were recognized by the homologous monoclonal antibodies. Competition binding assays were also used to study the specificity of antibodies contained in the sera of humans and monkeys that had developed sterile immunity after immunization with irradiated, intact sporozoites. We found that single monoclonal antibodies inhibited 70-95% of the specific binding of the polyclonal antibodies to crude extracts of sporozoites. It appears, therefore, that CS proteins are among the most immunogenic constituents of sporozoites, and that a single region of these molecules contains most of the immunogenic activity. An additional finding was that the immunodominant region of CS molecules is multivalent with regard to the expression of a single epitope. This was demonstrated by the ability of monomers of CS proteins to bind simultaneously two or more molecules of the same monoclonal antibody.

Animals↗
PubMed1982

Inhibition of idiotype--anti-idiotype interaction for detection of a parasite antigen: a new immunoassay.

Described in this report is an immunoradiometric assay of general applicability that is based on a new principle: the inhibition of the interaction between monoclonal antibodies by an antigen. The advantages of this assay are that it measures concentrations of single epitopes, purified antigen is not required, and the reagents can be obtained in unlimited amounts and are homogeneous. Its features are particularly attractive when the antigen has not been purified and is a minor component of a complex mixture of molecule.

Animals↗
PubMed1980

Structure--antitubulin activity relationship in steganacin congeners and analogues. Inhibition of tubulin polymerization in vitro by (+/-)-isodeoxypodophyllotoxin.

A new series of 23 synthetic analogues of the naturally occurring antitumor lignan steganacin was tested for the inhibition of microtubule assembly in vitro. Interestingly, (+/-)-isopicrostegane (I50 = 5 microM) was found to be almost as active as (+/-)-steganacin(I50 = 3.5 microM). On the other hand, racemic isodeoxypodophyllotoxin has an inhibiting activity of microtubule assembly comparable to that of (-)-podophyllotoxin, whereas (-)-isodeoxypodophyllotoxin is totally inactive.

Colchicine↗
PubMed1979

Immune response to glutaraldehyde-treated cells. I. Dissociation of immunological memory and antibody production.

Glutaraldehyde (GA)-treated sheep red blood cells (SRBC) or H-2-allogeneic spleen cells (SC), induced immunological memory with absent or markedly reduced primary antibody production. In contrast, a normal secondary response was obtained when GA-SRBC or GA-SC were given to mice primed with the corresponding untreated antigens. The secondary response of mice primed and boosted with GA-treated cells was relatively high with GA-SRBC, and negative or very low with GA-SC. Morphological studies of the fate of intraperitoneally injected cells showed that endocytosed GA-SRBC persisted much longer in peritoneal macrophages than untreated SRBC. Simultaneous challenge of mice with untreated and GA-treated SRBC revealed that phagocytosis and digestion of both types of cells in the same macrophage proceeded independently of each other. The primary response of mice receiving both SRBC and GA-SRBC was entirely similar to the response when SRBC alone was given.

Aldehydes↗