Leishmanial excreted factor: protein-bound and free forms from promastigote cultures of Leishmania tropica and Leishmania donovani

Characterization of phosphoglycan-containing secretory products of Leishmania

This article presents an overview on phosphoglycan-containing components secreted by the insect and mammalian stages of several species of Leishmania, the causative agents of leishmaniasis in the Old and New World. Firstly, promastigotes of all three species considered, L. mexicana, L. donovani and L. major, shed lipophosphoglycan (LPG) into the culture medium possibly by release of micelles from the cell surface. Like the cell-associated LPG, culture supernatant LPG is amphiphilic and composed of a lysoalkylphosphatidylinositol-phosphosaccharide core connected to species-specific phosphosaccharide repeats and oligosaccharide caps. Secondly, all three species release hydrophilic phosphoglycan. Thirdly, all three species appear to secrete proteins covalently modified by phosphosaccharide repeats and oligosaccharide caps. In the case of promastigotes of L. mexicana, these components are organized as two filamentous polymers released from the flagellar pocket: the secreted acid phosphatase (sAP) composed of a 100 kDa phosphoglycoprotein and a protein-containing high-molecular-weight-phosphoglycan (proteo-HMWPG) and fibrous networks likewise composed of phosphoglycan possibly linked to protein. Structural analyses and gene cloning suggest that the parasites can covalently modify protein regions rich in serine and threonine residues by the attachment of phosphosaccharide repeats capped by oligosaccharides. We propose that the networks formed in vitro correspond to fibrous material previously demonstrated in the digestive tract of infected sandflies. In the case of L. donovani, the sAP is also modified by phosphoglycans but contains neither proteo-HMWPG nor does it aggregate to filaments. Finally, L. mexicana amastigotes release proteo-HMWPG via the flagellar pocket into the parasitophorous vacuole of infected macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of the human phagocyte oxidative responses caused by Leishmania lipophosphoglycan (LPG): in vitro studies

Lipophosphoglycan (LPG), a surface glycoconjugate of Leishmania promastigotes, has been reported as playing an active role in protecting the parasite within phagolysosomes, by an impairment of monocyte oxidative responses. In this study the effect of LPG on the oxidative burst of human peripheral monocytes, eosinophils and neutrophils was evaluated. Our results demonstrated that either superoxide anion (O2-) or hydrogen peroxide (H2O2) release by LPG-pretreated cells was diminished, emphasizing the ability of this glycoconjugate to impair the oxidative activity of all phagocytes.

Monoclonal antibodies directed against Leishmania secreted acid phosphatase and lipophosphoglycan. Partial characterization of private and public epitopes

Leishmania promastigotes, the stage of the parasite characteristic for the sandfly vector, express an abundant glycoconjugate, called lipophosphoglycan, at their surface. Lipophosphoglycan consists of lysoalkyl-sn-glycerophosphoinositol linked to a phosphosaccharide core conserved in all species, which is connected to PO4-6Gal beta 1,4Man alpha 1 repeats with species-specific substitutions at the Gal residue; the repeats are capped by conserved and species-specific oligosaccharides. Most Leishmania species also secrete an acid phosphatase, which, in Leishmania mexicana, is a filamentous complex composed of a phosphorylated glycoprotein and non-covalently associated proteo-(high-molecular-mass)phosphoglycan. The secreted acid phosphatase complex was used as an antigen to derive a panel of monoclonal antibodies (mAbs). A total of 25 mAbs (17 novel and 8 previously described) were tested by different techniques for their specificity against lipophosphoglycan and secreted acid phosphatase from several Leishmania species. This comparison and the modification of the antigens by chemical or enzymic treatments allowed a classification of the mAbs into several groups. First, from 25 mAbs examined, 22 recognize lipophosphoglycan and the enzyme complex of L. mexicana; only three are specific for secreted acid phosphatase. Two of the latter group are also directed against carbohydrate structures, whereas the third mAb recognizes the 100-kDa polypeptide of the complex. The secreted acid-phosphatase-specific class detects antigen in the flagellar pocket of promastigotes while all anti-lipophosphoglycan mAbs bind to the cell surface. Second, all 15 anti-lipophosphoglycan mAbs investigated in detail appear to be directed against the phosphosaccharide repeats or the cap structure rather than the phosphosaccharide core. Two mAbs recognize terminal cap-structures containing Man alpha 1,2Man residues. Four antibodies are specific for L. mexicana and are probably directed against PO4-6[Glc beta 1,3]Gal beta 1,4Man alpha 1 repeats while six mAbs react with the unmodified repeats. Two antibodies specific for Leishmania major recognize Gal beta 1,3-substituted repeats unique for lipophosphoglycan from this species. Analysis by immunoblotting indicates that the high-molecular-mass proteo-phosphoglycan of L. mexicana secreted acid phosphatase carries epitopes for all anti-lipophosphoglycan mAbs suggesting the presence of capped phosphosaccharide repeats while the enzymically active glycoprotein subunit is modified by caps but probably not by repeats. In the case of Leishmania donovani secreted acid phosphatase, the enzymically active polypeptide may be directly modified by repeats. The mAbs are used to characterize changes in lipophosphoglycan structure, which occur in culture during the transition of promastigotes from the logarithmic to the stationary growth phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical and immunological characterization of exometabolites from an Indian strain of Leishmania donovani promastigotes grown in a chemically defined medium

Exometabolites (EXOM) of an Indian strain of Leishmania donovani promastigotes isolated from a chemically defined medium by ultrafiltration consisted of proteins, glycoproteins, lipid and lipophosphopolysaccharide (LPPS). LPPS of Mr 40-28 kDa in SDS-PAGE could be labelled metabolically with [32P]-phosphate and recovered in the aqueous phase of hot-phenol-water extraction of EXOM (PE-Aq) along with a glycoprotein of Mr 150-130 kDa (GP150-130). These two molecules could be eluted from DE-52 column with 200 mM NaCl (D2). The 300 mM NaCl (D3) and 400 mM NaCl (D4) eluates from DE-52 column contained one unsaturated polar lipid component. The LPPS had Rf value of 0.65-0.75 in Thin Layer Chromatography (TLC) using saturated phenol water solvent system. EXOM revealed 15 bands in SDS-PAGE of which proteins of Mr 84, 66, 56, 50 and 29 kDa were prominent. When EXOM were fractionated through Con A-Sepharose column, the fraction eluted with alpha-methyl-D-mannoside (Con A-E) had seven bands as revealed by SDS-PAGE of which 25, 16, 13 and 12 kDa glycoproteins were prominent. The antigens present in EXOM can be classified as slower anodic migrating and faster anodic migrating antigens as revealed by immunoelectrophoresis (IEP). The slower anodic migrating antigens, LPPS and GP150-130 recovered in PE-Aq and D2 did not cross-react with kala-azar patients' sera but cross-reacted with homologous anti-promastigote sera. Two faster anodic migrating antigens which could be recovered in organic phase of hot phenol extraction of EXOM (PE-O) and eluted in D3 and D4 and Con A-E, cross-reacted with kala-azar patients' sera. The antigens of both the classes were sensitive to periodic acid oxidation.

Released glycoconjugate of indigenous Leishmania major enhances survival of a foreign L. major in Phlebotomus papatasi

The effect of Leishmania glycoconjugate in the vector was investigated using Phlebotomus papatasi artificially infected with a Leishmania major strain that this vector does not transmit in nature. Glycoconjugate of the vector-specific strain of L. major was added to the infective meals of some fly groups and the success of infections with or without this substance was compared 4 d later. In the absence of glycoconjugate the parasites survived in 15.6% of the flies, while the addition of 0.5 mg/ml and 2 mg/ml raised the rate of infection to 34.3% and 63.0% respectively. Undigested blood was found in the stomach of 7.8% of the infected flies, whereas following meals with parasites and 2 mg/ml glycoconjugate it was present in 37% of the flies. The results demonstrated that this glycoconjugate increased the viability of the parasites in the unsuitable vector and delayed digestion of the infective meals. In a parallel experiment the glycoconjugate of L. donovani did not affect the survival of the parasites.

Leishmania tropica: characterization of a lipophosphoglycan-like antigen recognized by species-specific monoclonal antibodies

Species-specific monoclonal antibodies to Leishmania tropica, T11 and T13-15, recognize membranal and secreted antigens. The membrane form of the antigen migrates on sodium dodecyl sulfate-polyacrylamide gels with a diffuse molecular weight from 15 to 50 kDa and can be labeled with palmitic acid, myoinositol, galactose, glucosamine, and inorganic phosphate. Both phosphate and sugar-labeled material were isolated from metabolically labeled promastigotes by affinity chromatography on antibodies coupled to Sepharose 4B. No binding to Ricinus communis agglutinin was observed. This material behaves like lipophosphoglycans from other Leishmania but contains unique species-specific epitopes. It is susceptible to cleavage by phospholipase C and after digestion no longer partitions into the detergent phase following a Triton X-114 extraction. All four monoclonal antibodies appear to recognize a carbohydrate epitope on the lipophosphoglycan since periodate treatment of this material bound to nitrocellulose essentially eliminated antibody binding. In addition, T15 binding could be blocked by 5 mM mannose-6-PO4 and fructose-1- or 6-PO4, but not by mannose, glucose, fructose, or the additional PO4 derivatives examined. The antibodies recognize a similar but not identical epitope, as demonstrated by a competitive radioimmunoassay using 125I-labeled T11, T13, and T15. Expression of surface antigen is elevated during the promastigote stationary phase.

Inhibitory effects on protein kinase C activity by lipophosphoglycan fragments and glycosylphosphatidylinositol antigens of the protozoan parasite Leishmania

Fragments of the lipophosphoglycan of Leishmania donovani were generated by phospholipase C digestion and mild acid hydrolysis. The fragments were purified and examined for inhibitory activity on protein kinase C isolated from rat brains. On a molar basis, the 1-O-alkylglycerol portion of LPG exhibited the most inhibitory activity, whereas the carbohydrate domain was not as effective. In addition, several glycolipid antigens from L. major, which contain short carbohydrate chains attached to phosphatidylinositol, were also efficient inhibitors of the enzyme. These results are consistent with the hypothesis that protein kinase C may be a key target for the parasites to overcome within host macrophages.

Leishmania donovani: identification of glycoproteins released by promastigotes during growth in vitro

Culture supernatants of metabolically labeled Leishmania donovani promastigotes were shown to contain approximately 40 electrophoretically distinct released protein compounds. Of these, approximately 20 were glycoproteins which contained terminal mannose residues, as judged by their specific binding to concanavalin A-agarose beads. Smaller subsets of the released glycoproteins were bound by agarose-conjugated Lens culinaris, Ricinus communis, and peanut lectins. Promastigote mannose-containing released glycoproteins were isolated by concanavalin A affinity chromatography and used to immunize a rabbit. This antiserum recognized the parasite-released mannose-containing glycoproteins, including the soluble acid phosphatase, both by immunoprecipitation from solution and in immunoblot analyses. In an antibody bridged enzyme assay this polyspecific serum was also capable of binding native acid phosphatase out of solution and bridging it to the denatured enzyme on SDS-PAGE transblots. Although this antiserum was raised against all 20 released glycoproteins, in agarose gels its major precipitin activity was against the secreted soluble acid phosphatase.

The lipophosphoglycan of Leishmania

The major cell surface glycoconjugate of leishmanial parasites is lipophosphoglycan (LPG). Its relative abundance, unique structure, and cellular location suggest one or more important roles in interactions between parasites and host cells. In this article, Sam Turco examines current information about this novel glycoconjugate and its significance.

The macrophage-attachment glycoprotein gp63 is the predominant C3-acceptor site on Leishmania mexicana promastigotes

The interaction between Leishmania promastigotes and their vertebrate host's complement system results not only in parasite lysis but also, due to surface-bound complement components, in increased macrophage binding potential. In this study we demonstrate, with the use of isolated complement components, that activation is via the alternative complement pathway, initiated by direct deposition of C3 onto the parasite surface. The predominant C3 acceptor site on the promastigotes was initially identified as the glycoprotein gp63 by anti-C3 antibody immunoprecipitation of radioiodinated promastigotes following incubation in the alternative pathway initiators C3, and factors B and D. The C3-binding properties of gp63 were confirmed and quantified, in relation to other surface antigens, by incubating parasites in iodinated C3 and immunoprecipitating bound C3 with antibodies directed against different promastigote surface antigens. The other abundant surface antigen, the glycolipid 'excreted factor', did not show any C3-binding activity. Further demonstration was provided by incubating liposomes containing either gp63 or excreted factor in iodinated C3 and factors B and D. Only gp63-containing liposomes bound C3. Considering that both gp63 and the excreted factor have recently been implicated in attachment and uptake by macrophage, these findings may have considerable bearing in the determination of which of the macrophage surface receptors identify which parasite ligand.

Effect of tunicamycin on the extracellular acid phosphatase of Leishmania donovani promastigotes

Inhibition of replication of Leishmania donovani promastigotes in axenic culture medium by tunicamycin, an inhibitor of asparagine linked protein glycosylation, depends upon the cell density of the culture at the time of addition of tunicamycin as well as upon the concentration of tunicamycin itself. Parasite multiplication in cultures with initial densities of less than or equal to 1 X 10(6) cells ml-1 and a tunicamycin concentration of 1 microgram ml-1 was limited to 2-3 replications, but this limitation was not observed in cultures with initial densities greater than or equal to 2 X 10(6) cells ml-1. Under conditions in which tunicamycin inhibited parasite growth and protein synthesis by only 15% and 6%, respectively, there was a greater than 90% reduction in the level of secreted acid phosphatase activity in comparison to control cultures. The extracellular acid phosphatase activity remaining in tunicamycin treated cultures was electrophoretically distinct from that found in control cultures. No significant decrease in the amount of [35S]methionine incorporated into acid insoluble products in the supernatant of tunicamycin treated cultures was observed, and a radiolabeled protein with an electrophoretic Mr of 97,000 was immunoprecipitated from this supernatant by an anti extracellular acid phosphatase antiserum. It was concluded that the L. donovani extracellular acid phosphatase, previously shown to be a mannose containing glycoprotein, contains N-linked oligosaccharides which are necessary for maintenance of its catalytic activity, but not its secretion.

The effect of tunicamycin on Leishmania brasiliensis. Glycosylation and the cell surface components

Culture conditions of Leishmania cells were developed to allow the study of the effect of tunicamycin (TM) on glycosylation and on the cell surface components. Leishmania incorporate [14C]-mannose and [35S]-methionine in vitro. The incorporation of [14C]-mannose is linear for 150 min and is inhibited by TM (2 micrograms/ml) in a time dependent effect which reaches a plateau of 45% inhibition at 36 h. Under the same experimental conditions [35S]-methionine incorporation into protein is slightly affected. This is reflected by an almost identical polypeptide pattern for TM treated and non-treated cells when analyzed on SDS-PAGE. On the contrary, strong differences were detected on the labeled compounds analyzed on SDS-PAGE followed by autoradiography when the precursor used was [14C]-mannose. A shift in the electrophoretic mobility of most of the glycopeptides synthesized in the presence of TM was observed, which is also reflected in the structure of the main Leishmania cell surface components. The findings are discussed in the light of biological implications.

An amphipathic sulphated glycoconjugate of Leishmania: characterization with monoclonal antibodies

A major glycoconjugate of Leishmania tropica major identified by two monoclonal antibodies was shown to be an externally oriented, amphipathic membrane antigen shed into the culture medium in which the parasites grow. This molecule could be labelled metabolically with [3H]glucose, [3H]galactose, [32P]phosphate and [35S]sulphate. It migrated as a polydisperse band upon electrophoresis in SDS-polyacrylamide gels, spanning the region of the gel corresponding to an apparent mol. wt. of 20 000-67 000 daltons. An apparently identical family of molecules could be labelled on the surface of living promastigotes using galactose oxidase and [3H]-sodium borohydride. This molecule was shown to be released into the supernatant over a period of several hours. Detection of the 3H- or 35S-labelled molecule required several days exposure of autoradiographs, but a novel blotting technique using nitrocellulose coated with monoclonal antibody allowed rapid detection of the molecule in charge shift electrophoresis, Western blotting and dot blotting. The electrophoretic mobility of the glycoconjugate in agarose relative to its mobility in Triton X-100 was increased in the presence of deoxycholate, and decreased in the presence of cetyl trimethyl-ammonium bromide, indicating amphipathic properties consistent with insertion into the lipid bilayer of the membrane. Using the dot-blotting technique the glycoconjugate was detected in all virulent and avirulent clones of LRC-L137 and in two additional isolates of L. tropica major (LRC-L287 and LRC-L251), but not in L. donovani or L. mexicana, consistent with the previously described specificity of the antibodies. However, the general approaches used in this paper showed that L. donovani (LRC-L52) and L. mexicana (LRC-L94) synthesize a similar, but antigenically distinct glycoconjugate.

Monoclonal antibodies for serotyping Leishmania strains

Mouse monoclonal antibodies raised against Leishmania tropica major were found to precipitate with the excreted factor produced by this and other leishmanial species. We suggest that a classification system for Leishmania, based on selective precipitation reactions between monoclonal antibodies and the excreted factor, would remove many ambiguities that currently exist.

Action of leishmanial excreted factor (EF) on human lymphocyte blast transformation

The effect of Leishmania tropica major excreted factor (EF) on human immune and normal mononuclear peripheral blood cells has been studied. The response of lymphocytes to stimulation either specifically with leishmanial antigens or non-specifically with phytohemagglutinin (PHA) in the presence of EF was tested by the uptake of 3 [H]thymidine. The results showed that EF inhibits the response of cells from immune donors to leishmanial antigens and from normal donors to PHA or PPD. Adherent and non-adherent cells were separated and the effect of EF on both populations was analysed. The results showed that EF inhibited blast transformation if both EF and antigen were presented to each of the separate populations. The inhibition of the adherent cells (mainly monocytes) was more marked than the inhibition of the non-adherent population (mainly lymphocytes).

Leishmanial excreted factors (EFs): purification by affinity chromatography

Leishmania species grown in culture excrete a polyanionic, carbohydrate-rich factor (EF) which binds to antibodies produced in rabbits against the parent Leishmania species. EF, previously purified by physical and chemical methods, was purified by affinity chromatography on a Ricinus lectin column. The purified samples were characterised and analysed. The results show a notable proportion of galactose in EF and clarify the reasons for its polyanionic properties. Heterogenicity of EF is demonstrated and discussed.

Cell-mediated killing of protozoa

Cell-mediated immunity represents an important host defence mechanism against protozoal infections. The effector cells directly involved are neutrophils, macrophages and, ultimately, activated macrophages. Within this simple scheme there are, however, considerable variations in activity. Effector cells from different animal species, and even from different strains of the same species, may be more or less effective in controlling a certain protozoal infection. Different protozoa differ in their susceptibility to cell-mediated killing according to genus, species, strain and morphological form. The most susceptible morphological form is that which occurs in the insect vector, and which has not yet adapted to protect itself from the vertebrate host. Epimastigotes of Trypanosoma and promastigotes of Leishmania are readily killed by phagocytic cells, while the corresponding trypomastigote and amastigote forms are considerably more resistant. Protozoa which live in macrophages, such as amastigotes of Leishmania, endozoites (tachyzoites) of Toxoplasma and amastigotes of reticulotropic strains of T. cruzi, have developed a remarkable resistance to the microbicidal activity of the host cell. Conversely, amastigotes of myotropic strains of T. cruzi, which live in muscle cells, have not developed this resistance to cell-mediated killing by macrophages. Readily accessible protozoa, such as T. brucei trypomastigotes and Plasmodium merozoites in the bloodstream, while they lack the marked resistance developed by reticulotropic protozoa, have a partial protection since they are attacked by phagocytic cells only when specific antibody is present. Granulocyte-mediated killing can be largely attributed to neutrophils. Eosinophils appear to play only a minor role and compete ineffectually when neutrophils are also present. The only group of protozoal species which may be significantly controlled by eosinophils are the stercorarian species of Trypanosoma. In vitro experiments show that antibody-coated trypomastigotes of T. cruzi can be killed by eosinophils, although there is little evidence that this occurs in vivo. Interestingly, this is the only species that has been reported to be susceptible to the major basic protein of eosinophils, a toxic component of the lysosomal granules which is very active against helminths. Neutrophils are not very active against endozoites of Toxoplasma gondii, Trypanosoma, trypomastigotes of salivarian Trypanosoma, free merozoites of Plasmodium, and promastigotes and amastigotes of Leishmania.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification and partial characterization of an extracellular acid phosphatase activity of Leishmania donovani promastigotes

An extracellular acid phosphatase was detected in the growth media of Leishmania donovani promastigotes. The enzyme was released at all stages of the growth cycle and in amounts which accounted for 90% of the total amount of this enzyme in the culture. The exoenzyme exhibited a pH optimum of 4.5 to 5.0 and was active with a variety of organic phosphates. The enzymatic activity was excluded from Sephacryl S-300 and was retained by ultrafilters with nominal molecular weight cutoffs of up to 300,000. The results of comparative studies indicated that the extracellular enzyme was distinct from a surface membrane-bound acid phosphatase of L. donovani promastigotes which has been previously described.

Cell surface origin of antigens shed by Leishmania donovani during growth in axenic culture

Antisera against isolated cell surface preparations (PCSP-As) of Leishmania donovani promastigotes were used to detect extracellular antigens produced during the growth of these organisms in four different growth media. The PCSP-As precipitated two major antigenically identical but electrophoretically distinct components, in addition to several minor antigens. Immunoelectrophoretic studies employing PCSP-As, PCSP-As absorbed with intact, live promastigotes, and PCSP-As absorbed with a major extracellular antigen demonstrated the antigenic identity between the major extracellular antigens and two major components externally disposed at the surface of promastigotes. Growth curve kinetic investigations suggested that the major extracellular antigens did not appear in the growth media primarily as a result of cell lysis or damage. The carbohydrate nature of the major extracellular antigens was indicated by physicochemical characterization.

Identification of galactose as the immunodominant sugar of leishmanial excreted factor and subsequent labeling with galactose oxidase and sodium boro[3H]hydride

Inhibition by low-molecular-weight sugars of precipitin line formation between a polysaccharide (EF) excreted by Leishmania tropica subsp. major, Leishmania enriettii, and rabbit antileishmanial antibodies on double gel diffusion plates revealed that galactose residues, possibly as components of lactosyl groups, were the critical immunodominant sugars mediating antibody recognition of EF. The galactose residues of the EF of L. tropica subsp. major were specifically labeled with tritium via galactose oxidase and sodium boro[3H]hydride. The radioactive EF had an apparent molecular weight of about 85,000 on sodium dodecyl sulfate-polyacrylamide gels and was precipitated by antileishmanial antibodies as well as Ricinus communis lectins I and II (galactose specific). Lectins specific for glucose-mannose residues, fucose, N-acetylglucosamine, and N-acetylgalactosamine did not precipitate the labeled EF. Treatment of [3H]EF with proteolytic (trypsin, papain, protease) or glycosidic (alpha-amylase, beta-galactosidase) enzymes had no effect on either the electrophoretic pattern of the material or on its recognition by antileishmanial antibodies or R. communis lectin. This resistance to enzyme activity suggests that EF may be a useful marker for the presence of the parasite in vivo if it can be detected in minute quantities.

Identification and partial characterization of an extracellular acid phosphatase activity of Leishmania donovani promastigotes

An extracellular acid phosphatase was detected in the growth media of Leishmania donovani promastigotes. The enzyme was released at all stages of the growth cycle and in amounts which accounted for 90% of the total amount of this enzyme in the culture. The exoenzyme exhibited a pH optimum of 4.5 to 5.0 and was active with a variety of organic phosphates. The enzymatic activity was excluded from Sephacryl S-300 and was retained by ultrafilters with nominal molecular weight cutoffs of up to 300,000. The results of comparative studies indicated that the extracellular enzyme was distinct from a surface membrane-bound acid phosphatase of L. donovani promastigotes which has been previously described.

Interactions between murine macrophages and obligate intracellular protozoa

The diversity of interactions between obligate intracellular protozoa and murine macrophages is just being elucidated. Protozoa of the genera Toxoplasma, Leishmania, and Trypanosoma all enter and replicate within macrophages. This review describes similarities and differences among these organisms with regard to entry mechanisms, sites of replication in the phagolysosomal system, metabolic requirements, effects on macrophage function, macrophage handling of protozoal antigens, the relationship to genetics of immune response, and the characteristics of lymphokine-induced microbicidal and microbistatic processes. These organisms each enter the macrophage by endocytosis, but they then reside at different sites in relation to the phagolysosomal system. The basis of obligate parasitism remains unknown; however, both the protozoa and the host cell have important effects on the function of the other during parasitism. The macrophage may play a pivotal role in the immunosuppression associated with the early stages of infection by each of these microbes. Genetic influences on the response to infection have been clearly identified in murine models. Lymphocyte products from immune cells have marked effects on the interactions of protozoa and macrophages, under some conditions stimulating protozoacidal mechanisms, and in some protozoastatic responses. The dynamic balance between protozoal parasitism and macrophage response must be further defined in order to determine the potential value of chemotherapeutic or immunologic intervention.

Production and secretion of Leishmania braziliensis proteins

The kinetics of secretion of proteins by Leishmania braziliensis was followed by incorporation of [3H]leucine into macromolecules produced by the cells which are released into the growth medium. About 10% of the total protein synthesized by actively growing cells is secreted. Cycloheximide (100 microgram/ml) and puromycin (0.5 mM) inhibited the incorporation of labelled leucine by 85 and 99%, respectively. The secreted proteins do not seem to result from cell lysis since, first, the kinetics of production are linear and, secondly, less than 1% of thymidine or uridine incorporated by the cells is found in the medium. Cells grown with [3H]leucine and then transferred to fresh medium show two phases of secretion. During the first six hours, it is slow and reaches a plateau. The release increases about ten-fold during the next six hours. An analysis of the secreted material showed that following precipitation with methanol and sodium acetate, three isotopically labelled peaks were eluted from Sephadex G-120-150. The first of these, containing 50% of the radioactivity, did not react with anti-leishmanial serum, while the last two did. Since the last two fractions could be labelled with [3H]glucosamine as well as [3H]leucine it is suggested that they are glycoprotein in nature and are similar to the products released by other species of Leishmania.