Identification of immunodominant epitopes in Trypanosoma cruzi trypomastigote surface antigen-1 protein that mask protective epitopes

The gene that encodes trypomastigote surface Ag-1 (TSA-1), a major surface Ag of the bloodstream trypomastigote stage of Trypanosoma cruzi, was expressed in a baculovirus expression system. To determine the epitope(s) in TSA-1 that was recognized during T. cruzi infection and after immunization with TSA-1, subregions of the TSA-1 gene were expressed in a bacterial expression system. As seen by Western blotting, both mice and rabbits immunized with recombinant TSA-1 protein, as well as T. cruzi-infected mice, developed strong immune responses to the carboxyl-proximal region of TSA-1, but show no reaction to the amino-proximal portion of TSA-1. When mice were immunized with either recombinant TSA-1 protein or the carboxyl-proximal region of TSA-1, they did not survive challenge with 10(3) bloodstream trypomastigotes. However, 70% of the mice immunized with the amino-proximal portion of TSA-1 survived challenge with 10(3) bloodstream trypomastigotes. Thus, the immune responses elicited by recombinant TSA-1 or the carboxyl-proximal portion of TSA-1 are nonprotective during T. cruzi infection. In contrast, vaccination with the amino proximal region of TSA-1 elicits a protective immune response. These results suggest that responses to immunodominant epitope(s) within the carboxyl-proximal portion of TSA-1 mask epitopes within the amino-proximal portion that are capable of stimulating host-protective immune responses. It is suggested that immunodominant regions in surface molecules such as TSA-1 may provide a mechanism for the parasite to evade the host immune response by directing the response away from epitopes that have the potential to elicit a reaction that is damaging to the parasite.

Identification of immunodominant epitopes in Trypanosoma cruzi trypomastigote surface antigen-1 protein that mask protective epitopes

The gene that encodes trypomastigote surface Ag-1 (TSA-1), a major surface Ag of the bloodstream trypomastigote stage of Trypanosoma cruzi, was expressed in a baculovirus expression system. To determine the epitope(s) in TSA-1 that was recognized during T. cruzi infection and after immunization with TSA-1, subregions of the TSA-1 gene were expressed in a bacterial expression system. As seen by Western blotting, both mice and rabbits immunized with recombinant TSA-1 protein, as well as T. cruzi-infected mice, developed strong immune responses to the carboxyl-proximal region of TSA-1, but show no reaction to the amino-proximal portion of TSA-1. When mice were immunized with either recombinant TSA-1 protein or the carboxyl-proximal region of TSA-1, they did not survive challenge with 10(3) bloodstream trypomastigotes. However, 70% of the mice immunized with the amino-proximal portion of TSA-1 survived challenge with 10(3) bloodstream trypomastigotes. Thus, the immune responses elicited by recombinant TSA-1 or the carboxyl-proximal portion of TSA-1 are nonprotective during T. cruzi infection. In contrast, vaccination with the amino proximal region of TSA-1 elicits a protective immune response. These results suggest that responses to immunodominant epitope(s) within the carboxyl-proximal portion of TSA-1 mask epitopes within the amino-proximal portion that are capable of stimulating host-protective immune responses. It is suggested that immunodominant regions in surface molecules such as TSA-1 may provide a mechanism for the parasite to evade the host immune response by directing the response away from epitopes that have the potential to elicit a reaction that is damaging to the parasite.

Dosage compensation in Drosophila: the X-chromosomal binding of MSL-1 and MLE is dependent on Sxl activity

In Drosophila, dosage compensation, i.e. the equalization of levels of X-linked gene products in the two sexes, is achieved by the hypertranscription of most X-linked genes in males relative to females. The products of at least four genes, collectively termed male-specific lethal (msl) genes, are required for this process and, at least in the case of three of them, mediate this function through an association with the X chromosome in males. We have studied some of the parameters that affect the association of the msl-1 gene product and found that its presence is dependent on the wild-type function of the other three genes, leading to the conclusion that these gene products contribute to the formation of a multi-subunit complex. Furthermore, the X-chromosomal association of the msl-1 and mle gene products is negatively correlated with the level of function of the master regulatory gene Sxl and can assume either a mosaic or a uniform distribution in the tissues of mutant XX individuals. Surprisingly, we also found that the association of these two msl gene products with the two X chromosomes in females of certain mutant genotypes does not result in the hypertranscription of X-linked genes or in any apparent reduction in viability.

A comparative study of the aggregation of human, rat and rabbit platelets by members of the Streptococcus sanguis group

Aggregation of platelets by bacteria is a potential factor in the pathogenesis of infective endocarditis. Twenty-five strains from the Streptococcus sanguis group, including 15 recent isolates from cases of endocarditis, were compared for their ability to aggregate human and rat platelets over periods of 15 and 25 min, respectively. In each case, 76% of strains caused aggregation; the median time to onset of aggregation was longer for human platelets (12 min) than for rat platelets (1 min). Strains unable to aggregate human platelets included three from cases of endocarditis. There was no correlation between the ability to aggregate human and rat platelets, although the majority of strains (60%) aggregated both. Tests on representative strains for their ability to aggregate rabbit platelets gave results similar to those for rat platelets, including a median time of 1 min to onset of aggregation. The differences in the ability of individual bacterial strains to aggregate human and animal platelets indicate that caution is needed in extrapolating in-vitro observations to the in-vivo situation.

Autocrine growth stimulation of human renal Wilms' tumour G401 cells by a gastrin-like peptide

The role of gastrin in the control of growth of renal G401 cells isolated from a human nephroblastoma (Wilms' tumour) was investigated. G401 cell growth was enhanced in the presence of exogenous gastrin. Addition of anti-gastrin antibodies to serum-free medium significantly inhibited the growth of G401 cells. G401 cells contained the equivalent of 4.3 pg/10(6) cells of gastrin, and serum-free medium collected over 48 hr from G401 cells contained the equivalent of 38 ng/10(6) cells of gastrin, as determined by radioimmunoassay. Growth of G401 cells was inhibited in a concentration-related way by a variety of gastrin/CCK receptor antagonists. Devazepide and proglumide were, respectively, the most and the least potent inhibitors of G401 cell growth (potency order devazepide > L-365,260 = lorglumide > loxiglumide > benzotript > proglumide). These gastrin/CCK receptor antagonists had similar growth-inhibitory activities in human colonic adenocarcinoma HCT-116 cells. Growth of HCT-116 cells was stimulated to a lesser extent, as compared with G401 cells, by exogenous gastrin, and endogenous gastrin was not detectable in HCT-116 cells. The results are consistent with a role for a gastrin-like peptide in the control of growth of a renal cell line. The data suggest that gastrin/CCK receptor antagonists warrant further investigation as therapeutic agents for the control of gastrin-responsive tumours derived from outside, as well as inside, the gastrointestinal tract, including tumours derived from the kidney.

An appraisal of the virulence factors associated with streptococcal endocarditis

Platelet aggregation is believed to be a virulence factor in infective endocarditis. Other factors may be adhesion to components of thrombotic vegetations, particularly platelets, fibronectin and fibrinogen. Two strains from the Streptococcus sanguis group (SSG) were chosen for comparative study on the basis that one aggregated both human and rat platelets and the other lacked this capacity. Both strains caused endocarditis in the rat model but the aggregating strain was found in higher numbers in the excised vegetations. The nonaggregating strain was unable to bind to human or rat platelets but could bind insoluble fibronectin, insoluble fibrinogen and platelet-fibrin clots from both sources, albeit to a lesser extent than the aggregating strain. These results suggest that whereas adhesion to, and aggregation of, platelets are not essential events in the initiation of the pathogenesis of experimental endocarditis, they may be factors contributing to virulence.

Expression and evolution of members of the Trypanosoma cruzi trypomastigote surface antigen multigene family

The trypomastigote specific surface antigens of Trypanosoma cruzi are encoded by a supergene family which includes the TSA family. The TSA family is characterized by the presence of a 27-bp tandem repeat array in the coding region. Here, we report the characterization and analysis of the three TSA family members in the Esmeraldo strain of the parasite. In this strain 2 distinct telomeric members are expressed abundantly as 3.7-kb mRNAs, while the remaining member is located at an internal chromosomal site and is expressed at less than 2% of the level seen for the telomeric members. Based on hybridization to DNA separated by PFGE, 3 chromosomes of sizes 1.8 Mb, 0.98 Mb, and 0.90 Mb each contain one of the telomeric members. In addition, the two smaller chromosomes also contain the single internal member. Since both chromosomes contain similar TSA family members, and vary only slightly in size, we suggest that they are homologues. Comparisons of the nucleotide sequences of the different members of the family show that the internal gene differs from the telomeric genes primarily in sequences found 3' of the repeat array. These comparisons also reveal that the three genes are analogous, supporting the hypothesis that short segments between the family members are exchanged by gene conversion events. We propose that similar conversion events between members of different gene families may generate some of the diversity found within the supergene family.

The male-specific lethal-one (msl-1) gene of Drosophila melanogaster encodes a novel protein that associates with the X chromosome in males

Male-specific lethal-one (msl-1) is one of four genes that are required for dosage compensation in Drosophila males. To determine the molecular basis of msl-1 regulation of dosage compensation, we have cloned the gene and characterized its products. The predicted msl-1 protein (MSL-1) has no significant similarity to proteins in the current data bases but contains an acidic N terminus characteristic of proteins involved in transcription and chromatin modeling. We present evidence that the msl-1 protein is associated with hundreds of sites along the length of the X chromosome in male, but not in female, nuclei. Our findings support the hypothesis that msl-1 plays a direct role in increasing the level of X-linked gene transcription in male nuclei.

Aortic arch versus central venous epinephrine during CPR

STUDY OBJECTIVE

To determine if delivery of epinephrine to the peripheral arterial system by an aortic arch catheter is more effective than central venous epinephrine administration during cardiac resuscitation.

DESIGN

Randomized, nonblinded, controlled trial.

TYPE OF PARTICIPANTS

Sixteen mongrel canines (25 to 31 kg).

INTERVENTIONS

Animals had aortic arch pressure, and right atrial pressure, superior vena cava infusion, and descending aortic arch infusion catheters placed using fluoroscopy. After ten minutes of ventricular fibrillation, three DC countershocks were delivered over one minute. If unsuccessful, CPR at 120 compressions per minute was begun, and at 60 seconds of CPR, epinephrine (1 mg/50 mL normal saline) was administered either through the superior vena cava or the aortic arch catheter followed by one more minute of CPR. Defibrillation then was attempted and, if unsuccessful, further resuscitative efforts followed advanced cardiac life support guidelines, except route and dose of epinephrine remained the same.

MEASUREMENTS AND MAIN RESULTS

Aortic arch pressure, right atrial pressure, and coronary perfusion pressure (diastolic aortic arch pressure minus diastolic right atrial pressure) were recorded continuously. Aortic arch pressure and coronary perfusion pressure increased more rapidly and to a greater magnitude with aortic arch-epinephrine than superior vena cava-epinephrine. Coronary perfusion pressure doubled by ten seconds in seven of eight in the aortic arch-epinephrine group versus none in the superior vena cava-epinephrine group. Aortic arch pressure and coronary perfusion pressure increases consistently plateaued within 60 seconds after aortic arch-epinephrine but not after superior vena cava-epinephrine. Return of spontaneous circulation was faster (P < .05) in the aortic arch-epinephrine group. Maximal coronary perfusion pressure after epinephrine correlated with the coronary perfusion pressure immediately before epinephrine administration in both groups, but more strongly in the aortic arch-epinephrine group (P = .0001).

CONCLUSION

For an equivalent dose of epinephrine, aortic arch administration produces a more rapid response and more rapid peak effect than central venous administration. The combination of aortic arch-epinephrine administration and aortic pressure monitoring may be useful when initial standard resuscitative measures have not been successful.

Endothelial cell cytosolic free calcium regulates neutrophil migration across monolayers of endothelial cells

Polymorphonuclear leukocytes (PMN) traverse an endothelial cell (EC) barrier by crawling between neighboring EC. Whether EC regulate the integrity of their intercellular adhesive and junctional contacts in response to chemotaxing PMN is unresolved. EC respond to the binding of soluble mediators such as histamine by increasing their cytosolic free calcium concentration ([Ca++]i) (Rotrosen, D., and J.I. Gallin. 1986. J. Cell Biol. 103:2379-2387) and undergoing shape changes (Majno, G., S. M. Shea, and M. Leventhal. 1969. J. Cell Biol. 42:617-672). Substances such as leukotriene C4 (LTC4) and thrombin, which increased the permeability of EC monolayers to ions, as measured by the electrical resistance of the monolayers, transiently increased EC [Ca++]i. To determine whether chemotaxing PMN cause similar changes in EC [Ca++]i, human umbilical vein endothelial cells (HUVEC) maintained as monolayers were loaded with fura-2. [Ca++]i was measured in single EC during PMN adhesion to and migration across these monolayers. PMN-EC adhesion and transendothelial PMN migration in response to formyl-methionyl-leucyl-phenylalanine (fMLP) as well as to interleukin 1 (IL-1) treated EC induced a transient increase in EC [Ca++]i which temporally corresponded with the time course of PMN-EC interactions. When EC [Ca++]i was clamped at resting levels with a cell permeant calcium buffer, PMN migration across EC monolayers and PMN induced changes in EC monolayer permeability were inhibited. However, clamping of EC [Ca++]i did not inhibit PMN-EC adhesion. These studies provide evidence that EC respond to stimulated PMN by increasing their [Ca++]i and that this increase in [Ca++]i causes an increase in EC monolayer permeability. Such [Ca++]i increases are required for PMN transit across an EC barrier. We suggest EC [Ca++]i regulates transendothelial migration of PMN by participating in a signal cascade which stimulates EC to open their intercellular junctions to allow transendothelial passage of leukocytes.

Evidence for two distinct major protein components, PAR 1 and PAR 2, in the paraflagellar rod of Trypanosoma cruzi. Complete nucleotide sequence of PAR

The previously identified major protein components of the paraflagellar rod in Trypanosoma cruzi, PAR 1 and PAR 2, were analyzed to determine if they are distinct proteins or different conformations of a single polypeptide as has been suggested for other trypanosomatids. Amino acid sequence analysis showed PAR 1 and PAR 2 to be two distinct polypeptides. Antibodies specific against either PAR 1 or PAR 2 were shown to each react with a distinct band in Western blots of paraflagellar isolates of T. cruzi and other trypanosomatids if rigorous protease inhibition was used. The PAR 2 message was isolated and characterized by Northern blot and nucleic acid sequence analysis. Preliminary analysis of the PAR 2 gene indicates that PAR 2 is a member of a multigene family with all members residing on a single chromosome.

Selective aortic arch perfusion during cardiac arrest: a new resuscitation technique

STUDY OBJECTIVES

To demonstrate the technique of selective aortic arch perfusion during cardiac arrest and to observe the hemodynamic effects of volume infusion and aortic epinephrine administration.

DESIGN

Sequential series, nonrandomized, noncontrolled.

TYPE OF PARTICIPANTS

Fourteen mongrel dogs weighing 21 to 36 kg.

INTERVENTIONS

Animals had midaortic arch pressure, right atrial pressure, and descending aortic arch balloon occlusion catheters placed. After ten minutes of ventricular fibrillation, balloon inflation and aortic arch infusions were initiated as follows: group 1 (six), 30 mL/kg/min of 0.9% NaCl for two minutes; group 2 (four), 30 mL/kg/min of oxygenated lactated Ringer's with 2 mg/L epinephrine for two minutes, followed by CPR; and group 3 (four), 20 mL/kg/min of oxygenated perfluorochemicals with 4 mg/L epinephrine for one minute, then CPR.

MEASUREMENTS AND MAIN RESULTS

Midaortic arch pressure, right atrial pressure, and coronary perfusion pressure each rose significantly in all groups. Midaortic arch pressure and coronary perfusion pressure increases were greater in groups 2 and 3 than in group 1. In groups 1 and 2, right atrial pressure increases at end-selective aortic arch perfusion were excessive as midaortic arch pressure and right atrial pressure increased linearly and similarly after 20 to 30 seconds. In groups 2 and 3, CPR-diastolic midaortic arch pressure and coronary perfusion pressure after selective aortic arch perfusion were good and similar to midaortic arch pressure and coronary perfusion pressure at end-selective aortic arch perfusion.

CONCLUSION

Selective aortic arch perfusion is technically feasible, but excessive right atrial pressure increases limit maximal infusion rates and volumes. Selective aortic arch perfusion infusates with epinephrine produce greater midaortic arch pressure and coronary perfusion pressure during infusion than infusate without epinephrine. Controlled studies are needed to determine if selective aortic arch perfusion improves resuscitation outcome.

The non-dosage compensated LSP1-alpha gene of Drosophila melanogaster lies immediately downstream of the dosage compensated L12 gene

The X-linked gene LSP1-alpha of Drosophila melanogaster, expressed in the third larval instar, does not exhibit dosage compensation at its normal locus but does compensate when it is relocated to ectopic sites on the X chromosome. A transcription unit designated L12, which is active in the second larval instar and capable of encoding a putative protein of 28.5 kDa, lies immediately downstream from LSP1-alpha. We have determined that L12 is dosage compensated by measuring the steady-state level of its transcript in male and female larvae. The difference in response of these two adjacent genes should be taken into consideration when models of the mechanism of dosage compensation are formulated.

Nucleotide sequence and transcription of a trypomastigote surface antigen gene of Trypanosoma cruzi

In previous studies we identified a 500-bp segment of the gene, TSA-1, which encodes an 85-kDa trypomastigote-specific surface antigen of the Peru strain of Trypanosoma cruzi. TSA-1 was shown to be located at a telomeric site and to contain a 27-bp tandem repeat unit within the coding region. This repeat unit defines a discrete subset of a multigene family and places the TSA-1 gene within this subset. In this study, we present the complete nucleotide sequence of the TSA-1 gene from the Peru strain. By homology matrix analysis, fragments of two other trypomastigote specific surface antigen genes, pTt34 and SA85-1.1, are shown to have extensive sequence homology with TSA-1 indicating that these genes are members of the same gene family as TSA-1. The TSA-1 subfamily was also found to be active in two other strains of T. cruzi, one of which contains multiple telomeric members and one of which contains a single non-telomeric member, suggesting that transcription is not necessarily dependent on the gene being located at a telomeric site. Also, while some of the sequences found in this gene family are present in 2 size classes of poly(A)+ RNA, others appear to be restricted to only 1 of the 2 RNA classes.

A method of identifying and isolating a unique member of a multigene family: application to a trypanosome surface antigen gene

A chimeric oligonucleotide was constructed using DNA sequences from two distal regions of a cDNA which encodes a major surface antigen (TSA-1) of Trypanosoma cruzi. Conditions were found that allowed the chimeric oligonucleotide to hybridize only to a 5.4 kb EcoRI fragment in a Southern blot of total genomic DNA. The 5.4 kb EcoRI genomic DNA fragment has previously been shown to be located at a telomeric site, thus the studies described here directly demonstrate that the TSA-1 gene is telomeric in location. It is also shown that the chimeric oligonucleotide can be used to selectively identify recombinant lambda phage which harbor the TSA-1 gene using standard library screening procedures. Since these studies demonstrate that a chimeric oligonucleotide can be used to identify in both Southern blots and library screens a single member among the more than sixty members of the TSA-1 gene family, it seems likely that chimeric oligonucleotides may be of general use in studies involving repetitive DNA sequence families.

Trypanosoma cruzi: identification of a surface antigen restricted to the flagellar region of the infective form of the parasite

A hybridoma cell line was derived from spleen cells of B6D2 mice infected with the Peru strain of Trypanosoma cruzi. The monoclonal antibody produced by this hybridoma, designated mAb20H1, reacts exclusively with molecular components of trypomastigotes, the infective form of the parasite. The results of indirect immunofluorescence and of immunoelectron microscopy with gold-tagged antibodies indicate that the 20H1 antigen is restricted to the surface of the part of the flagellum in contact with the cell body and to the surface of the cell body in the immediate vicinity of this organelle. Western blot analysis showed that the 20H1 antigen consists of four to five different molecules with sizes between 34 and 41 kDa, and that these molecules are glycoproteins with affinity for concanavalin A. In other strains of T. cruzi, mAb20H1 reacts with glycoproteins with apparent sizes that range between 37 and 43 kDa in the CL, Esmeraldo and Y strains, and between 41 and 45 kDa in the Silvio strain.

The 85-kd surface antigen gene of Trypanosoma cruzi is telomeric and a member of a multigene family

In previous studies we identified a 500 bp DNA fragment from the genome of Trypanosoma cruzi which encoded epitopes present in an 85 kd trypomastigote-specific surface antigen. A unique feature of this DNA insert was the presence of a 27 bp tandem repeat unit within the putative coding region. The findings presented here show that the gene which encodes this particular surface protein is a member of a multigene family, and that the 27 bp repeat unit defines a subset of this family. Only four separate members of the family contain sequences homologous to the 27 bp repeat unit. Of these, three have been cloned and shown by direct nucleotide sequence analysis not to contain the original 500 bp fragment. By restriction enzyme analysis, the 500 bp fragment is inferred to be present in a 5.4 kb EcoRI genomic DNA fragment that is refractory to isolation by standard cloning procedures. Preferential sensitivity of this fragment to digestion with Bal31 nuclease indicates that it is likely to be telomeric, thus explaining the inability to obtain it in several different recombinant DNA libraries. In order to determine which of the four members were transcribed, 26 cDNA recombinants having sequence homology with the 27 bp repeat were examined. Restriction enzyme maps and nucleotide sequence analysis of these cDNAs indicate that transcription occurs almost exclusively from the telomeric member of the family.

Determination of viridans streptococci surface lipoteichoic acid by enzyme linked immune sorbent assay

An enzyme linked immune sorbent assay (ELISA) was developed to measure bacterial surface lipoteichoic acid (LTA). Numerous strains of oral streptococci belonging to the 'viridans' group were examined on three separate occasions. The results show that, under these cultural conditions, oral streptococci do not normally express LTA on the cell surface. Occasionally strains produced amounts of LTA detectable using the ELISA but this was not a reproducible phenomenon.

The LSP1-alpha gene of Drosophila melanogaster exhibits dosage compensation when it is relocated to a different site on the X chromosome

The LSP1-alpha gene of Drosophila melanogaster is located on the X chromosome at 11B yet is not dosage compensated. In order to determine if this gene is inherently incapable of dosage compensation or if it does not compensate because the appropriate regulatory cis-acting sequences are absent from its chromosomal domain, we have undertaken to relocate it to ectopic sites on the X chromosome. To differentiate between the transcripts produced by the transduced gene and those produced by the indigenous gene, we inserted a 500-bp sequence of mouse DNA into the LSP1-alpha clone prior to using it for transformation. Our results show that the LSP1-alpha gene exhibits equivalent levels of transcripts in the two sexes when it is relocated to either an autosomal site or to an ectopic site on the X chromosome. We conclude that the LSP1-alpha gene is capable of dosage compensation.

Cloning and dosage compensation of the 6-phosphogluconate dehydrogenase gene (Pgd+) of Drosophila melanogaster

Using a heterologous rat cDNA probe, we have identified a 14.7 kbp Drosophila melanogaster genomic clone containing the X-linked gene Pgd+, which encodes the enzyme 6-phosphogluconate dehydrogenase (6PGD). We used in situ hybridization to larval polytene chromosomes, a somatic transient expression assay for enzyme activity, and the rescue of the lethal Pgd- phenotype by germline transformation to verify the identity of the gene. A 7.4 kbp fragment including the gene and approximately 1.2 kbp of upstream and 1.8 kbp of downstream sequences was relocated to autosomal ectopic sites by germline transformation; this transduced gene exhibits levels of enhanced activity in males comparable to those of the indigenous gene at its normal X chromosome locus. We conclude that the sequences responsible for dosage compensation of Pgd+ are included in this fragment.

Inhibition of adhesion of viridans streptococci to fibronectin-coated hydroxyapatite beads by lipoteichoic acid

Fibronectin-coated hydroxyapatite (FnHA) beads were used in a model adhesion assay to isolate the lipoteichoic acid (LTA) mediated adhesion of oral streptococci. Representative strains of the commonly isolated viridans streptococci were incubated with FnHA beads in the presence and absence of exogenous LTA. The LTA inhibited the adhesion of all strains to a greater or lesser extent, but only a very few strains were inhibited by more than 90%. Strains of Streptococcus sanguis Type II and Streptococcus mitis which synthesize an amphiphile other than LTA were also inhibited. The findings provided circumstantial evidence for the involvement of LTA in the adhesion of this group of oral bacteria.