Modulation of parasitemia and antibody responce to Trypanosoma cruzy by cyclophosphamide in Calomys callosus (Rodentia, Cricetidae)

Calomys callosus a wild rodent, previously described as harboring Trypanosoma cruzi, has a low susceptibility to infection by this protozoan. Experiments were designed to evaluate the contribution of the immune response to the resistance to T. cruzi infection exhibited by C. calossus. Animals were submitted to injections of high (200 mg/kg body weight) and low (20 mg/kg body weight) doses of cyclophosphamide on days -1 or -1 and +5, and inoculated with 4 x 10³ T. cruzi on day O. Parasitemia, mortality and antibody response as measured by direct agglutination of trypomastigotes were observed. Two hundred mg doses of cyclophosphamide resulted in higher parasitemia and mortality as well as in suppression of the antibody response. A single dose of 20 mg enhanced antibody levels on the 20th day after infection, while an additional dose did not further increase antibody production. Parasitemia levels were not depressed, but rather increased in both these groups as compared to untreated controls. Passive transfer of hyperimmune C. callosus anti-T. cruzi serum to cyclophosphamide immunosuppressed animals resulted in lower parasitemia and mortality rates. These results indicate that the immune response plays an important role in the resistance of C. callossus to T. cruzi.

Prevalence of HTLV-I antibody among two distinct ethnic groups inhabiting the Amazon region of Brazil

HTLV-I seroprevalences of 3.63% (02/55), 12.19% (10/82) and 13.88% (10/72) were demonstrated among Tiryio, Mekranoiti and Xicrin Amazonian Indians, respectively, by the Western blotting enzyme assay (WBEI). By indirect immuno electron microscopy (IIEM), 2 Tiriyo, 9 Mekranoiti and 6 Xicrin Amerindians were reactive. Of 44 serum samples from Japanese immigrants, none reacted by any of the techniques before mentioned. One, 8 and 6 serum samples from Tiryio, Mekranoiti and Xicrin Indians, respectively, were both WBEI and IIEM positive. Our results strongly suggest that HTLV-I and/or an HTLV-I antigenic variant circulate (s) among populations living in the Amazon region of Brazil.

Immunization aganist hepatitis B in children from endemic zone: evaluation of the antibody response against the DNA recombinant vaccine (Engerix B-20 mcg)

A previous seroepidemiological study in the rural zone of Vargem Alta (ES) SouthEast of Brazil, showed a prevalence of up to 9% of hepatitis B surface antigen (HBsAg) in some areas. One hundred susceptible children aging 1 to 5 years old were selected and immunized with a recombinant DNA hepatitis B vaccine (Smith-Kline 20 mcg) using the 0-1-6 months vaccination schedule. Blood samples were collected at the time of the first vaccine dose (month 0) in order to confirm susceptible individuals and 1,3,6 and 8 months after the first dose , to evaluate the antibody response. Our results showed that two and five months after the second dose, 79% and 88% of children seroconverted respectively, reaching 97% after the third dose. The levels of anti-HBs were calculated in milli International Units/ml (mIU/ml) and demonstrated the markedly increase of protective levels of antibodies after the third dose. These data showed a good immunogenicity of the DNA recombinant hepatitis B vaccine when administered in children of endemic areas.

Reduced schedule of human anti-rabies immunization with Fuenzalida & Palacios vaccine: additional data

It was reevaluated a reduced schedule for anti-rabies post-exposure immunization with newborn mice nervous tissue vaccine (Fuenzalida 8c Palacios) in a group of 30 non exposed volunteers. The vaccine was administered by intramuscular injections on days zero, 2, 4, 16 and 27, in the deltoid area. Antibody levels were determinated by a simplified serum neutralization microtest on days zero, 16 and 37. On days 16 and 37 the antibody levels of the whole group was >0.5 IU/ml and >1.0 IU/ml, respectively. The cell mediated immunity was precociously detected (on day 4) by the delayed type hipersensitivity skin test. Our results show that this reduced schedule elicited an early and effective humoral and cellular immune response. However it is necessary other studies with larger groups of vaccinees in order to obtain definitive conclusion.

Schistosoma mansoni: identification of a 46KDa antigen of the schistosomular surface by monoclonal antibody

An IgG2a subclass monoclonal antibody, C6G9, was obtained by immunization of BALB/c mice with Schistosoma mansoni egg antigens. With this monoclonal antibody, it was possible to identify a schistosomular antigen with a molecular weight of 46 kilodaltons (KDa), and its expression being evaluated by means of indirect immunofluorescence. The antigen persisted in the integument of the developing schistosomulum, for at least 96 hours post-transformation. The monoclonal antibody also reacted with the cercaria surface, but not with that of adult worm. The C6G9 was also able to mediate significant levels of cytotoxicity in the presence of complement for newly transformed schistosomula.

Entamoeba histolytica: detection of coproantigens by purified antibody in the capture sandwich ELISA

A sensitive and specific Capture Sandwich ELISA (CSE) was developed using polyclonal purified rabbit antibodies against three different axenic strains of Entamoeba histolytica: CSP from Brazil and HM1 - IMSS from Mexico, for the detection of coproantigens in fecal samples. Immunoglobulin G (IgG) againstis E. histolytica was isolated from rabbits immunized with throphozoites whole extract in two stages: affinity chromatography in a column containing E. histolytica antigens bound to Sepharose 4B was followed by another chromatography in Sepharose antibodies 4B-Protein A. A Capture Sandwich ELISA using purified antibodies was able to detect 70ng of amebae protein, showing a sensitivity of 93% and specificity of 94%. The combination of microscopic examination and CSE gave a concordance and discordance of 93.25% and 6.75%, respectively. It was concluded that CSE is highly specific for the detection of coproantigens of E. histolytica in feces of infected patients, is quicker to perform, easier and more sensitive than microscopic examination.

Monoclonal antibody to serotype 17 of Neisseria meningitidis and their prevalence in Brazilian States

Neisseria meningitidis are gram-negative diplococci responsible for cases of meningococcal disease all over the world. The epidemic potential of N. meningitidis serogroup B and C is clearly a function of their serotype antigens more than of their capsular polysaccharides. Until recently, hiperimmune sera were used to detect typing antigens on the bacteria. The advent of monoclonal antibodies (MAbs) offered the opportunity to eliminate many of the cross-reactions and have improved the accuracy and reproducibility of meningococcal serotyping. We have produced a MAb to the outer membrane protein of the already existent serotype 17 that have been detected by the use of hiperimmune rabbit sera. The prevalence of this serotype epitope is low in the Brazilian strains. By using the MAb 17 we could not decrease the percentage of nontypeable serogroup C strains. However, there were a decreasing in nontypeable strains to 13% into serogroup B strains and to 25% into the other serogroups.

Natural killer cell activity in experimental paracoccidioidomycosis of the Syrian hamster

The study evaluated the activity of NK cells during the course of experimental infection of hamsters with Paracoccidioides brasiliensis. Eigthy hamsters were infected with P. brasiliensis by intratesticular route and sacrificed at 24h, 48h, 96h, 1, 2, 4, 8 and 11 weeks of infection and compared to 40 noninfected hamsters employed as controls. These animals were submitted to the study of NK cytotoxic activity by a single-cell assay and humoral immune response by immunodiffusion and ELISA tests. The production of macrophage migration inhibitory factor in the presence of Phyto-hemagglutinin and P. brasiliensis antigen and histopathology of the lesions were evaluated at 1, 4, 8 and 11 weeks of infection. The infected animals displayed significantly high levels of NK activity during the four weeks of infection that decreased from the 8th week on when compared to controls. This impairment of NK activity was associated with depression of cell-mediated immune response and with increase in the extension of the histopathologic lesions. There was an inverse correlation between NK cell activity and specific antibody levels. The results suggest that after initial activation, NK cells were unable to control the fungus dissemination. The impairment of NK activity in the late stages of the infection might be related to immunoregulatory disturbances associated with paracoccidioidomycosis.

Persistence of specific antibody response in different experimental infections of mice with Toxocara canis larvae

Anti-Toxocara antibody production and persistence were studied in experimental infections of BALB/c mice, according to three different schedules: Group I (GI) - 25 mice infected with 200 T. canis eggs in a single dose; Group II (GII) 25 mice infected with 150 T. canis eggs given in three occasions, 50 in the 1st, 50 in the 5th and 50 in the 8th days; Group III (GIII) - 25 mice also infected with 150 T. canis eggs, in three 50 eggs portions given in the 1st, 14th and 28th days. A 15 mice control group (GIV) was maintained without infection. In the 30th, 50th, 60th, 75th, 105th and 180th post-infection days three mice of the GI, GII and GIII groups and two mice of the control group had been sacrificed and exsanguinated for sera obtention. In the 360th day the remainder mice of the four groups were, in the same way, killed and processed. The obtained sera were searched for the presence of anti-Toxocara antibodies by an ELISA technique, using T. canis larvae excretion-secretion antigen. In the GI and GII, but not in the GIII, anti-Toxocara antibodies had been found, at least, up to the 180th post-infection day. The GIII only showed anti-Toxocara antibodies, at significant level, in the 30th post-infection day.

Entamoeba histolytica: fecal antigen capture immunoassay for the diagnosis of enteric amebiasis by a monoclonal antibody

Amebiasis continues to be of epidemiological importance in underdeveloped countries. Clinical diagnosis and epidemiological setting in a region are based on the fecal microscopic identification of cysts or trophozoites. This procedure requires well trained personnel, is laborious, of low sensitivity and frequently yields false-positives results. The present study was designed to develop an immuno-enzymatic fecal 96 kDa antigen capture test (COPROELISA-Eh) more sensitive and specific than microscopic diagnosis of amebiasis. Triplicates of 177 stool samples processed by the formol-ether concentration method, were defined as positive or negative by three experienced microscopic observers. Another aliquot was submitted to the antigen capture test by a monoclonal antibody against a specific membrane antigen of pathogenic strains of Entamoeba histolytica. Optical densities were interpreted as positive when they exceeded the mean value of negative samples plus two standard deviations. COPROELISA-Eh showed a 94.4% sensitivity, 98.3% specificity, 96.2% positive predictive value and 97.6% negative predictive value for the detection of E. histolytica in feces. COPROELISA-Eh is more sensitive and specific than microscopic examination, does not require specially trained personnel and allows the simultaneous processing of a large number of samples.

Measles antibody prevalence after mass immunization campaign in Niterói, State of Rio de Janeiro, Brazil

Three months after a mass vaccination campaign (coverage: 100%) against measles a random seroepidemiological survey was carried out in students aged 1 to 19 years old in the Municipality of Niterói, State of Rio de Janeiro. Blood samples were tested for measles antibodies by enzyme immunosorbent assay (EIA) and negative cases were tested again using hemagglutination inhibition (HI) and plaque reduction neutralization (PRN). Of the 798 samples tested by EIA, 718 (90.2%) were positive for measles antibodies. PRN test was more sensitive than EIA and HI in detecting measles specific antibodies. The total antibody prevalence increased from 90.2% to 93.2% when HI was employed in EIA negative specimens and to 98.9% when PRN was used. After the mass vaccination campaign a marked decrease in measles incidence was observed in the municipality studied, showing the effectiveness of the strategy used for measles control in developing countries.

Effect of b-Propiolactone treatment on the complement activation mediated by equine antisera

Reduction of complement activation through an alteration of the Fc fragment of immunoglobulins by b-propiolactone treatment was carried out in equine antisera raised against rabies virus, Bothrops venoms and diphtherial toxin. Results were evaluated by means of an anaphylactic test performed on guinea-pigs, and compared to the ones obtained with the same sera purified by saline precipitation (ammonium sulfate), followed or not by enzymatic digestion with pepsin. Protein purity levels for antibothropic serum were 184.5 mg/g and 488.5 mg/g in b-propiolactone treated and pepsin-digested sera, respectively. The recovery of specific activity was 100% and 62.5% when using antibothropic serum treated by b-propiolactone and pepsin digestion, respectively. The antidiphtherial and anti-rabies sera treated with b-propiolactone and pepsin presented protein purity levels of 5,698 and 7,179 Lf/g, 16,233 and 6,784 IU/g, respectively. The recovery of specific activity for these antisera were 88.8%, 77.7%, 100% and 36,5%, respectively. b-propiolactone treatment induced a reduction in complement activation, tested "in vivo", without significant loss of biological activity. This treatment can be used in the preparation of heterologous immunoglobulins for human use.

Decay of antibody isotypes against early developmental stages of Schistosoma mansoni after treatment of schistosomiasis patients

Antibodies to a number of parasite antigens are found in schistosomiasis patients, and antibodies to early developmental stages were demonstrated to be efficient immunologic markers for the diagnosis of schistosomiasis. In the present study, decay patterns of IgM and IgG antibodies against cercariae and schistosomula were investigated, in comparison to antibodies against worms and eggs in schistosomiasis patients after chemotherapy, for an investigation of seroepidemiologic aspects. Data obtained in the study of 359 serum samples from patients with Schistosoma mansoni infection, noninfected individuals, and patients followed-up for a period of 12 to 15 months after treatment provided the basis to postulate a general pattern for the kinetics of antibody decay. Before treatment, the antibody pattern was represented by a unimodal curve, which shifted to a bimodal curve after treatment, and ended with a unimodal curve similar to that for the noninfected group. Different types of antibodies were classified into four categories according to their decay features, and anti-schistosomulum IgM was classified into the moderate-decay caterogy, whereas other antibodies to early parasite stages were classified into the slow-decay category. The present methodology permits the identification of the most suitable antibodies to be detected in field control programs for schistosomiasis or other parasitoses