Induction of specific cell-mediated immunity in mice by oral immunization with Salmonella expressing Onchocerca volvulus glutathione S-transferase

Cellular and humoral immune responses of mice to Onchocerca volvulus glutathione S-transferase (OvGST) presented via in vivo expression in attenuated Salmonella typhimurium were examined and compared with the same antigen administered by subcutaneous injection with Freund's adjuvant. After infection with recombinant S. typhimurium, maximal numbers of bacteria were recovered from the mesenteric lymph nodes and spleens during the second week postinfection. By weeks 3-4, bacteria were absent from these tissues. Splenocytes from mice infected with S. typhimurium expressing OvGST showed significant and specific proliferative responses to OvGST, whereas the non-recombinant S. typhimurium controls and those which received the antigen by subcutaneous injection with Freund's adjuvant did not. Mice infected with recombinant S. typhimurium had elevated IFN-gamma levels over non-recombinant S. typhimurium and placebo controls. but IL-4 and IL-5 levels were low and did not differ significantly between these groups. Antibody responses to OvGST antigen expressed by a recombinant Salmonella vaccine or delivered in a purified form with Freund's adjuvant were moderate to high. These data suggest that Salmonella can be used as a vaccine delivery vector that induces specific cellular and humoral immune responses to Onchocerca volvulus antigens. This is the first report to describe the successful application of a filarial antigen in a live-vector delivery system as well as the first recombinant based filarial vaccine to elicit a cellular immune response similar to that described for putative immune endemics.

Use of a PCR assay for diagnosing African trypanosomiasis of the CNS: a case report

The diagnosis of African trypanosomiasis is parasitologic and often can be difficult, especially in patients infected with Trypanosoma brucei gambiense, the cause of West African sleeping sickness. In the United States imported cases of sleeping sickness are rare, and most occur in tourists returning from East African game parks rather than among immigrants. I report here the use of a T. brucei specific PCR assay in a West African immigrant who presented with neurological symptoms more than 12 years after he had last been in Africa. The patient's historical and physical findings, as well as abnormal cerebrospinal fluid (CSF) parameters, suggested a diagnosis of sleeping sickness. The diagnosis was confirmed when the PCR assay demonstrated the presence of parasite DNA in CSF and blood. Several months after curative therapy the CSF continued to be positive by PCR. These findings suggest that the PCR assay may be useful for sensitive and specific diagnosis of sleeping sickness, but that it may not be helpful for assessing the effect of drug treatment.

Seroepidemiology of Trypanosoma cruzi, etiologic agent of Chagas' disease, in US blood donors

A comprehensive seroepidemiologic study was conducted in two Red Cross regions (Los Angeles and Miami) to determine the prevalence of Trypanosoma cruzi antibodies in at-risk blood donors, to identify additional risk factors, and to assess the likelihood of transmitting T. cruzi by transfusion. At-risk and control donors were stratified by a broad risk question, tested for T. cruzi antibodies, and if confirmed as seropositive, enrolled in case-control and lookback investigations. A total of 299,398 donors were queried; 23,978 at-risk and 25,587 control donations were tested, and T. cruzi antibodies were confirmed in 34 donors (33 and 1, respectively). Seropositive donors shared one risk factor; birth/extensive time in a T. cruzi-endemic area. Lookback studies identified 11 recipients, all negative for T. cruzi antibodies. Screening strategies that use a question are unlikely to identify all seropositive donors. The lack of definitive data on the risk of transmission by transfusion indicates additional studies of donors and recipients are needed.

Specific antibodies to Trypanosoma cruzi among blood donors in Los Angeles, California

BACKGROUND

Trypanosoma cruzi, the cause of Chagas' disease, is often transmitted by transfusion in Latin America. Previous studies showed that at least 1 in 1000 eligible blood donors at the Los Angeles County+University of Southern California (LAC+USC) Medical Center Blood Bank had specific antibodies to T. cruzi. In June 1993, serologic screening of prospective allogeneic donors at epidemiologic risk for T. cruzi infection was begun voluntarily.

STUDY DESIGN AND METHODS

The risk of T. cruzi infection in all eligible donors was assessed by questionnaire. At-risk donors were screened serologically for antibodies to T. cruzi with an enzyme immunoassay, and confirmatory testing was done with a radioimmunoprecipitation assay.

RESULTS

During the 29-month study period 1311 (39.5%) of 3320 donors were judged to be at risk for T. cruzi infection. Seven donors (1/475) were reactive by an enzyme immunoassay, and six of these seven (1/ 553) were positive in a radioimmunoprecipitation assay. All radioimmunoprecipitation assay-positive donors had been born in countries in which Chagas' disease is endemic. One person in this group had received a transfusion in his homeland.

CONCLUSION

These results demonstrate that a substantive proportion of eligible blood donors at our institution have antibodies specific for T. cruzi and that a commercially available assay can be used to detect these antibodies. Our data suggest that the risk of transmission of T. cruzi by transfusion could be eliminated by serologic testing limited to persons born in or transfused in countries in which Chagas' disease is endemic.

Asymptomatic perianal shedding of herpes simplex virus in patients with acquired immunodeficiency syndrome

OBJECTIVE

To determine the frequency of asymptomatic perianal shedding of herpes simplex virus (HSV) in adult patients with acquired immunodeficiency syndrome (AIDS).

DESIGN

Cross-sectional study.

SETTING

A 1000-bed, state-supported hospital in Brazil that provides comprehensive health care.

PATIENTS

Eighty-two consecutively hospitalized patients with AIDS (Centers for Disease Control and Prevention class C).

MAIN OUTCOME MEASUREMENT

Specimens for HSV culture were obtained with premoistened swabs of the perianal region at approximately 7-day intervals during the hospitalization of each patient. After the specimens were inoculated into cultures of human foreskin and Vero cells, supernatants of cultures showing the cytopathic effect characteristic of HSV infection were tested for virus in a confirmatory immunoenzymatic assay. Typing of HSV was performed by polymerase chain reaction amplification of HSV-1- and HSV-2-specific DNA polymerase sequences.

RESULTS

On early into the study, 12 (15%) of 82 patients had perianal ulceration and 70 did not. None of the patients in the latter group developed perianal ulcers during the study period, but HSV was isolated at least once from 17 (24%) of them. Nine of the 17 asymptomatic perianal shedders had a mean of 3 perianal swabs collected before the first HSV isolation, and 11 (65%) of 17 had a total of 18 perianal swabs collected 8 to 62 days after the HSV isolation. All postpositive samples were negative for HSV except 1 obtained from a patient 13 days after the first positive sample. Twelve of the 17 asymptomatic perianal shedders of HSV were followed up clinically for 8 to 62 days after the first episode of shedding and none developed perianal ulceration.

CONCLUSIONS

We conclude that asymptomatic perianal shedding of HSV is common in patients with AIDS, even among those without a history of perianal HSV lesions. This shedding appears to be short-lived, intermittent, and not associated with early subsequent development of perianal ulcers. These findings present a new perspective on the natural course of perianal HSV infection in patients with AIDS.

Use of the polymerase chain reaction for detecting Trypanosoma cruzi in triatomine vectors

Determination of the rate of Trypanosoma cruzi infection in its triatomine vectors is an element in control programmes directed at reducing transmission of the organism to humans. Traditionally, T. cruzi has been detected in these insects by microscopical examination of intestinal contents or excreta. The sensitivity of this laborious process has not been defined because of the lack of a bench-mark method against which microscopical examination could be compared. The purpose of this study was to compare the sensitivity of a polymerase chain reaction (PCR) assay with that of microscopical examination for detecting T. cruzi in Triatoma infestans nymphs that had fed on patients with chronic Chagas disease. To this end, we analysed 54 pairs of samples, each containing 2 groups of 10 insects, obtained by feedings on 19 patients with chronic T. cruzi infection, 17 of whom were fed upon 3 times. One group of insects in each pair was analysed by PCR and the other by microscopical examination of excreta. Overall, the PCR assay gave positive results in 32 of 54 groups of insects examined (59%), whereas only 7 of 54 groups (13%) were positive by microscopical examination (P = 0.038). These results demonstrate that the PCR assay is significantly more sensitive for the detection of T. cruzi in triatomine vectors than is microscopical examination, and suggest that the PCR assay could be a useful tool in epizootiological studies.

American trypanosomiasis (Chagas' disease)

Gastrointestinal dysfunction is a major problem for many patients with chronic Chagas' disease, as are cardiac dysrhythmias and cardiomyopathy. The underlying anatomic abnormality in these patients is a denervation of the gastrointestinal tract. This process of nerve destruction usually develops insidiously over many years, and it is highly variable in terms of its extent in individual patients as well as in the segments of the gastrointestinal tract that are most affected. Megaesophagus is the most common manifestation of gastrointestinal Chagas disease, and mechanical dilation of the esophageal sphincter or surgery in advanced cases usually give satisfactory relief of symptoms. Megacolon, particularly of the sigmoid segment, is also common in patients with chronic T. cruzi infections, and its presence can be complicated by fecal impaction or sigmoid volvulus. Patients with advanced megacolon who have resections of the sigmoid colon and most of the rectum generally do well postoperatively.

Comparison of PCR and microscopic methods for detecting Trypanosoma cruzi

The diagnosis of acute infection with Trypanosoma cruzi, the protozoan parasite that causes Chagas' disease, is generally made by detecting parasites by microscopic examination of fresh blood. Although highly specific, this approach often lacks sensitivity. Several years ago, PCR assays for the detection of T. cruzi were described, but the sensitivities and specificities of these tests have not yet been defined precisely. In the present study, we first compared the sensitivities of PCR methods that differ in sample processing as well as in the target sequences that are amplified. Then, we challenged eight mice with T. cruzi, and on 31 days over a 380-day period, we compared the ability of the PCR method with the highest sensitivity to detect parasites in blood with that of microscopic examination. During the acute phase of the infections, parasites were detected on average 3.9 days earlier by the PCR method than by microscopy. Furthermore, the infected mice were consistently positive by the PCR method during the chronic phase, while parasites were intermittently detected by microscopic examination during that period. Overall, among the 248 comparisons, in 84 the PCR method was positive and no parasites were seen by microscopic examination, whereas the reverse was true in only 1 case, a difference that is highly significant. These findings suggest that this approach should be in patients suspected of having acute Chagas' disease. Moreover, the higher sensitivity of the PCR method observed in both the acute and chronic phases of the T. cruzi infections in the mice that we studied indicates that this approach should be useful in evaluating experimental drugs in T. cruzi-infected laboratory animals.

Postmortem diagnosis of autochthonous acute chagasic myocarditis by polymerase chain reaction amplification of a species-specific DNA sequence of Trypanosoma cruzi

We report a fatal case of vector-transmitted acute Chagas' myocarditis in a seven-month-old child in south Texas. This diagnosis was not suspected during the three days of hospitalization that preceded the child's death, which was caused by heart failure. A diagnosis of acute myocarditis, probably of viral origin, was listed as the cause of death after cardiac tissue was examined microscopically at autopsy. One year after the death of the patient, a diagnosis of Trypanosoma cruzi myocarditis, based solely on morphological grounds, was made after newly prepared slides of cardiac tissue were examined. Seven years later, we confirmed the diagnosis of T. cruzi infection by using the polymerase chain reaction to amplify a species-specific genomic repetitive DNA sequence of the parasite from fixed cardiac tissue.

Risk factors for Trypanosoma cruzi infection in California blood donors

BACKGROUND

Trypanosoma cruzi, the protozoan parasite that causes Chagas'disease, is endemic in Central and South America and in Mexico. Risk of infection is related to exposure to insects harboring T. cruzi or to the transfusion of blood from an infected donor. Large numbers of immigrants from endemic areas reside in California, but the frequency with which persons at risk for T. cruzi contribute to the blood supply there is not known.

STUDY DESIGN AND METHODS

A questionnaire was used to survey donors in 18 California donor centers for risk factors for T. cruzi infection.

RESULTS

Otherwise eligible allogeneic blood donors (n = 17,521) completed questionnaires. Of this group, 427 (2.4%) had lived in endemic areas for more than 1 year, and 39 of these donors had lived in dwellings with mud walls or thatched roofs. Sixteen donors had received transfusions in endemic areas. Six donors gave a history of Chagas' disease. Fifty-seven donors (0.33% of total) had at least one risk factor for T. cruzi infection. Donors at risk for T. cruzi were found in all 18 centers studied, at a median prevalence of 1 per 340 donors.

CONCLUSION

Donors at risk for T. cruzi are contributing to the blood supply throughout California. Further consideration should be given to donor screening for this transfusion-transmissible infection.

Maxicircle genomic organization and editing of an ATPase subunit 6 RNA in Trypanosoma cruzi

The DNA sequence of a 5736-nucleotide (nt) Trypanosoma cruzi maxicircle fragment was determined. Sequence comparisons indicate that its 5' terminus is the homologue of the downstream portion of the NADH dehydrogenase subunit 7 gene and that its 3' region is homologous to the maxicircle unidentified reading frame II gene. The region between these two gene segments contains six additional genes that encode mitochondrial proteins, including ATPase subunit 6 (A6). Comparison of the A6 maxicircle DNA sequence with that of an A6 cDNA indicates that the A6 RNA is extensively edited throughout its length. A 49-nt sequence that could serve as template for transcription of a guide RNA for editing a segment of the A6 RNA was found in one of 24 minicircle variable regions sequenced. Moreover, the presence of an RNA having this sequence was demonstrated in an RNAse protection assay. This is the first identification of a guide RNA template in a T. cruzi minicircle. Taken together, our findings suggest that T. cruzi and Trypanosoma brucei brucei are phylogenetically closer to each other than they are to Leishmania tarentolae, despite the relative similarity of the life cycles of the latter and T. cruzi.

Trypanosoma cruzi: interruption of both alleles of a gene encoding a protein containing 14-amino-acid repeats by targeted insertion of NEOr and HYGr

In Trypanosoma cruzi approximately 90% of the 121- and 176-kDa cytoskeletal proteins encoded by the two alleles of the TCR27 gene is composed of 14-amino-acid repeats. To gain insight into the function of the TCR27 proteins we replaced the corresponding regions of 42-nucleotide repeats in the two alleles with the NEOr and HYGr genes. Analyses of DNAs and RNAs from four clones resistant to both G418, a neomycin analogue, and hygromycin showed that in both cases the repetitive regions had in fact been deleted. In addition, the absence of expression of the 14-amino-acid repeats was confirmed in Western blots. In axenic cultures growth rates of the morphologically unchanged, doubly resistant organisms were not different from those of wild-type parasites. However, the doubly resistant organisms proliferated more slowly in cultured mammalian cells than did wild-type parasites. These findings indicate that the absence of the TCR27 repetitive regions is detrimental, but not fatal, to the parasites.

Post-transcriptional elements regulating expression of mRNAs from the amastin/tuzin gene cluster of Trypanosoma cruzi

The genome of Trypanosoma cruzi contains tandemly arrayed copies of the gene encoding amastin, an abundant protein on the surface of the amastigote stage of the parasite. The transcription rate of the amastin genes is the same in the different developmental stages, but the steady state level of the 1.4-kilobase amastin mRNA is 50-85 times higher in amastigotes than in epimastigotes or trypomastigotes (1). Here we show that the amastin genes alternate with genes encoding another protein, called tuzin, whose 1.7-kilobase mRNA is much less abundant in amastigotes. The 3'-untranslated region (UTR) of tuzin mRNA is only a few nucleotides in length or even nonexistent, in contrast with the 630-nucleotide 3'-UTR of amastin mRNA. No promoter elements were found upstream or within the amastin/tuzin gene cluster. However, in amastigotes, the protein synthesis inhibitor cycloheximide caused a 3-fold decrease in amastin mRNA and a 7-fold increase in tuzin mRNA. Furthermore, when the amastin 3'-UTR plus its downstream intergenic region were fused behind the luciferase coding region in a chimeric plasmid for transient transfections, luciferase activity increased 7-fold in amastigotes and decreased 5-fold in epimastigotes. Thus, developmental expression of these alternating genes is regulated by different mechanisms.

Trypanosoma cruzi infection in Walker hounds from Virginia

Trypanosomiasis has been reported in dogs from Texas, Oklahoma, Louisiana, and South Carolina. We describe the first isolation and characterization of Trypanosoma cruzi from a Walker Hound pup in Virginia that also had postvaccinal distemper. The mother of the pup and 7 of its 8 siblings also were found to be infected with T cruzi, suggesting that the parasite had been transmitted transplacentally or through lactation. Parasitologic, serologic, histologic, and molecular methods were used to establish the diagnosis of T cruzi infection in these dogs. In a serologic survey of 12 dogs (including the sire of the pups) from the area in which the index case occurred, none were found to have antibodies to T cruzi. However, 2 of a further 52 dogs from different areas (to the index case), but in the same county, were seropositive to T cruzi. These findings indicate that canine trypanosomiasis is present in an area of the United States not previously known to be enzootic.

Repetitive protein antigens of Trypanosoma cruzi have diverse intracellular locations

We previously identified by immunoscreening Trypanosoma cruzi cDNA libraries a group of proteins containing long stretches of tandem repeats. The goal of the current project was to gain insight into the functions of these proteins through ultrastructural analyses consisting of western blotting and electron microscopic localization studies. By comparing western blots of total parasite lysate and different fractions of T. cruzi, we found that 3 of the repetitive antigens are exclusively associated with the parasite membrane, or cytoskeleton, or both. One of the 4 repetitive antigens studied has some association with the membrane or cytoskeleton but also appears to be free in the cytosol. In immunoelectron microscopic studies, the 4 repetitive antigens were detected in different intracellular locations. One of the proteins is located between the flagellum and parasite body, the second has a nuclear distribution, the third is associated with the cell membrane, and the fourth is dispersed throughout the cytoskeletal network. These findings suggest that despite the general structure similarities of these repetitive proteins, they may serve different cellular functions.

Characterization of a Trypanosoma cruzi poly(A)-binding protein and its genes

We have characterized the biochemical properties of a 66-kDa poly(A)-binding protein (PABP1) in the protozoan Trypanosoma cruzi and isolated two classes of cDNAs encoding the protein. In concordance, Southern blots showed the presence of 2 gene copies. The two cDNA classes differ in the length of adenosine-rich segments in the 5' untranslated region and in point changes scattered throughout the sequence, but their 1650-bp open reading frames encode identical proteins. A single mRNA of 5.5 kb was detected, indicating that the noncoding regions are unusually long. Both the mRNA and the protein are constitutively expressed in all stages of T. cruzi life cycle. The biochemical properties and sequence comparisons show that the T. cruzi PABP1 is similar to the PABP1 of other eukaryotic organisms. These results indicate that PABP1 has been conserved throughout eukaryotic evolution.

A differentially expressed gene family encoding "amastin," a surface protein of Trypanosoma cruzi amastigotes

A new family of closely related glycoproteins, collectively called amastins, has been found on the surface of the amastigote form of Trypanosoma cruzi. The gene family encoding these amastigote-specific proteins was identified by differentially screening an amastigote cDNA library with reverse transcribed poly(A)+ RNA from amastigote and epimastigote stages of the parasite. Amastins are encoded by eight or more tandem genes, at least five of which are distinguished by nucleotide point changes. The 1.4-kilobase amastin mRNAs are 50 times more abundant in amastigotes than in epimastigotes or trypomastigotes. The amastin genes are transcribed to an equal extent in both amastigotes and epimastigotes, indicating that the stage-specific amastin mRNA levels are determined by a post-transcriptional mechanism. Sequence determination of full-length cDNAs reveals an open reading frame encoding 174 amino acids and a 700-base pair 3'-untranslated region. Nascent amastins contain four distinct hydrophobic regions of 20-30 amino acids each, 2 at internal locations and 1 each at the N and C termini.

Transcription and editing of cytochrome oxidase II RNAs in Trypanosoma cruzi

The cytochrome oxidase subunit II (COII) gene is one of the maxicircle cryptogenes of kinetoplastids whose primary transcripts are sometimes modified by RNA editing to produce mature mRNAs. We determined the sequence of the COII gene in three strains of Trypanosoma cruzi (Y, Corpus Christi, and Tulahuén) and examined its developmental expression. Comparison of the RNA and DNA sequences encoding COII indicated that in the three strains of T. cruzi, four uridines are inserted in the pre-mRNA at the same positions as they are in the COII pre-mRNAs of Trypanosoma brucei, Leishmania tarentolae, and Crithidia fasciculata. The putative guide RNA (gRNA) sequence that serves as a template for the four uridine insertions is located in the 3'-untranslated region of the T. cruzi COII mRNA. Analysis of editing intermediates demonstrates that the COII gRNA remains attached to the pre-mRNA while participating in the formation of chimeric RNAs. Northern blots used to investigate stage-specific expression of the COII gene revealed RNAs of 800 and 900 nucleotides, similar in size to those present in T. brucei. In contrast to the differential expression observed in T. brucei, no difference occurs between the COII mRNA levels of insect and mammalian stages of T. cruzi.

Characterization of kinetoplast DNA minicircles in Trypanosoma rangeli

Kinetoplast DNA, the mitochondrial DNA of kinetoplastid protozoans, is a network of interlocked minicircles and maxicircles. We analyzed the sequence organization of minicircle DNAs in the El Tocuyo strain and the San Augustin clone B6 of Trypanosoma rangeli. The frequencies of different minicircle types, as defined by the number of 136-bp conserved regions (CRs), are different in the two strains. About half of the 1.7-kb T. rangeli El Tocuyo minicircles have 1 CR and most of the others have 2. In contrast, most of the 1.6-kb T. rangeli San Augustin minicircles have 2 CRs, while some have four. The CR contains a replication origin at one end and is conserved both within and between the two strains. Comparisons of the T. rangeli El Tocuyo and T. rangeli San Augustin minicircle CRs with minicircle CRs of other kinetoplastid species reveal that they are most similar to those of Trypanosoma cruzi.

Kinetic analysis of antigen-specific immune responses in resistant and susceptible mice during infection with Trypanosoma cruzi

The Tulahuén strain of Trypanosoma cruzi has been shown previously to cause higher parasitemias and greater mortality in BALB/c mice compared with C57BL6/J mice. The goal of our study was to determine whether different cytokine responses to parasite Ag during T. cruzi infection correlate with the susceptible and resistant phenotypes identified in these mice. At several time points after initial infection with insect-derived metacyclic trypomastigotes, lymph node and spleen cell suspensions were prepared from animals of each mouse strain. These lymphocyte suspensions were stimulated with Ag prepared from cultured parasites and the production of IFN-gamma, IL-4, IL-2, and IL-5 was measured. Lymphocytes from C57BL6/J mice produced 10-fold more IFN-gamma than BALB/c lymphocytes. However, this enhanced response occurred only for a limited time preceding peak parasitemias. Ag-induced secretion of IL-4 from BALB/c lymphocytes was detectable by 2 wk of infection and increased during the 2nd and 3rd mo of infection. Most C57BL6/J culture supernatants did not contain measurable levels of IL-4. Lymphocytes from both murine strains produced levels of IL-2 and IL-5 indistinguishable from uninfected controls. These results indicate that increased numbers or potency of lymphocytes that produce Ag-specific IFN-gamma responses are present in resistant mice during T. cruzi infection. This phenomenon may be responsible for the lower parasitemias seen in C57BL6/J mice. However, even these relatively resistant mice become chronically infected with T. cruzi, and spleen cells from infected mice can suppress IFN-gamma induced by heterologous Ag. Our data suggest that IL-4 production is a marker for the T. cruzi susceptible phenotype. Differential production of IL-2 or IL-5 was not found, suggesting that these cytokines are not important factors in T. cruzi resistance or susceptibility.

Kinetic analysis of antigen-specific immune responses in resistant and susceptible mice during infection with Trypanosoma cruzi

The Tulahuén strain of Trypanosoma cruzi has been shown previously to cause higher parasitemias and greater mortality in BALB/c mice compared with C57BL6/J mice. The goal of our study was to determine whether different cytokine responses to parasite Ag during T. cruzi infection correlate with the susceptible and resistant phenotypes identified in these mice. At several time points after initial infection with insect-derived metacyclic trypomastigotes, lymph node and spleen cell suspensions were prepared from animals of each mouse strain. These lymphocyte suspensions were stimulated with Ag prepared from cultured parasites and the production of IFN-gamma, IL-4, IL-2, and IL-5 was measured. Lymphocytes from C57BL6/J mice produced 10-fold more IFN-gamma than BALB/c lymphocytes. However, this enhanced response occurred only for a limited time preceding peak parasitemias. Ag-induced secretion of IL-4 from BALB/c lymphocytes was detectable by 2 wk of infection and increased during the 2nd and 3rd mo of infection. Most C57BL6/J culture supernatants did not contain measurable levels of IL-4. Lymphocytes from both murine strains produced levels of IL-2 and IL-5 indistinguishable from uninfected controls. These results indicate that increased numbers or potency of lymphocytes that produce Ag-specific IFN-gamma responses are present in resistant mice during T. cruzi infection. This phenomenon may be responsible for the lower parasitemias seen in C57BL6/J mice. However, even these relatively resistant mice become chronically infected with T. cruzi, and spleen cells from infected mice can suppress IFN-gamma induced by heterologous Ag. Our data suggest that IL-4 production is a marker for the T. cruzi susceptible phenotype. Differential production of IL-2 or IL-5 was not found, suggesting that these cytokines are not important factors in T. cruzi resistance or susceptibility.

Chagas disease. American trypanosomiasis

Chagas disease, caused by the protozoan parasite, Trypanosoma cruzi, is a major source of morbidity and death in Latin America. Many infected immigrants from that region now reside in the United States, posing a risk of transfusion-associated transmission of the organism. Serologic testing is the cornerstone of diagnosing chronic T. cruzi infections, and improved assays are needed. Drug treatment is problematic because the two available drugs can have severe side effects and lack efficacy. T. cruzi infection can be particularly severe in immunosuppressed patients.