Effect of chaotropes in Chagas disease and leishmaniasis cross-reacting serology assays for epidemiological surveys

Abstract INTRODUCTION: Serological cross-reactivity between leishmaniasis and Chagas disease, especially at low titers, leads to difficulties of the seroepidemiological interpretation. METHODS: We have studied the ability of urea as a chaotrope to select high-avidity antibodies in IgG ELISA, thus reducing low-avidity IgG cross-reactivity in serologically positive samples in both assays. RESULTS: Using 0.5M urea for diluting the sample efficiently defined leishmaniasis or double infections in high-avidity IgG ELISA and eliminated false-positive results. CONCLUSIONS: The use of a chaotropic diluting agent is useful for improving the specificity of Chagas disease and leishmaniasis immunoassays.

Diagnostic significance of immunoglobulin G avidity in symptomatic and asymptomatic West Nile virus infection

Abstract INTRODUCTION West Nile virus (WNV) immunoglobulin M (IgM) antibodies have been shown to persist for up to 500 days in certain patients. To evaluate the usefulness of immunoglobulin G (IgG) avidity assessment in the diagnosis of WNV infection, we analyzed 54 WNV IgM- and/or IgG-positive serum samples from 39 patients with neuroinvasive disease and 15 asymptomatic cases tested during a seroprevalence investigation. METHODS Serological tests (WNV IgM/IgG antibody detection, IgG avidity) were performed using commercially available enzyme-linked immunosorbent assays. RESULTS WNV IgM antibodies were detected in 47 (87%) samples. Acute/recent WNV infection was confirmed based on low/borderline avidity index (AI) in 44 IgM-positive samples (93.6%). In three IgM-positive samples (6.4%), high IgG AIs were detected, thus indicating persisting IgM antibodies from previous infections. All IgM-negative samples showed high AIs. Patients with WNV neuroinvasive disease tested within 30 days showed low AIs. In six patients tested 34-50 days after disease onset, AI was borderline (42%-60%), suggesting earlier WNV IgG maturation. Samples with the highest IgM values were associated with the lowest AIs (Spearman's rho coefficient -0.767, p < 0.001). CONCLUSIONS Our results indicate that IgG avidity differentiates current/recent WNV infection from persistent IgM seropositivity from the previous WNV transmission season both in patients with WNV neuroinvasive disease and in asymptomatic persons. A strong negative correlation between IgM antibody levels and AI indicates that in cases with very high IgM levels, determination of IgG avidity may not be necessary. As many patients showed rapid avidity maturation, low IgG avidity is indicative of WNV infection within the previous month.

Evaluación de un test comercial de avidez de IgG: Aporte al diagnóstico de primoinfección por Toxoplasma gondii / Evaluation of an IgG avidity commercial test: Contribution to diagnosis of primary infection caused by Toxoplasma gondii

Introduction: Toxoplasmosis (T) is a major chronic parasitic infection in immunocompromised patients and pregnant women. It is important to discriminate between acute phase (AT) and chronic phase (CT). Diagnosis is serological in immunocompetent patients (concentration of IgG and IgM). Objective: To evaluate the utility of an IgG avidity test (A-IgG) to identify the acute and chronic stage. Avidity is the strength of affinity between a specific immunoglobulin and the protein antigenic epitope of the infecting agent, an affinity that increases over time. Patients and Methods: We used a qualitative kit that measures the avidity of IgG, discriminating the two phases. In 35 patients with clinical diagnosis of AT and/or CT, IgG, IgM and IgG A (VIDAS®) were performed. Results: Patients with AT were positive for IgM and IgG, but presented weak avidity. In the 21 cases with CT, 52 percent (n: 11) were IgM positive and 100 percent (n: 21) had positive IgG with strong avidity. Discussion: The results confirm that the test of A-IgG may be useful in the diagnosis of AT, and has 100 percent concordance with reference test (qualitative IgM + quantitative IgG). The result is available within 24 hrs, and may be useful in diagnosis of AT in pregnant women.

Introducción: Toxoplasmosis (T) es una infección parasitaria crónica importante en pacientes inmunocompro-metidos y mujeres embarazadas. Es relevante discriminar entre fase aguda (TA) y fase crónica (TC). Su diagnóstico es serológico en inmunocompetentes (detección de IgG e IgM). Objetivo: Evaluar la utilidad del test de avidez IgG (A-IgG) para identificar la fase aguda y o crónica. Avidez es la fuerza de afinidad entre una inmunoglobulina específica y el epítope de la proteína antigénica del agente infectante, afinidad que aumenta con el tiempo. Pacientes y Métodos: Se usó un test cualitativo que mide la avidez de IgG, discriminando las dos fases. A 35 pacientes con diagnóstico clínico de TA y o TC, se les realizó IgG, IgM e A-IgG en Equipo VIDAS®. Resultados: Los pacientes con TA fueron positivos para IgM e IgG y presentaron avidez débil. Los 21 casos con TC 52 por ciento (n: 11) tuvieron IgM positivo y 100 por ciento (n: 21) tuvo IgG positiva con avidez fuerte. Discusión: Los resultados confirman que el test de A-IgG puede ser de gran utilidad en el diagnóstico de TA, concordancia: 100 por ciento con test de referencia (IgM cualitativa + IgG cuantitativa). El resultado está disponible en menos de 24 hrs, pudiendo ser útil en el diagnóstico de TA en mujeres embarazadas.

Congenital toxoplasmosis transmitted by human immunodeficiency-virus infected women

We report the occurrence of congenital toxoplasmosis in three infants born to HIV infected women who had high anti-toxoplasma IgG and negative IgM during pregnancy. We briefly reviewed available literature and discussed the possible transmission mechanisms of congenital toxoplasmosis among HIV infected pregnant women. Serum samples were tested for Toxoplasma gondii IgM and IgG antibodies using commercial enzyme immunoassay and IgG-avidity tests. In the first case, fetal death occurred at 28th week of gestation. In the second case, congenital toxoplasmosis was diagnosis at 6th month of life; and in the third case, an HIV-infected newborn, congenital toxoplasmosis was asymptomatic. These cases point out to the possibility of enhanced maternal-fetal transmission of T. gondii infection by HIV-infected women chronically infected, which may have important public health consequences, considering that increasing frequency of HIV-infection has been observed among women of childbearing age around the world.

Pattern of functional antibody activity against Haemophilus influenzae type b (Hib) in infants immunized with diphtheria-tetanus-pertussis/Hib Brazilian combination vaccine

We evaluated the functional activity of Haemophilus influenzae B (Hib) antibodies elicited in a group of infants immunized with the diphtheria-tetanus-pertussis vaccine combined with an Hib vaccine produced totally in Brazil after technological transfer of Hib vaccine production from Glaxo SmithKline, Belgium. Blood samples from immunized infants (N = 985) were collected for the determination of Hib antibodies. Total Ig and IgM and IgG subclasses of antibodies against polyribosyl ribitol phosphate (PRP) were analyzed by ELISA. Almost all vaccinees (97.56 percent, 961/985) developed a strong anti-PRP IgG antibody response (¡Ý1.0 ¦Ìg/mL), while an anti-PRP IgM response was observed in 64.24 percent (634/985) of them (¡Ý0.15 ¦Ìg/mL). Only 18.88 percent (186/985) of the infants in the group with high PRP antibody IgG concentrations (¡Ý1.0 ¦Ìg/mL) developed a high IgM antibody response. Anti-PRP IgG antibody levels were significantly higher than anti-PRP IgM. These results demonstrate the predominance of IgG antibodies over IgM antibodies in response to PRP, with a ratio of 17:1. IgG antibodies were predominantly of the IgG1 subclass. An increase in IgG avidity was also observed during the course of immunization.

Distinguishing between primary infection and reinfection with rubella vaccine virus by IgG avidity assay in pregnant women

During the mass measles/rubella vaccination campaign in 2003 in Iran, many pregnant women were vaccinated mistakenly or became pregnant within 1 month of vaccination. To distinguish pregnant women who were affected by rubella vaccine as primary infection from those who had rubella reinfection from the vaccine, serum samples were collected 1-3 months after the campaign from 812 pregnant women. IgG avidity assay showed that 0.3% of the women had no rubella-specific IgG response; 14.4% had low-avidity anti-rubella IgG and were therefore not immune to rubella before vaccination; 85.3% had high-avidity antirubella IgG and were regarded as cases of reinfection

Association of the presence of residual anti-Toxoplasma gondii IgM in pregnant women and their respective family groups in Miracema, Northwest Rio de Janeiro, Brazil

The seroprevalence of toxoplasmosis in 832 pregnant women in Miracema, Rio de Janeiro, was determined and 75.1 percent (625) and 2.0 percent (17) were anti-Toxoplasma gondii IgG and IgM positive, respectively. Out of the 17 IgM positive pregnant women, only one had low avidity IgG corresponding to the acute phase of the infection. All the other women presented with high avidity IgG and also presented with residual IgM anti-T. gondii. Of this sample, 106 received home visits (this includes 11 family nuclei of pregnant women with residual IgM anti-T. gondii, 68 nuclei of only IgG positive pregnant women and 27 nuclei of pregnant women with no antibodies to anti-T. gondii), resulting in 267 individuals visited. Out of these 267 individuals, 21 were positive for IgG and IgM anti-T. gondii and were candidates for the IgG avidity test. All of them presented with high avidity IgG and residual IgM. Five of these IgM+ individuals were (5/238; 2.1 percent) relatives of IgM negative pregnant women. The other 16 (16/29; 55.2 percent) were relatives of IgM+ pregnant women who were positive for residual IgM anti-T. gondii. This association was statistically significant (p = 0.0000). The analysis presented herein raises questions regarding the presence of residual IgM anti-T. gondii such as genetic determinants or even constant antigenic stimuli for the same family cluster.

Correlation between specific IgM levels and percentage IgG-class antibody avidity to Toxoplasma gondii / Correlação entre níveis de IgM específica e percentual de avidez de anticorpos da classe IgG ao Toxoplasma gondii

Toxoplasmosis is an usually asymptomatic worldwide disseminated infection. In its congenital presentation it may lead to abortion or fetal malformations. Antenatal evaluation is considered of paramount importance to identify seronegative women and allow for prophylaxis. Recent improvements in sensitivity of IgM tests has made IgM detection an extremely protracted acute phase marker, and IgG avidity evaluation test became necessary. Observation has shown that a correlation can be established between IgM levels and avidity percentages, suggesting that frequently the avidity test may not be necessary. In this study we analyzed Toxoplasma gondii IgM levels of 202 samples and their IgG avidity percentages, in order to define specific levels whose IgM quantification could by itself define serodiagnosis and therefore make the avidity evaluation unnecessary. We showed that for IgM levels bellow 2.0 and above 6.0 serodiagnosis of toxoplasmosis could be established without need of IgG avidity test. IgM levels between these two parameters are associated with varying avidity indexes highlighting the importance of its evaluation as a means to confirm toxoplasmosis. Following this demonstration it was possible to avoid the avidity test for 75 percent of the cases, to reduce the turnaround time and to reduce costs.

A Toxoplasmose é uma infecção universal e usualmente assintomática. A forma congênita, entretanto, pode resultar em aborto ou mal formações. Testes sorológicos estão indicados em situações onde há suspeita clínica, e na triagem pré-natal, quando são extremamente importantes para rastrear a infecção e orientar a gestante. O aumento da sensibilidade das técnicas para detecção de IgM, tornou necessário o desenvolvimento de recursos, como a avidez de IgG, visando obter novo marcador de infecção aguda. Embora exista correlação entre níveis de IgM e grau de avidez de IgG, a maioria dos testes de avidez associa-se a níveis baixos de IgM, sugerindo que o teste de avidez não fosse necessário. Portanto, correlacionamos níveis de IgM de 202 amostras com seu respectivo nível de avidez de IgG, dirigidos contra o Toxoplasma, objetivando estabelecer valores claros para a sua indicação. Pôde-se observar que, para IgM < 2,0 e > 6,0, a definição sorológica pode ser feita independentemente da avidez. Níveis de IgM dentro desse intervalo associam-se a índices variados de avidez e, portanto, ressaltam a importância deste teste para definição sorológica do quadro. Com essa abordagem, foi possível diminuir a indicação do teste de avidez em 75 por cento, reduzir o tempo para liberação dos resultados e o custo unitário do teste para IgM.

Avidity of IgG antibodies against excreted/secreted antigens of Toxoplasma gondii: immunological marker for acute recent toxoplasmosis / Avidez de anticorpos IgG anti-antígeno de secreção e excreção de Toxoplasma gondii: marcador imunológico de toxoplasmose aguda recente

Detection of anti-toxoplasma IgM antibodies has frequently been used as a serological marker for diagnosing recently acquired toxoplasmosis. However, the persistence of these antibodies in some patients has complicated the interpretation of serological results when toxoplasmosis is suspected. The purpose of the present study was to evaluate the avidity of IgG antibodies against excreted/secreted antigens of Toxoplasma gondii by means of immunoblot, to establish a profile for acute recent infection in a single serum sample and confirm the presence of residual IgM antibodies obtained in automated assays. When we evaluated the avidity of IgG antibodies against excreted/secreted antigens of Toxoplasma gondii by means of immunoblot, we observed phase-specific reactivity, i.e. cases of acute recent toxoplasmosis presented low avidity and cases of non-acute recent toxoplasmosis presented high avidity towards the 30kDa protein fraction, which probably corresponds to the SAG-1 surface antigen. Our results suggest that the avidity of IgG antibodies against excreted/secreted antigens of Toxoplasma gondii is an important immunological marker for distinguishing between recent infections and for determining the presence of residual IgM antibodies obtained from automated assays.

A detecção de anticorpos IgM antitoxoplasma tem sido freqüentemente utilizada como marcador sorológico para o diagnóstico de toxoplasmose de aquisição recente. Entretanto, a persistência destes anticorpos em alguns pacientes tem complicado a interpretação dos resultados sorológicos quando a toxoplasmose é suspeitada. A proposta deste trabalho foi avaliar a avidez de anticorpos IgG contra antígenos de secreção e excreção de Toxoplasma gondii por immunoblot, para estabelecer um perfil de infecção recente aguda em uma única amostra de soro e confirmar a presença de anticorpos IgM residuais obtidos nos testes automatizados. Quando a avidez de anticorpos IgG contra antígenos de secreção e excreção Toxoplasma gondii, por immunoblot, foi avaliada, observou-se reatividade estágio específica, ou seja, casos de toxoplasmose aguda recente apresentaram baixa avidez e os casos de infecção recente não aguda apresentaram alta avidez para a fração protéica de 30kDa, que corresponde provavelmente ao antígeno de superfície- SAG-1. Nossos resultados sugerem que a avidez dos anticorpos IgG contra antígenos de secreção e excreção Toxoplasma gondii é um importante marcador imunológico para distinguir doença recente de infecção e determinar a presença de anticorpos IgM residuais detectados nos testes automatizados.

Characterization of a novel anti-human TNF-alpha murine monoclonal antibody with high binding affinity and neutralizing activity

In order to develop an anti-human TNF-alpha mAb, mice were immunized with recombinant human TNF-alpha. A murine mAb, TSK114, which showed the highest binding activity for human TNF-alpha was selected and characterized. TSK114 specifically bound to human TNF-alpha without cross-reactivity with the homologous murine TNF-alpha and human TNF-beta TSK114 was found to be of IgG1 isotype with kappa light chain. The nucleotide sequences of the variable regions of TSK114 heavy and light chains were determined and analyzed for the usage of gene families for the variable (V), diversity (D), and joining (J) segments. Kinetic analysis of TSK114 binding to human TNF-alpha by surface plasmon resonance technique revealed a binding affinity (KD) of ~5.3 pM, which is about 1,000- and 100-fold higher than those of clinically relevant infliximab (Remicade) and adalimumab (Humira) mAbs, respectively. TSK114 neutralized human TNF-alpha-mediated cytotoxicity in proportion to the concentration, exhibiting about 4-fold greater efficiency than those of infliximab and adalimumab in WEHI 164 cells used as an in vitro model system. These results suggest that TSK114 has the potential to be developed into a therapeutic TNF-alpha-neutralizing antibody with picomolar affinity.

Anti-VP1 and anti-VP2 antibodies detected by immunofluorescence assays in patients with acute human parvovirus B19 infection

Acute human parvovirus B19 infection is followed by an antibody response to the structural proteins of the viral capsid (VP1 and VP2). We used 80 sera collected from 58 erythema infectiosum and 6 transient aplastic crisis patients to test IgM and IgG antibodies against these two proteins in an immunofluorescence assay (IFA) using Sf9 cells infected with recombinant baculovirus expressing either VP1 or VP2 antigen. Although less sensitive than IgM capture enzyme immunoassay using native antigen (MACEIA), we could detect anti-VP1 or anti-VP2 IgM antibodies by IFA in 49 patients with acute infection (76.6 percent). Detection of IgG anti-VP1 and anti-VP2 by IFA, however, was as sensitive as IgG detection by indirect enzyme immunoassay. By applying IgG avidity IFA to sera of the 15 IgM IFA negative patients we were able to confirm acute infection in further 12 cases by IFA. Overall, acute infection was confirmed by IFA in 61 (95.3 percent) of the 64 patients

IgG recognizing 21-24 kDa and 30-33 kDa tachyzoite antigens show maximum avidity maturation during natural and accidental human toxoplasmosis

We describe the avidity maturation of IgGs in human toxoplasmosis using sequential serum samples from accidental and natural infections. In accidental cases, avidity increased continuously throughout infection while naturally infected patients showed a different profile. Twenty-five percent of sera from chronic patients having specific IgM positive results could be appropriately classified using exclusively the avidity test data. To take advantage of the potentiality of this technique, antigens recognized by IgG showing steeper avidity maturation were identified using immunoblot with KSCN elution. Two clusters of antigens, in the ranges of 21-24 kDa and 30-33 kDa, were identified as the ones that fulfill the aforementioned avidity characteristics

Serological diagnosis of toxoplasmosis: usefulness of IgA detection and IgG avidity determination in a patient with a persistent IgM antibody response to Toxoplasma gondii

No presente trabalho, sao descritos os resultados da deteccao de anticorpos especificos da classe IgA e da determinacao da avidez dos anticorpos IgG em amostras sequenciais de soro de um paciente apresentando niveis significativos de anticorpos IgM anti-Toxoplasma gondii durante sete anos apos o inicio das manifestacoes clinicas da infeccao. Os anticorpos...

Avaliação da avidez dos anticorpos séricos IgA, IgM, IgG e subclasses de IgG reativos ao antígeno solúvel de ovo do Schistosoma mansoni em indivíduos com as fases aguda e crônica da esquistossomose mansoni / Evaluation of the avidity of serum antibody IgA, IgM, and IgG subclasses of IgG reactive to the soluble egg antigen of Schistosoma mansoni in individuals with acute and chronic phases of schistosomiasis mansoni

A avidez dos anticorpos refere-se à força da interação antígeno-anticorpo. Durante a resposta imune a diversas infecções, observa-se aumento progressivo da avidez dos anticorpos. Foram determinados os níveis séricos dos anticorpos IgA, IgM, IgG e subclasses de IgG reativos ao antígeno solúvel de ovo do Schistosoma mansoni (SEA) em 36 indivíduos com a fase aguda da esquistossomose mansoni e 40 indivíduos com esquistossomose mansoni crônica. Quinze indivíduos com a fase aguda foram avaliados ao diagnóstico clínico e novamente seis meses após. Calculou-se o índice de avidez dividindo-se a absorbância detectada ao Elisa convencional por aquela detectada ao Elisa empregando-se dietilamina (agente eluidor). Os níveis dos anticorpos IgG, IgG2 e IgG3 foram superiores nos indivíduos com a fase aguda (p = 0,000). Esta diferença não foi observada em relação aos anticorpos IgG1 anti-SEA. Para as imunoglobulinas citadas, os índices de avidez em indivíduos com a fase aguda da esquistossomose foram estatisticamente inferiores (p = 0,000). Anticorpos IgG4 anti-SEA foram detectados em apenas dois indivíduos com a fase aguda da esquistossomose, sendo 0,06 e 0,81 os respectivos índices de avidez. Em indivíduos com esquistossomose crônica, a média do índice de avidez para IgG4 foi de 0,84. Os níveis dos anticorpos IgM foram mais elevados em indivíduos com a fase aguda da esquistossomose (p = 0,000) e os índices de avidez foram similares entre os dois grupos (índice de avidez médio: 0,31). Na fase aguda, foram detectados altos níveis de anticorpos IgA anti-SEA e, em indivíduos com esquistossomose crônica, estes níveis se aproximaram de zero. Os índices de avidez mostraram-se inferiores na fase aguda (p = 0,000). Aos seis meses de acompanhamento dos indivíduos com a fase aguda da esquistossomose, observou-se aumento da avidez em relação aos anticorpos IgG1 e IgG3 (p = 0,000), sem alterações em relação às demais imunoglobulinas.

Avaliação da avidez dos anticorpos séricos IgA, IgM, IgG e subclasses de IgG reativos ao antígeno solúvel de ovo do Schistosoma mansoni em indivíduos com as fases aguda e crônica da esquistossomose mansoni

A avidez dos anticorpos refere-se à força da interação antígeno-anticorpo. Durante a resposta imune a diversas infecções, observa-se aumento progressivo da avidez dos anticorpos. Foram determinados os níveis séricos dos anticorpos IgA, IgM, IgG e subclasses de IgG reativos ao antígeno solúvel de ovo do Schistosoma mansoni (SEA) em 36 indivíduos com a fase aguda da esquistossomose mansoni e 40 indivíduos com esquistossomose mansoni crônica. Quinze indivíduos com a fase aguda foram avaliados ao diagnóstico clínico e novamente seis meses após. Calculou-se o índice de avidez dividindo-se a absorbância detectada ao Elisa convencional por aquela detectada ao Elisa empregando-se dietilamina (agente eluidor). Os níveis dos anticorpos IgG, IgG2 e IgG3 foram superiores nos indivíduos com a fase aguda (p = 0,000). Esta diferença não foi observada em relação aos anticorpos IgG1 anti-SEA. Para as imunoglobulinas citadas, os índices de avidez em indivíduos com a fase aguda da esquistossomose foram estatisticamente inferiores (p = 0,000).

Anticorpos IgG4 anti-SEA foram detectados em apenas dois indivíduos com a fase aguda da esquistossomose, sendo 0,06 e 0,81 os respectivos índices de avidez. Em indivíduos com esquistossomose crônica, a média do índice de avidez para IgG4 foi de 0,84. Os níveis dos anticorpos IgM foram mais elevados em indivíduos com a fase aguda da esquistossomose (p = 0,000) e os índices de avidez foram similares entre os dois grupos (índice de avidez médio: 0,31). Na fase aguda, foram detectados altos níveis de anticorpos IgA anti-SEA e, em indivíduos com esquistossomose crônica, estes níveis se aproximaram de zero. Os índices de avidez mostraram-se inferiores na fase aguda (p = 0,000). Aos seis meses de acompanhamento dos indivíduos com a fase aguda da esquistossomose, observou-se aumento da avidez em relação aos anticorpos IgG1 e IgG3 (p = 0,000), sem alterações em relação às demais imunoglobulinas.

Incomplete dominance of the low antibody response to Cryptosporidium parvum antigens in mice selected for high and low antibody responsiveness

The humoral antibody response to Cryptosporidium was investigated in mice genetically selected for high (H) and low (L) antibody responsiveness. Groups of 4-5 mice from two different selections, general primary (GP) and general secondary (GS), were studied. Following immunization with Cryptosporidium parvum antigens, the maximum levels of IgG in the HGP, (X ñ SD = 1.13 ñ 0.35, N = 5) and in the HGS (0.42 ñ 0.15, N = 4) lines, and of IgM in the HGP line (0.86 ñ 0.53, N = 5) were significantly higher than those in their L counterparts (0.04 ñ 0.02, N = 5;0.05 ñ 0.02, N = 4 and 0.24 ñ 0.07, N = 5, respectively). These findings were similar to those reported for other immunogens. However, the IgG (0.22 ñ 0.05, N = 4) and the IgM (0.33 ñ 0.08, N = 4) responses to immunization of F1 (LGP x HGP) hybrids indicated an incomplete dominance of the low response, in contrast to the incomplete dominance of the high response described for many other antigens and representing an important exception. In addition, the H, L and F1 mice did not develop detectable infections when inoculated with live Cryptosporidium oocysts, supporting the view that a reduced or zero antibody production itself is not enough to permit the establishment of Cryptosporidium infection in adult mice.

Effect of fixed epimastigote forms of Trypanosoma cruzi on the hemocytes and the prophenoloxidase-activating system of the crayfish Pacifastacus leniusculus

The effect of the parasite Trypanosoma cruzi on the hemocystes and the prophenoloxidase (proPO)-activating system of the crayfish Pacifastacus leniusculus was studied. Incubation of the crayfish hemocyte lysate with fixed epimastigote forms of the parasites (4 x 10(5) cells/ml) induced a marked activation of the crayfish proPO system, measured as phenoloxidase activity. The activation of proPO by the parasite was much stronger (7-fold) than that induced by beta-1,3-glucans (1 mg/ml) which are known to be efficient elicitors of the proPO system. The fixed parasites promoted the spreading and degranulation of different populations of the crayfish hemocytes isolated by Percoll gradients, and were often observed to be attached to the crayfish hemocytes in rosette-like fashion. The attachment of the epimastigote forms of T. cruzi to the crayfish blood cell surface was not dependent on the adhesive 76-kDa protein released by the crayfish hemocytes, since the exocytotic inhibitor SITS and monospecific antibodies to the 76-kDa protein did not prevent parasite adhesion. The crayfish hemocytes apparently are able to phagocytose the fixed epimastigote forms of T. cruzi in vitro.

Relación entre el tiempo de evolución de la brucelosis humana y la avidez de anticuerpos IgG específicos / Relationship between evolution time of human brucellosis and the avidity of specific IgG antibodies

The aim of this work was to relate the avidity of specific IgG antibodies with the time of evolution of human brucella infection. IgG anti-brucella antibodies were measured using an ELISA assay with 8 M urea in 17 patients with recent active brucellosis (group I), 31 patients with chronic active brucellosis (group II) and 120 asymptomatic patients with past brucellosis (group III). Twelve patients of group I (70.6 percent), three of group II (9.7 percent) and none in group III had low avidity antibodies against Brucella. It is concluded that these antibodies have a high diagnostic efficiency for recent Brucella infections

Avidez de anticorpos IgG especificos como marcadores de infeccao primaria recente pelo Toxoplasma gondii / Avidity of especific IgG antibodies as markers of recent primary infection caused by Toxoplasma gondii

A caracterizacao de infeccao primaria recente pelo Toxoplasma gondii se apoia principalmente na presenca, no soro, de anticorpos especificos IgM. Para fins diagnosticos de toxoplasmose aguda, ou de contagio recente, a possibilidade de outros marcadores e altamente desejavel. Um marcador de infeccao recente atualmente referido e a baixa afinidade ou avidez de anticorpos especificos IgG. Para avaliacao do novo marcador, titularam-se os soros contra poliantigenos do T.gondii pelo teste imunoenzimatico (ELISA), antes e apos tratamento dos complexos antigeno-anticorpo formados, com solucao de ureia 6 M como agente dissociante. O deslocamento de anticorpos de baixa avidez foi indicado por uma queda de titulos, calculada em porcentagem em relacao aos titulos iniciais. Foram estudados 69 soros, 23 de cada um dos 3 perfis sorologicos sucessivos, observados na infeccao, e que a caracterizam respectivamente como recente, em fase de transicao e cronica. Os perfis foram determinados segundo os resultados de uma bateria de testes, incluindo os de imunofluorescencia IgG e IgM, de captura de anticorpos IgM e de hemaglutinacao. Para os soros de infeccao cronica a queda observada foi de 3 por cento ñ 3 por cento, de 34 por cento ñ 12 por cento para toxoplasmose recente e de 12 por cento ñ 9 por cento para a fase de transicao...