IgM and antibody measurement in the diagnosis and management of Gambian trypanosomiasis

IgM, lgG and IL-6 profiles in the Trypanosoma brucei brucei monkey model of human African trypanosomiasis

Human African trypanosomiasis (HAT) patients manifest immunological profiles, whose variations over time can be used to indicate disease progression. However, monitoring of these biomarkers in human patients is beset by several limitations which can be offset by using chronic animal models. A recent improved monkey model of HAT using a Trypanosoma brucei brucei isolate has been developed but the immunological profile has not been elucidated. The objectives of the current study was to determine the IgM, IgG and IL-6 profiles in blood and cerebrospinal fluid (CSF) in vervet monkeys infected with T. b. brucei. Three vervet monkeys were infected intravenously with 10⁵T. b. brucei, monitored for disease development and subsequently treated 28days post infection (dpi) sub-curatively using diminazene aceturate (DA) to induce late stage disease and curatively treated with melarsoprol (Mel B) at 119 dpi, respectively. Matched serum and cerebrospinal fluid (CSF) samples were obtained at regular intervals and immunospecific IgM, immunoglobulin G (IgG) were quantified by ELISA while IL-6 was assayed using a cytometric bead array (CBA) kit. Results showed that following infection, CSF IgM, IgG, IL-6 and serum IL-6 were significantly (p<0.05) elevated with peak levels coinciding with relapse parasitaemia. The IgG levels increased to reach OD peak levels of 0.442±0.5 at 126 dpi. After curative treatment with MelB, the serum IgM and Ig G levels fell rapidly to attain pre-infection levels within 35 and 49days, respectively. This shows that the profile of these immunoglobulins can be used as an indicator of curative treatment. CSF IL-6 concentrations of infected vervet monkeys showed no significant change (P>0.05) between infection and 35 dpi but levels increased significantly (P<0.05) with the highest level of 55.53pg/ml recorded at112 dpi. IL-6 elevation from 35 dpi may be indicative of parasite neuroinvasion hence can be used as possible candidate marker for late stage disease in the monkey model. Further, the marker can also be used in conjunction with IgG and IgM as markers for development of test of cure for HAT.

Human African trypanosomiasis in non-endemic countries

Human African trypanosomiasis (HAT) or sleeping sickness is a parasitic disease, acquired by the bite of an infected tsetse fly. In non-endemic countries HAT is rare, and therefore the diagnosis may be delayed leading to potentially fatal consequences. In this article the clinical presentation, diagnosis and treatment of the two forms of HAT are outlined. Rhodesiense HAT is an acute illness that presents in tourists who have recently visited game parks in Eastern or Southern Africa, whereas Gambiense HAT has a more chronic clinical course, in individuals from West or Central Africa.

Murine Models for Trypanosoma brucei gambiense disease progression--from silent to chronic infections and early brain tropism

Background

Human African trypanosomiasis (HAT) caused by Trypanosoma brucei gambiense remains highly prevalent in west and central Africa and is lethal if left untreated. The major problem is that the disease often evolves toward chronic or asymptomatic forms with low and fluctuating parasitaemia producing apparently aparasitaemic serological suspects who remain untreated because of the toxicity of the chemotherapy. Whether the different types of infections are due to host or parasite factors has been difficult to address, since T. b. gambiense isolated from patients is often not infectious in rodents thus limiting the variety of isolates.

Methodology/Principal findings

T. b. gambiense parasites were outgrown directly from the cerebrospinal fluid of infected patients by in vitro culture and analyzed for their molecular polymorphisms. Experimental murine infections showed that these isolates could be clustered into three groups with different characteristics regarding their in vivo infection properties, immune response and capacity for brain invasion. The first isolate induced a classical chronic infection with a fluctuating blood parasitaemia, an invasion of the central nervous system (CNS), a trypanosome specific-antibody response and death of the animals within 6–8 months. The second group induced a sub-chronic infection resulting in a single wave of parasitaemia after infection, followed by a low parasitaemia with no parasites detected by microscope observations of blood but detected by PCR, and the presence of a specific antibody response. The third isolate induced a silent infection characterised by the absence of microscopically detectable parasites throughout, but infection was detectable by PCR during the whole course of infection. Additionally, specific antibodies were barely detectable when mice were infected with a low number of this group of parasites. In both sub-chronic and chronic infections, most of the mice survived more than one year without major clinical symptoms despite an early dissemination and growth of the parasites in different organs including the CNS, as demonstrated by bioluminescent imaging.

Conclusions/Significance

Whereas trypanosome characterisation assigned all these isolates to the homogeneous Group I of T. b. gambiense, they clearly induce very different infections in mice thus mimicking the broad clinical diversity observed in HAT due to T. b. gambiense. Therefore, these murine models will be very useful for the understanding of different aspects of the physiopathology of HAT and for the development of new diagnostic tools and drugs.

Trypanosoma brucei gambiense is responsible for more than 90% of reported cases of human African trypanosomosis (HAT). Infection can last for months or even years without major signs or symptoms of infection, but if left untreated, sleeping sickness is always fatal. In the present study, different T. b. gambiense field isolates from the cerebrospinal fluid of patients with HAT were adapted to growth in vitro. These isolates belong to the homogeneous Group 1 of T. b. gambiense, which is known to induce a chronic infection in humans. In spite of this, these isolates induced infections ranging from chronic to silent in mice, with variations in parasitaemia, mouse lifespan, their ability to invade the CNS and to elicit specific immune responses. In addition, during infection, an unexpected early tropism for the brain as well as the spleen and lungs was observed using bioluminescence analysis. The murine models presented in this work provide new insights into our understanding of HAT and allow further studies of parasite tropism during infection, which will be very useful for the treatment and the diagnosis of the disease.

Immunospecific immunoglobulins and IL-10 as markers for Trypanosoma brucei rhodesiense late stage disease in experimentally infected vervet monkeys

OBJECTIVE

To determine the usefulness of IL-10 and immunoglobulin M (IgM) as biomarkers for staging HAT in vervet monkeys, a useful pathogenesis model for humans.

METHODS

Vervet monkeys were infected with Trypanosoma brucei rhodesiense and subsequently given sub-curative and curative treatment 28 and 140 days post-infection (dpi) respectively. Matched serum and CSF samples were obtained at regular intervals and immunospecific IgM, immunoglobulin G (IgG) and IL-10 were quantified by ELISA.

RESULTS

There was no detectable immunospecific IgM and IgG in the CSF before 49 dpi. CSF IgM and IgG and serum IgM were significantly elevated with peak levels coinciding with meningoencephalitis 98 dpi. The serum IL-10 was upregulated in both early and late disease stage, coinciding with primary and relapse parasitaemia respectively. CSF white cell counts (CSF WCC) were elevated progressively till curative treatment was given. After curative treatment, there was rapid and significant drop in serum IgM and IL-10 concentration as well as CSF WCC. However, the CSF IgM and IgG remained detectable to the end of the study.

CONCLUSIONS

Serum and CSF concentrations of immunospecific IgM and CSF IgG changes followed a pattern that mimics the progression of the disease and may present reliable and useful biomarkers of the disease stage. Due to rapid decline, serum IgM and IL-10 are, additionally, potential biomarkers of the success of chemotherapy.

Novel markers for treatment outcome in late-stage Trypanosoma brucei gambiense trypanosomiasis

BACKGROUND

To date, no biological marker for treatment outcome in human African trypanosomiasis (HAT) has been described. The accuracy of biological markers for prediction of treatment outcome of HAT caused by Trypanosoma brucei gambiense was assessed.

METHODS

Cerebrospinal fluid (CSF) white blood cell (WBC) count and immunoglobulin M (IgM), trypanosome-specific antibody, total protein, and interleukin-10 levels were determined before and up to 24 months after treatment of late-stage HAT.

RESULTS

Treatment failure was experienced by 48 of 260 patients. Pretreatment CSF WBC counts > or = 102 cells/microL, IL-10 concentrations > or = 37 pg/mL, LATEX/IgM end titers > or = 1:32, LATEX/T. b. gambiense end titers > or = 1:2, and protein concentrations > or = 674 mg/L were associated with treatment failure. Six months after treatment, patients with CSF WBC counts < or = 5 cells/microL were at low risk of HAT recurrence (negative predictive value, >0.93). After 12 months, the combination of CSF WBC count > or = 8 cells/microL and LATEX/IgM end titer > or = 1:4 predicted treatment failure with 97% specificity and 79% sensitivity. Eighteen months after treatment, each marker accurately predicted treatment outcome. The combination of CSF WBC count > or = 8 cells/microL and LATEX/IgM end titer > or = 1:4 was 100% specific for treatment failure after 18 and 24 months.

CONCLUSIONS

HAT-affected patients with elevated pretreatment CSF levels of WBC, interleukin-10, IgM, trypanosome-specific antibody, and total protein are at risk of treatment failure. Six months after treatment, patients with CSF WBC counts < or = 5 cells/microL can be considered to be cured. The assessment of a combination of CSF WBC count and LATEX/IgM level allowed accurate prediction of outcome beginning at 12 months after treatment, as did each individual marker at 18 months after treatment.

Options for field diagnosis of human african trypanosomiasis

Human African trypanosomiasis (HAT) due to Trypanosoma brucei gambiense or T. b. rhodesiense remains highly prevalent in several rural areas of sub-Saharan Africa and is lethal if left untreated. Therefore, accurate tools are absolutely required for field diagnosis. For T. b. gambiense HAT, highly sensitive tests are available for serological screening but the sensitivity of parasitological confirmatory tests remains insufficient and needs to be improved. Screening for T. b. rhodesiense infection still relies on clinical features in the absence of serological tests available for field use. Ongoing research is opening perspectives for a new generation of field diagnostics. Also essential for both forms of HAT is accurate determination of the disease stage because of the high toxicity of melarsoprol, the drug most widely used during the neurological stage of the illness. Recent studies have confirmed the high accuracy of raised immunoglobulin M levels in the cerebrospinal fluid for the staging of T. b. gambiense HAT, and a promising simple assay (LATEX/IgM) is being tested in the field. Apart from the urgent need for better tools for the field diagnosis of this neglected disease, improved access to diagnosis and treatment for the population at risk remains the greatest challenge for the coming years.

IgM quantification in the cerebrospinal fluid of sleeping sickness patients by a latex card agglutination test

An increased IgM concentration in cerebrospinal fluid (CSF), occurring as a consequence of massive intrathecal IgM synthesis, is a marker of interest for diagnosis of the meningo-encephalitic stage in human African trypanosomiasis. However, in current practice, IgM in CSF is not determined because of the lack of a simple and robust test that is applicable in African rural regions where the disease prevails. We describe the development of a sensitive semiquantitative card agglutination test, LATEX/IgM, for IgM quantification in CSF. The test is simple and fast and the lyophilized reagent remains stable even at 45 degrees C. CSF end-titres obtained with LATEX/IgM parallel the IgM concentrations determined by nephelometry and enzyme-linked immunosorbent assay. Detection of intrathecal IgM synthesis is the most sensitive marker for CNS involvement in sleeping sickness. At a cut-off value of >or= 8, the sensitivity and specificity of LATEX/IgM for intrathecal IgM synthesis are 89.4 and 92.7%. As a consequence, patients with LATEX/IgM end-titres >or= 8 are likely to have intrathecal IgM synthesis, thus central nervous system involvement and therefore should be treated accordingly. Further studies should concentrate on the relationship between the LATEX/IgM end-titres, presence of intrathecal IgM synthesis and occurrence of treatment failures in patients treated with pentamidine.

Preliminary studies by ELISA on the antigen and antibody dynamics in the early stages of experimental infections with Trypanosoma evansi in cattle

Six 6-month-old bulls were experimentally infected with five different isolates of Trypanosoma evansi; two received the same isolate and the other four received different isolates. The parasitaemias and serum antigen levels were monitored regularly by the haematocrit centrifuge technique (HCT) and antigen-detection ELISA (Ag-ELISA), respectively. Trypanosomal antigen was demonstrated by the Ag-ELISA by 10-14 days post inoculation in four cattle, while parasitaemias were first found to be positive in individual cattle over a longer period of time post inoculation (6-28 days). In two cattle, the Ag-ELISA values were also positive when the animals were found to harbour trypanosomes by the HCT and only turned negative 3 days after treatment, while the ELISA values fluctuated during the experiment in another two bulls. The remaining two cattle never produced positive ELISA results despite positive parasitological results. The antibody titres in all six cattle started to rise around 10 days post inoculation and then stayed high throughout the experiment. It was concluded that the Ag-ELISA would produce some false negative results in the early stages of T. evansi infection owing to variations in the balance of parasitaemia and antibody levels in the circulation, and in the pathogenicity of parasite strains.

A preliminary comparative study of a dipstick colloidal dye immunoassay and two antigen-detection ELISAs for diagnosis of Trypanosoma evansi infection in cattle

A dipstick colloidal dye immunoassay (DIA) was developed for the field diagnosis of Trypanosoma evansi infection using affinity-purified polyclonal antibodies (PcAbs) and the monoclonal antibody (McAb) 8B9. PcAbs were adsorbed onto Palanil Red dye particles and used as dye reagents. Dipsticks were dotted with four different antibodies; normal rabbit and mouse IgGs as negative controls, and anti-T. evansi PcAb and McAb 8B9, which capture trypanosome antigens in the tested samples. Since the dye reagent bound to the captured antigens, the presence of coloured dots on the dipstick identified trypanosome infections. The sensitivity of the DIA was compared with two antigen detection ELISAs (Ag-ELISA); one was PcAb-based and the other was based on a combination of the same Mc- and PcAbs as were employed for the DIA. With a positive serum, the DIA detected trypanosomal antigen up to a dilution of 1:500 for both the PcAb and McAb dots, at which dilution the PcAb- and combination-based Ag-ELISA gave positive OD readings of 0.13 and 0.36, respectively. When 124 field sera were tested, circulating antigens were detected in 51 (41%) samples by the DIA, and 76 (61%) and 49 (40%) samples by the PcAb- and combination-based Ag-ELISAs respectively, of which 48 (63%) and 34 (69%) were also positive by the DIA.

Effect of anti-immunoglobulin antibodies produced in cattle infected with Trypanosoma evansi on antigen detection ELISA

The possibility of interference with the antigen-detection ELISA for trypanosomosis by anti-rodent IgG antibodies produced in cattle infected with Trypanosoma evansi was investigated. Two different ELISA for detection of trypanosome antigen and three different systems for anti-rodent IgG antibody detection were established. The former two were respectively polyclonal antibody-based and a combination of monoclonal and polyclonal antibody-based assays. The latter three were also adapted for detection of anti-mouse IgG, anti-rabbit IgG and anti-IgG antibodies cross-reactive with both rabbit and mouse IgGs. A total of 170 samples were collected from a dairy cattle farm where an outbreak of T. evansi infection was reported. One hundred and two cattle (59%) were found to be positive for trypanosome antigens by the polyclonal antibody-based assay and 86 (51%) were positive by the combination-based system. On the other hand, 51 (30%) and 10 (6%) of cattle had anti-rabbit and anti-mouse IgG antibodies respectively but none had antibodies cross-reactive with both IgGs. Of the 102 cattle positive for trypanosome antigens in the polyclonal antibody-based ELISA, 48 (47%) were also anti-rabbit IgG antibody positive. It is concluded that antigen detection ELISA based on a single-species immunoglobulin for capture and detection might misdiagnose T. evansi infection. Results indicate that this bias will be avoided if reagents for capture and detection are derived from different species.

A semi-quantitative ELISA for detection of Trypanosoma brucei gambiense specific antibodies in serum and cerebrospinal fluid of sleeping sickness patients

A semi-quantitative ELISA, using variable surface glycoprotein of T.b. gambiense as antigen, was developed for the detection of antibodies of different immunoglobulin isotypes in serum and cerebrospinal fluid of sleeping sickness patients. Using the assay, the antibody profiles of paired serum and cerebrospinal fluid samples of 28 patients have been studied. Total concentrations of various Ig isotypes were determined as well. In serum and cerebrospinal fluid a drastic increase in IgG, basically IgG1, as well as in IgM levels was observed. The concentration of IgA remained relatively normal. The antitrypanosomal antibodies detected in serum and cerebrospinal fluid were mainly of the IgG (IgG1 and IgG3) and IgM isotypes. Measurement of immunoglobulin and trypanosome specific antibody concentrations in serum and CSF allows calculation of intrathecal antibody synthesis and is a possible tool for determining the clinical stage of sleeping sickness.

A multiple antigen detection dipstick colloidal dye immunoassay for the field diagnosis of trypanosome infections in cattle

Monoclonal antibodies (McAbs) were developed against aspartate aminotransferase purified from Trypanosoma brucei rhodesiense bloodstream form (bf) soluble extracts using a combination of anion-exchange and hydrophobic interaction chromatography. McAb 1A1 was Trypanozoon and Nannomonas specific while 2F1 was Trypanozoon bloodstream form specific. A dipstick colloidal dye immunoassay (DIA) was employed as a field diagnostic test for African trypanosome infections and designed using affinity purified polyclonal antibodies (PcAbs) raised against T. b. rhodesiense bf and the two McAbs, 1A1 and 2F1. PcAbs were adsorbed onto Palanil Red dye particles and used as dye reagents. Dipsticks were dotted with the three different antibodies, which captured trypanosomal antigens in samples tested, while the dye reagent bound to the captured antigens; the presence of coloured dots on the dipstick identified trypanosome infections. A field trial of the DIA was carried out in southeastern Uganda. A total of 1686 cattle from seven areas were bled and tested by DIA and haematocrit centrifuge technique (HCT). A total of 798 cattle (47.3%) were found to be trypanosomal antigen positive by DIA while only 162 (9.6%) were revealed to harbour trypanosomes by HCT, of which 151 (93%) were also positive by DIA.

The sheep (Ovis aries) as an experimental model for African trypanosomiasis. II. Biological study

Sheep that have been experimentally infected with a strain of Trypanosoma brucei brucei reproduce the clinical symptomatology of human African trypanosomiasis. We measured two biochemical parameters which are altered during the infection; total serum and cerebrospinal fluid (CSF) proteins, and the time of appearance and levels of IgM in both serum and CSF. Serum protein levels were considerably raised (up to 90 gl-1), although in CSF the levels were always less than 1 gl-1. The ratio of serum albumin to globulins fell to a value of 0.40 during the course of the disease. Electrophoresis of CSF proteins demonstrated the appearance of polyclonal immunoglobulins. Plasma IgM levels rose to ten times normal values, and after the sixth week IgMs made up 10% of total CSF protein content. Specific antibodies were detected, by both indirect immunofluorescence and an ELISA technique, within two weeks after infection in the blood and after four weeks in the CSF.

Difluoromethylornithine, an effective new treatment of Gambian trypanosomiasis. Results in five patients

Recent studies have shown DL-alpha-difluoromethylornithine (eflornithine), an inhibitor of polyamine biosynthesis, to be curative in various Trypanosoma species infections of laboratory animals. Five patients are described with Gambian trypanosomiasis treated in Belgium with difluoromethylornithine, using various intravenous and oral dosage schedules. Three patients had late-stage and two had early-stage disease. Difluoromethylornithine treatment was associated with clearing of parasites from blood within one to four days, a trend towards normalization of all altered biologic values associated with the disease, and marked amelioration of clinical symptoms. Side effects of difluoromethylornithine, including loose stools in three patients and both anemia, and a decrease in auditory acuity in one patient, were mild, transient, and never required interruption of drug treatment. The presence of difluoromethylornithine in cerebrospinal fluid, determined in three patients, demonstrated that difluoromethylornithine penetrates into the central nervous system. In three patients, follow-up of at least 24 months after treatment demonstrated a continued healthy state without evidence of relapse. These promising, albeit preliminary, results of difluoromethylornithine therapy, even in patients with central nervous system involvement, indicate that extended clinical trials are warranted to determine the optimal dosage regimen in patients with early- and late-stage disease.

Treatment of gambiense sleeping sickness in the Sudan with oral DFMO (DL-alpha-difluoromethylornithine), an inhibitor of ornithine decarboxylase; first field trial

Difluoromethylornithine (DFMO), a specific, irreversible inhibitor of polyamine biosynthesis shown to be curative in animal models inoculated with various Trypanosoma spp., was evaluated in the Southern Sudan in a preliminary open clinical field trial in patients infected with Trypanosoma brucei gambiense. 20 patients were studied including 18 with late-stage disease involving the central nervous system, 16 of whom were refractory to arsenical treatment. In late-stage disease monotherapy with oral DFMO doses of about 400 mg/kg/day for five to six weeks was associated with disappearance of parasites from cerebrospinal fluid (CSF), decreased CSF WBC counts and protein concentrations and reversal of clinical signs. Side effects associated with this dose regimen included diarrhoea, abdominal discomfort and anaemia, but were seldom sufficiently severe to prompt discontinuing therapy. In early-stage patients about 200 mg/kg/day for six weeks appears adequate to eliminate parasites and reverse clinical symptoms and is well tolerated. Three cases of late-stage sleeping sickness and two of early-stage disease followed up for approximately one and a half to two years after treatment indicated that DFMO monotherapy can be curative. Additional studies are needed to define optimal posology. Inhibition of polyamine biosynthesis is a promising new approach to therapy of trypanosomiasis.

The pathogenesis of sleeping sickness

Although the clinical and pathological features of sleeping sickness have been well recognized since the beginning of the century, we still have very little idea about how these changes are brought about. A convincing role for a trypanosome-derived toxin has yet to be established and it is probable that most tissue damage results from an immunopathological reaction. An immediate type hypersensitivity reaction might account for the pruritus and urticaria sometimes encountered in patients with the infection. Autoantibodies are produced by patients with sleeping sickness but it has not been established that these can cause tissue damage. Similarly, although high levels of immune complexes are found in patients with sleeping sickness, it has yet to be clearly established that these damage the brain or heart. The dominant pathological event in sleeping sickness is B lymphocyte proliferation, first within the lymph nodes and then within the brain and meninges, and this response may lead to tissue damage in some way which has not yet been identified. B lymphocyte proliferation could result from the action of a trypanosome-derived mitogen or from interference with T lymphocyte control over B lymphocyte function.

Enzyme immunoassay: a review

In the last few years, the use of enzyme labels in immunoassays has been investigated. The aim of this review is to evaluate critically the role of such labels in clinical biochemistry. Special attention has been given to the problems involved in preparing enzyme labels and the ways in which such labels can be used in a variety of heterogeneous and homogeneous assay systems.