Key differences between olfactory ensheathing cells and Schwann cells regarding phagocytosis of necrotic cells: implications for transplantation therapies.

Transplantation of peripheral nervous system glia is being explored for treating neural injuries, in particular central nervous system injuries. These glia, olfactory ensheathing cells (OECs) and Schwann cells (SCs), are thought to aid regeneration by clearing necrotic cells, (necrotic bodies, NBs), as well as myelin debris. The mechanism by which the glia phagocytose and traffic NBs are not understood. Here, we show that OECs and SCs recognize phosphatidylserine on NBs, followed by engulfment and trafficking to endosomes and lysosomes. We also showed that both glia can phagocytose and process myelin debris. We compared the time-course of glial phagocytosis (of both NBs and myelin) to that of macrophages. Internalization and trafficking were considerably slower in glia than in macrophages, and OECs were more efficient phagocytes than SCs. The two glial types also differed regarding their cytokine responses after NB challenge. SCs produced low amounts of the pro-inflammatory cytokine TNF-α while OECs did not produce detectable TNF-α. Thus, OECs have a higher capacity than SCs for phagocytosis and trafficking, whilst producing lower amounts of pro-inflammatory cytokines. These findings suggest that OEC transplantation into the injured nervous system may lead to better outcomes than SC transplantation.

Stimulating the proliferation, migration and lamellipodia of Schwann cells using low-dose curcumin.

Transplantation of peripheral glia is being trialled for neural repair therapies, and identification of compounds that enhance the activity of glia is therefore of therapeutic interest. We have previously shown that curcumin potently stimulates the activity of olfactory glia. We have now examined the effect of curcumin on Schwann cell (SC) activities including proliferation, migration and the expression of protein markers. SCs were treated with control media and with different concentrations of curcumin (0.02-20 µM). Cell proliferation was determined by MTS assay and migration changes were determined by single live cell migration tracking. We found that small doses of curcumin (40 nM) dramatically increased the proliferation and migration in SCs within just one day. When compared with olfactory glia, curcumin stimulated SC proliferation more rapidly and at lower concentrations. Curcumin significantly increased the migration of SCs, and also increased the dynamic activity of lamellipodial waves which are essential for SC migration. Expression of the activated form of the MAP kinase p38 (p-p38) was significantly decreased in curcumin-treated SCs. These results show that curcumin's effects on SCs differ remarkably to its effects on olfactory glia, suggesting that subtypes of closely related glia can be differentially stimulated by curcumin. Overall these results demonstrate that the therapeutically beneficial activities of glia can be differentially enhanced by curcumin which could be used to improve outcomes of neural repair therapies.

Amiodarone inhibits Trypanosoma cruzi infection and promotes cardiac cell recovery with gap junction and cytoskeleton reassembly in vitro.

We present the results of the first detailed study of the antiproliferative and ultrastructural effects of amiodarone on Trypanosoma cruzi, the causative agent of Chagas' disease. Moreover, we report the effects of this compound on the recovery of F-actin fibrils, connexin43, and contractility in T. cruzi-infected cardiac myocytes. Amiodarone is the most prescribed class III antiarrhythmic agent and is frequently used for the symptomatic treatment of Chagas' disease patients with cardiac compromise. In addition, recent studies identified its antifungal and antiprotozoal activities, which take place through Ca(2+) homeostasis disruption and ergosterol biosynthesis blockade. We tested different concentrations of amiodarone (2.5 to 10 µM) on infected primary cultures of heart muscle cells and observed a dose- and time-dependent effect on growth of the clinically relevant intracellular amastigote form of T. cruzi. Ultrastructural analyses revealed that amiodarone had a profound effect on intracellular amastigotes, including mitochondrial swelling and disorganization of reservosomes and the kinetoplast and a blockade of amastigote-trypomastigote differentiation. Amiodarone showed no toxic effects on host cells, which recovered their F-actin fibrillar organization, connexin43 distribution, and spontaneous contractility concomitant with the drug-induced eradication of the intracellular parasites. Amiodarone is, therefore, a promising compound for the development of new drugs against T. cruzi.

Small molecule inhibitors of lysozyme amyloid aggregation.

Protein amyloid aggregation is associated with a number of important human pathologies, but the precise mechanisms underlying the toxicity of amyloid aggregates are still incompletely understood. In this context, drugs capable of blocking or interfering with the aggregation of amyloidogenic proteins should be considered in strategies aimed at the development of novel therapeutic agents. Human lysozyme variants have been shown to form massive amyloid deposits in the livers and kidneys of individuals affected by hereditary systemic amyloidosis. Currently, there are no clinical treatments available to prevent or reverse formation of such amyloid deposits. We have recently described a number of di- and trisubstituted aromatic compounds that block the formation of soluble oligomers and amyloid fibrils of the beta-amyloid peptide (Abeta) and protect hippocampal neurons in culture from Abeta-induced toxicity. Here, we show that some of those compounds inhibit the formation and disrupt preformed amyloid fibrils from both human and hen egg white lysozyme. These results suggest that these small molecule compounds may serve as prototypes for the development of drugs for the prevention or treatment of different types of amyloidoses.

Uptake of host cell transforming growth factor-beta by Trypanosoma cruzi amastigotes in cardiomyocytes: potential role in parasite cycle completion.

The cytokine transforming growth factor-beta (TGF-beta) plays various functions in the control of Trypanosoma cruzi infectivity and in the progression of Chagas' disease. When we immunostained T. cruzi-infected cardiomyocytes (after either in vivo or in vitro infections) for TGF-beta, we observed stronger immunoreactivity in parasites than in host cells. TGF-beta immunoreactivity evolved during parasite cycle progression, with intense staining in amastigotes versus very faint staining in trypomastigotes. TGF-beta was present on the surface of amastigotes, in the flagellar pocket, and in intraparasitic vesicles as revealed by electron microscopy. However, no ortholog TGF-beta gene could be identified in the genome of T. cruzi by in silico analysis or by extensive polymerase chain reaction and reverse transcriptase-polymerase chain reaction studies. Immunoreactive TGF-beta was most probably taken up by the parasite from the host cell cytoplasm because such an internalization process of biotinylated TGF-beta could be observed in axenic amastigotes in vitro. These observations represent the first example of a novel mechanism by which a primitive unicellular protozoan can use host cell TGF-beta to control its own intracellular life cycle.

Microscopy images as interactive tools in cell modeling and cell biology education.

The advent of genomics, proteomics, and microarray technology has brought much excitement to science, both in teaching and in learning. The public is eager to know about the processes of life. In the present context of the explosive growth of scientific information, a major challenge of modern cell biology is to popularize basic concepts of structures and functions of living cells, to introduce people to the scientific method, to stimulate inquiry, and to analyze and synthesize concepts and paradigms. In this essay we present our experience in mixing science and education in Brazil. For two decades we have developed activities for the science education of teachers and undergraduate students, using microscopy images generated by our work as cell biologists. We describe open-air outreach education activities, games, cell modeling, and other practical and innovative activities presented in public squares and favelas. Especially in developing countries, science education is important, since it may lead to an improvement in quality of life while advancing understanding of traditional scientific ideas. We show that teaching and research can be mutually beneficial rather than competing pursuits in advancing these goals.

Formation of amyloid aggregates from human lysozyme and its disease-associated variants using hydrostatic pressure.

Formation of amyloid deposits from the Ile56Thr or Asp67His variants of human lysozyme is a hallmark of autosomal hereditary systemic amyloidosis. It has recently been shown that amyloid fibrils can be formed in vitro from wild-type (WT), I56T, or D67H lysozyme variants upon prolonged incubation at acidic pH and elevated temperatures (1). Here, we have used hydrostatic pressure as a tool to generate amyloidogenic states of WT and variant lysozymes at physiological pH. WT or variant lysozyme samples were initially compressed to 3.5 kbar (at 57 degrees C, pH 7.4). Decompression led to the formation of amyloid fibrils, protofibrils, or globular aggregates, as indicated by light scattering, thioflavin T fluorescence, and transmission electron microscopy analysis. Increased 1-anilinonaphthalene-8-sulfonate binding to the proteins was also observed, indicating exposure of hydrophobic surface area. Thus, pressure appears to induce a conformational state of lysozyme that aggregates readily upon decompression. These results support the notion that amyloid aggregation results from the formation of partially unfolded protein conformations and suggest that pressure may be a useful tool for the generation of the amyloidogenic conformations of lysozyme and other proteins.

Selective in vitro effects of the farnesyl pyrophosphate synthase inhibitor risedronate on Trypanosoma cruzi.

We present the results of the first detailed study of the molecular and cellular basis of the antiproliferative effects of the bisphosphonate risedronate (Ris) on Trypanosoma cruzi, the causative agent of Chagas' disease. Ris and related compounds, which block poly-isoprenoid biosynthesis at the level of farnesyl pyrophosphate synthase, are currently used for the treatment of bone resorption disorders, but also display selective activity against trypanosomatid and apicomplexan parasites. Ris induced a dose-dependent effect on growth of the extracellular epimastigote form of T. cruzi; complete growth arrest and cell lysis ensued at 150 microM. Growth inhibition was associated with depletion of the parasite's endogenous sterols, but complete growth arrest and loss of cell viability took place before full depletion of these compounds, suggesting that disappearance of other essential poly-isoprenoids is involved in its anti-parasitic action. Ris had a variety of effects on cellular ultrastructure, including mitochondrial swelling, disorganisation of other organelles, such as reservosomes and the kinetoplast, together with the appearance of autophagic vesicles and progressive vacuolization of the cytoplasm. Ris had selective antiproliferative effects against the clinically relevant amastigote form of T. cruzi, and at 100 microM, was able to prevent completely the development of T. cruzi infection of murine muscle heart or Vero cells, and to cure cultures which were already infected. Ris induced drastic ultrastructural alterations in the intracellular parasites and blocked amastigote to trypomastigote differentiation, with no biochemical or ultrastructural effects on the host cells, which fully recovered their normal structure and activity after treatment. Ris is, therefore, a promising lead compound for the development of new drugs against T. cruzi.

Antiparasitic activity of risedronate in a murine model of acute Chagas' disease.

We report the results of a study on the activity of the farnesyl-pyrophosphate synthase inhibitor risedronate (Ris) in a murine model of acute Chagas' disease. This compound displays rapid, cytocidal activity in vitro against Trypanosoma cruzi, but its in vivo activity had not been investigated previously. A murine model of acute Chagas' disease was used, in which experimental animals were infected with 10(3) trypomastigotes and intravenous treatment was started 24 h post-infection. In this model, Ris, at doses as low as 1 mg/kg per day given for 7 days, induced > 90% reductions in parasitaemia and increased very significantly (P = 0.001) the survival of treated animals. Higher doses (up to 10 mg/kg per day) led to further reductions in parasitaemia and mortality, with no deleterious effects on weight gain and general physical condition of the treated animals. There was no relapse of parasitaemia after discontinuation of treatment, suggesting trypanocidal, rather than trypanostatic, activity. This interpretation was confirmed by the almost complete disappearance of amastigote nests in the hearts of treated animals. However, no parasitological cures were observed in infected animals that received the bisphosphonate, probably due to the short treatment period. Taken together, these results indicate that Ris could be a useful lead compound for the development of new drugs effective against Chagas' disease.

Reduced activity of matrix metalloproteinase-9 in trypanosoma cruzi-infected mouse embryo hepatocyte cell.

In this work, we are reporting differences in the proteolytic profile of Trypanosoma cruzi-infected and non-infected primary cultures of mouse embryo hepatocyte cells. In gelatin-SDS-PAGE, ours results showed the presence of a 100kDa metalloproteinase in the supernatant and in the cells of both systems and an 85kDa extracellular metalloproteinase found only in the non-infected hepatocyte cultures. An enzymatic assay using gelatin as substrate showed a decrease of 74 and 70% in metalloproteinase activity in the culture supernatant and in the cell hepatocyte system infected with T. cruzi, respectively. Western blotting analysis using anti-matrix metalloproteinase-9 (MMP-9) antibody recognized the 100 and 85kDa protein bands, indicating that hepatocyte metalloproteinases correspond to the latent and active forms of the gelatinase MMP-9, respectively. The localization of MMP-9 was established by immunocytochemistry analysis in the cytoplasm of the non-infected and infected hepatocyte cells. In normal and infected hepatocyte cells, cysteine-proteinases migrating in gelatin-SDS-PAGE at 60kDa were detected and should correspond to lysosomal cysteine-proteinases of T. cruzi (cruzipain) and hepatocytes. In T. cruzi-infected hepatocytes an increase of approximately 50% in this enzymatic activity was observed, possibly due to parasite's cruzipain.

Ultrastructural features of the midgut epithelium of females Lutzomyia intermedia (Lutz & Neiva, 1912) (Diptera: Psychodidae: Phlebotominae)

A morphological study of the midgut of Lutzomyia intermedia, the primary vector of cutaneous leishmaniasis, in southeast Brazil, was conducted by light, scanning and transmission electron microscopy. The midgut is formed by a layer of epithelium of columnar cells on a non-cellular basal lamina, under which there is a musculature, which consists of circular and longitudinal muscular fibers. A tracheolar network is observed surrounding and penetrating in the musculature. Females were examined 12, 24, 48, 72 h and 5 days following a blood meal and were analyzed comparatively by transmission electron microscopy with starved females. In starved females, the epithelium of both the anterior and posterior sections of the midgut present whorl shaped rough endoplasmic reticulum. The posterior section does not present well-developed cellular structures such as mitochondria. Observations performed at 12, 24, 48 and 72 h after the blood meal showed morphological changes in the cellular structures in this section, and the presence of the peritrophic matrix up to 48 h after the blood meal. Digestion is almost complete and a few residues are detected in the lumen 72 h after blood feeding. Finally, on the 5th day after the blood meal all cellular structures present the original feature resembling that seen in starved sand flies. Morphometric data confirmed the morphological observations. Mitochondria, nuclei and microvilli of midgut epithelial cells are different in starved and blood fed females. The mitochondria present a similar profile in the epithelium of both the anterior and posterior section of the midgut, with higher dimension in starved females. The cell microvilli in the posterior section of the midgut of starved females are twice the size of those that had taken a blood meal. We concluded that there are changes in the midgut cellular structures of L. intermedia during the digestion of blood, which are in agreement with those described for other hematophagous diptera

A C619Y mutation in the human androgen receptor causes inactivation and mislocalization of the receptor with concomitant sequestration of SRC-1 (steroid receptor coactivator 1)

Androgen ablation therapy is a primary treatment for advanced prostate cancer, but tumors become refractive to therapy. Consequently, the role of the androgen receptors (ARs) and of mutations in the AR in prostate cancer has been a subject of much concern. In the course of analyzing tumors for mutations, we identified a somatic mutation that substitutes tyrosine for a cysteine at amino acid 619 (C619Y), which is near the cysteines that coordinate zinc in the DNA binding domain in the AR. The mutation was re-created in a wild-type expression vector and functional analyses carried out using transfection assays with androgen-responsive reporters. The mutant is transcriptionally inactive and unable to bind DNA. In response to ligand treatment, AR619Y localizes abnormally in numerous, well circumscribed predominantly nuclear aggregates in the nucleus and cytoplasm. Interestingly, these aggregates also contain the bulk of the coexpressed steroid receptor coactivator SRC-1, suggesting, in analogy to AR in spinal bulbar muscular atrophy, that this mutant may alter cellular physiology through sequestration of critical proteins. Although many inactivating mutations have been identified in androgen insensitivity syndrome patients, to our knowledge, this is the first characterization of an inactivating mutation identified in human prostate cancer.

Extracellular serine-proteinases isolated from Streptomyces alboniger: Partial characterization and effect of aprotinin on cellular structure

Streptomyces alboniger ATCC 12461 grown in brain heart infusion (BHI) medium produced two extracellular serine-proteinases, denoted SP I and SP II, which were purified by ammonium sulfate precipitation and aprotinin-agarose affinity chromatography. SP I was purified 88,9-fold and SP II 66,7- fold, with 33.4 percent and 10.4 percent yield, respectively. The optimum pH for the proteinases activity, using a-N-p-tosyl-L-arginine-methyl ester (TAME) as substrate, was 9-10 and the optimum temperature was 37ºC. The proteolytic activity of SP I and SP II was inhibited by aprotinin and SP I was partially inhibited by leupeptin, both serine-proteinase inhibitors. S. alboniger growth in BHI-liquid medium decreased when 5 mg/ml, 10 mg/ml of aprotinin was used, being completely inhibited with 20 mg/ml and 40 mg/ml. At the ultrastructural level, aprotinin-treated S. alboniger cells showed swelling of the bacterial body and condensation of the genetic material, probably related to the inhibition of its growth

7alpha-Iodo and 7alpha-fluoro steroids as androgen receptor-mediated imaging agents.

We have synthesized several 7alpha-fluoro (F) and 7alpha-iodo (I) analogues of 5alpha-dihydrotestosterone (5alpha-DHT) and 19-nor-5alpha-dihydrotestosterone (5alpha-NDHT) and tested them for binding to the androgen receptor and for their biological activity in an in vitro assay with cells that have been engineered to respond to androgens. The relative binding affinity to the androgen receptor determined in competition assays showed that in the androstane series the fluoro steroids have the highest affinity and that F-17alpha-CH3-DHT (4) has a higher affinity than 5alpha-DHT. All other steroids were somewhat less potent than 5alpha-DHT with F-DHT (2) = I-17alpha-CH3-DHT (3) >/= F-NDHT (6) > F-17alpha-CH3-NDHT (8) = I-DHT (1) >/= I-NDHT (5) > I-17alpha-CH3-NDHT (7). The relative biological activity in cells transfected with the androgen receptor and an androgen responsive reporter gene is 4 >> 5alpha-DHT > 2 > 6 > 3 >/= 1 >/= 8 >/= 5 > 7. The iodinated compound, I-17alpha-CH3-DHT (3), with the highest binding activity was synthesized labeled with 125I and was shown to bind with high affinity, Ka = 1.9 x 10(10) L/mol, and low nonspecific binding to the androgen receptor in rat prostatic cytosol. However, when radiolabeled [125I]-17alpha-CH3-DHT ([125I]3) was injected into castrated male rats, it showed very poor androgen receptor-mediated uptake into the rat prostate. This was unexpected in light of its superior receptor binding properties and its protection by the 17alpha-methyl group from metabolic oxidation at C-17. However, the biological potency of I-17alpha-CH3-DHT (3) was not as high as would have been expected. When I-DHT (1) and I-17alpha-CH3-DHT (3) were incubated in aqueous media at 37 degrees C they rapidly decomposed, but they were stable at 0 degrees C. The fluorinated analogue 4 treated similarly at 37 degrees C was completely stable. The products of the decomposition reaction of I-DHT (1) at 37 degrees C were identified as iodide and principally 17beta-hydroxy-5alpha-androst-7-en-3-one. The temperature dependence of this elimination reaction explains the inconsistency between the high binding to the androgen receptor (measured at 0 degrees C) and the low biological activity, as well as the poor androgen receptor mediated concentration in vivo. The fluorinated analogue F-17alpha-CH3-DHT (4) has both high affinity for the androgen receptor and high stability in aqueous media. Of the compounds tested, 4 has the highest affinity for the androgen receptor as well as the highest androgenic activity. Thus it is likely that F-17alpha-CH3-DHT 4 labeled with 18F will be an excellent receptor-mediated diagnostic imaging agent.

Use of the detergent Triton in biochemical and biological research: a minireview

The use of nonionic detergents such as Triton X-100 and X-114, is of immense value in biological and biochemical research. These detergents have found numerous applications in the analysis of membrane proteins, enzymes, glycoconjugates and in the study of cytoskeleton structure. The method offers an excellent resolution when used in coordination with immunological methods such as, immunoelectrophoresis, immunoprecipitation and western blot analysis.

Transfected glucocorticoid receptor and certain GR fragments evoke cell death in malignant lymphoid, not myeloid cell lines.

Previously we have shown that glucocorticoid sensitivity could be restored to a clone of glucocorticoid-resistant leukemic T cells by transfecting them with an expression vector for the glucocorticoid receptor. Furthermore, transfection with plasmids expressing fragments of the receptor containing the DNA-binding domain resulted in constitutive loss of cells. In this paper, we report the results of transfecting both types of constructs into lines of glucocorticoid-resistant human leukemic cells of T cell, B cell, and myeloid origin. In all the lymphoid lines tested, transfection of the holoreceptor gene resulted in appearance of steroid-dependent cell death. In the same lines, transfection of glucocorticoid receptor fragments expressing amino acids 1-465* (465 residues of the normal sequence plus a novel 21 amino acid C-terminus) or expressing only 398-465* caused cell death without the addition of steroids. The amount of cell loss following transfection of these constitutively lethal fragments was in the same range as that following transfection of the holo glucocorticoid receptor plus administration of glucocorticoid. However, the cell loss due to the constitutively active fragments occurred more rapidly. Neither of the myeloid lines tested were sensitive to any of the transfected constructs, with or without added steroid.

Activation of the human androgen receptor through a protein kinase A signaling pathway.

Aberrant activation of the androgen receptor through signaling pathways independent of androgen may be responsible for the progression of prostate tumors to the rapidly proliferating androgen-independent state. In this study, the effects of protein kinase A modulators on human androgen receptor activity were tested. Using an adenoviral DNA delivery system, we demonstrate that the androgen receptor can be activated by a protein kinase A activator, forskolin, in the absence of androgen when androgen receptor is co-transfected into monkey kidney CV1 cells or human prostate PC-3 cells with androgen-responsive reporters. Immunoblotting reveals that there is no significant change in androgen receptor protein level following forskolin treatment, suggesting that the enhanced activity is due to activation of the receptor. This activation can be blocked by a protein kinase A inhibitor peptide. Two potent anti-androgens, casodex and flutamide, can significantly reduce this activation, confirming that the ligand-independent pathway is an androgen receptor-mediated phenomenon. An intact DNA binding domain of the receptor is critical for this alternate signaling pathway since mutants with reduced DNA binding ability are inactive. The phosphorylation status of the androgen receptor or associated proteins may critically modulate receptor activity and should be considered when designing improved approaches to prostate cancer therapy.

Glucocorticoids in malignant lymphoid cells: gene regulation and the minimum receptor fragment for lysis.

We have examined clones of human malignant lymphoid cells for markers that correlate with glucocorticoid-mediated cell lysis. In glucocorticoid-sensitive clones of CEM, a human T-cell lymphoblastic leukemia line, two genes correlate with glucocorticoid-induced cell lysis. The glucocorticoid receptor (GR) itself is induced by standard glucocorticoids in sensitive clones and not in insensitive clones. The phenylpyrazolo-glucocorticoid cortivazol (CVZ) is capable of lysing several clones resistant to high concentrations of standard potent glucocorticoids. When these clones were tested for cortivazol responses, they were not only lysed by cortivazol but also showed induction of GR mRNA. Thus receptor induction appears to correlate with the lysis function of receptor in these cells. To determine what parts of the GR are required for lysis, we have mapped this function by transfecting and expressing GR and GR fragment genes in a GR-deficient CEM clone. Our results indicate that none of the known trans-activation regions of the GR are required. Removal of the steroid binding domain gives a fragment that is fully constitutive. Only one and one-half "Zn fingers" of the DNA binding region are required. We also find in CEM cells rapid suppression of the c-myc protooncogene, preceding growth arrest and cell lysis by glucocorticoids. This occurs only in clones possessing both intact receptors and lysis function. Thus the simple presence of GR alone is not sufficient to guarantee c-myc down-regulation. Introduction into the cells of c-myc driven by a promoter that does not permit suppression by glucocorticoids confers resistance to steroids. Furthermore, suppression of c-myc by antisense oligonucleotides also kills the cells. Therefore, c-myc appears to be a pivotal gene related both to ability of steroid to kill and to cell viability.

Trypanosoma cruzi recognition by macrophages and muscle cells: perspectives after a 15-year study

Macrophages and muscle cells are the main targets for invasion of Trypanosoma cruzi. Ultrastructural studies of this phenomenon in vitro showed that invasion occurs by endocytosis, with attachment and internalization being mediated by different components capable of recognizing epi-or trypomastigotes (TRY). A parasitophorus vacuole was formed in both cell types, thereafter fusing with lysosomes. Then, the mechanism of T. cruzi invasion of host cells (HC) is essentially similar (during a primary infection in the abscence of a specific immune response), regardless of wether the target cell is a professional or a non-professional phagocytic cell. Using sugars, lectins, glycosidases, proteinases and proteinase inhibitors, we observed that the relative balance between exposed sialic acid and galactose/N-acetyl galactosamine (GAL) residues on the TRY surface, determines the parasite's capacity to invade HC, and that lectin-mediated phagocytosis with GAL specificity is important for internalization of T. cruzi into macrophages. On the other hand, GAL on the surface to heart muscle cells participate on TRY adhesion. TRY need to process proteolytically both the HC and their own surface, to expose the necessary ligands and receptors that allow binding to, and internalization in the host cell. The diverse range of molecular mechanisms which the parasite could use to invade the host cell may correspond to differences in the available "receptors"on the surface of each specific cell type. Acute phase components, with lectin or proteinase inhibitory activities (a-macroglobulins), may also be involved in T. cruzi-host cell interaction