Search PubMed⌕ Search

Biomedical subjects

C M Gontijo

Publications and source records attributed to C M Gontijo.

At least 19 recordsLinked to original sources
PubMed2002

Covalent coupling of palmitate to ovalbumin inhibits and blocks the induction of oral tolerance.

Oral tolerance is a phenomenon that may occur in animals exposed to soluble antigens for the first time by the oral route. In the present study, we show that oral tolerance against ovalbumin (Ova) can be obtained after intragastric administration of the antigen in the presence of free residues of palmitate. On the other hand, oral tolerance induction is blocked when the residues of palmitate are covalently bound to the antigen (Ova-palmitate conjugates). We have also noticed that oral administration of Ova-palmitate conjugates can boost and/or prime experimental animals for Ova-specific cellular and humoral systemic immune responses. Oral treatment with the conjugates also induces the production of local secretory immunoglobulin A (IgA) as measured in intestinal washes. Furthermore, Ova-palmitate given orally can inhibit oral tolerance induction by naïve Ova.

Administration, Oral↗
PubMed2001

Visceral leishmaniasis in the Metropolitan Region of Belo Horizonte, State of Minas Gerais, Brazil.

In the last few years the number of human cases of American visceral leishmaniasis in the Metropolitan Region of Belo Horizonte (MRBH), Minas Gerais, Brazil has increased, indicating an elevation in the transmission rate of the disease. The total number of notified human cases in the MRBH since 1994, when the first case was identified, up to 1999 was 345 of which 223 (65%) were from the city itself, indicating an urbanization of the disease in this region of Minas Gerais. The age distribution of visceral leishmaniasis cases in the MRBH shows a higher prevalence in children from 0-4 years old, responsible for 28.9% of the notifications. Clinical and immunological findings from dogs infected with Leishmania chagasi are described. The majority of these animals showed no sign of the disease. Sera from all infected dogs showed detectable Leishmania-induced high titles of antibodies based on the results of an indirect fluorescent antibody test. Samples of isolated Leishmania from human and dogs were characterized as L. (L.) chagasi by biochemical and molecular techniques.

Adolescent↗
PubMed2001

Short report: detection of Leishmania DNA by polymerase chain reaction on blood samples from dogs with visceral leishmaniasis.

Immunological, parasitological, and molecular techniques were applied to blood samples of dogs to diagnose Leishmania infections. In 1997, 644 domestic dogs were studied. Peripheral blood samples were collected for serological diagnosis and detection of Leishmania parasite by polymerase chain reaction (PCR). The indirect immunofluorescence test was positive in 139 (21.6%) of 644 dogs examined. The PCR was performed in 70 blood samples and 3 bone marrow aspirates. A 120-bp fragment specific for Leishmania was present in PCR hybridization analysis of all seropositive samples in the molecular assays. The PCR hybridization test, which used a minicircle of Leishmania chagasi as a probe, was negative in 20 seronegative dogs. These results suggest that a combined PCR-Southern hybridization technique is a highly sensitive approach to diagnose leishmaniasis in dogs, which are a zoonotic reservoir of leishmaniasis for humans.

Animals↗
PubMed1999

Leishmania (Viannia) braziliensis is the predominant species infecting patients with American cutaneous leishmaniasis in the State of Minas Gerais, Southeast Brazil.

Skin biopsies from 53 patients with American cutaneous leishmaniasis (ACL) from the State of Minas Gerais, Brazil, were used for a characterization of the Leishmania parasites. A pair of primers flanking the conserved region of the Leishmania minicircle kDNA was used to obtain amplified DNA via the polymerase chain reaction. The amplified products were subsequently hybridized with Leishmania subgenus-specific radiolabeled probes. Parasites from 49 out of 53 samples (92.5%) were characterized as belonging to the subgenus Viannia and four (7.5%) as belonging to the subgenus Leishmania. Clinical, epidemiological and molecular evidence allow us to conclude that Leishmania (V.) braziliensis and Leishmania (L.) amazonensis are the species present in the patients studied and that L. (V.) braziliensis is the predominant species in the State of Minas Gerais, Brazil.

Adolescent↗
PubMed1999

Immunization by subcutaneous implants of polyester-polyurethane sponges coupled with antigen.

A new protocol is described for immunization of outbred Swiss mice. The procedure is based on subcutaneous implantation of antigen-coupled polyester-polyurethane sponges cut into disks of 10 mm in diameter vs 2 mm in thickness. Antigen coupling was performed by overnight incubation of the sponge with a solution of ovalbumin (Ova) (2 mg/ml) diluted in sodium carbonate buffer, pH 9.6. The amount of ovalbumin that was taken up by the sponge was between 71.4 to 82.5 micrograms. This was estimated by comparing the Ova absorbance at 280 nm in coating buffer solutions before and after incubation. To compare the efficiency of the proposed method, experimental groups immunized with the antigen in the presence of adjuvants (10 micrograms in Al(OH)3 or 100 micrograms in complete Freund's adjuvant (CFA)) were run in parallel. The data obtained after the 3rd week of immunization indicate that both cellular and humoral immune responses were achieved. These were assayed by antigen-induced footpad swelling and ELISA (specific antibodies), respectively. The levels of both immune responses elicited were similar to the responses observed in mice immunized with ovalbumin in the presence of Al(OH)3. The method might represent an advantage when immunizing with pathogenic antigens. Preliminary experiments have suggested that the antigen remains immobilized or bound to the sponge for a long period of time, since there is an increment on the cell population inside the sponges after boosting the animals. If so, the undesirable effects of immunization would be reduced.

Animals↗
PubMed1998

Coupling of palmitate to ovalbumin inhibits the induction of oral tolerance.

Oral tolerance is a phenomenon that may occur in animals exposed to protein antigens for the first time by the oral route. They become unable to produce immune responses at the levels normally observed when they are immunized parenterally with antigen in the presence of adjuvants. Lipids have been used as adjuvants for both parenteral and oral immunization. In the present study we coupled ovalbumin with palmitate residues by incubating the protein with the N-hydroxysuccinimide palmitate ester and tested the preparation for its ability to induce oral tolerance. This was performed by giving 20 mg of antigen to mice by the oral route 7 days prior to parenteral immunization in the presence of A1(OH)3. Mice were bled one week after receiving a booster that was given 2 weeks after primary immunization. Specific antibodies were detected by ELISA. Despite the fact that the conjugates are as immunogenic as the unmodified protein when parenterally injected in mice, they failed to induce oral tolerance. This discrepancy could be explained by differences in the intestinal absorption of the two forms of the antigen. In fact, when compared to the non-conjugated ovalbumin, a fast and high absorption of the lipid-conjugated form of ovalbumin was observed by "sandwich" ELISA.

Animals↗
PubMed1993

Membrane-incorporated surrogate receptors increase antigen presentation by resting B cells, but not by LPS-activated blasts.

Palmitate-conjugated monoclonal antibodies specific to ovalbumin were inserted into the cell membrane of normal resting B cells and LPS-activated blasts. These two decorated B cells were tested for their ability to act as antigen-presenting cells for ovalbumin-specific I-Ad-restricted T-cell hybridomas. It was found that the antibody-decorated resting B cells presented antigen more efficiently than non-decorated controls. However, no increment was observed when decorated LPS blasts were compared with non-decorated blasts. This is explained by the fact that the inserted antibodies quickly disappeared from the cell membrane of LPS blasts, while they were retained for a long period in the membrane of resting B cells.

Animals↗
PubMed1993

B cells carrying surrogate receptors in their membranes process and present antigen to specific murine T cells.

A palmitate-conjugate derivative of ovalbumin which can be inserted into the membrane of B cells has been prepared. The ability of these cells to act as antigen-presenting cells for specific T lymphocytes obtained from immunized mice was tested. It was found that the conjugates were more efficiently processed and presented than the naive form of the antigen. Palmitate-conjugated antibodies specific to ovalbumin were also inserted into the cell membrane of normal B lymphocytes. These cells were pulsed with the antigen and tested as antigen-presenting cells for T cells obtained from immunized mice. The antibody-decorated B cells presented ovalbumin more efficiently than non-decorated controls. Whether antibody-decorated, antigen-pulsed B cells could prime T cells in vivo was investigated. Some priming activity was found.

Animals↗
PubMed1992

Increasing the efficiency of lipid-conjugated antibodies incorporation into the membrane of antigen presenting B cells.

We have introduced some modifications in the technique called "cell decoration" in order to increase the amount of lipid-conjugated antibodies which can be incorporated into the membrane of B cells. As shown by FACS analysis, we have obtained an approximately 4-fold increment in the amount of specific antibodies incorporated into the cell membrane. The procedure, which consists of successive changes of the medium that contains the lipid-conjugated antibodies, avoided changes on parameters that interfere with cell viability. The proposed modification resulted in an approximately 2-fold enhancement of the ability of decorated B cells to act as antigen presenting cells for specific T hybridomas.

Animals↗
PubMed1991

Antigen processing and presentation by small and large B cells.

We have investigated the ability of different cells from non-immunized mice of the BALB/c strain to present antigen to two ovalbumin-specific I-Ad-restricted T hybridomas. Lipopolysaccharide-activated B-cell blasts were found to be the most efficient antigen-presenting cells. Purified small and dense splenic B cells also stimulated the hybridomas, although not to the same extent as the activated blasts, but comparable to non-fractionated spleen cells. Glutaraldehyde-treated B cells failed to present antigen, whereas F(ab')2 anti-mouse IgM-treated B cells exhibited markedly increased ability to present antigen. Using flow cytometry, we further purified the resting B cells by sorting the small lymphocytes to ensure that the ability of these cells to activate the hybridomas was not due to contamination with large non-resting B cells. The sorted small B cells retained the ability of antigen presentation. Their resting state was confirmed by the fact that they did not incorporate [3H]-thymidine as shown by autoradiographic analysis.

Animals↗
PubMed1991

Membrane-incorporated immunoglobulin receptors increase the antigen-presenting ability of B cells.

Monoclonal antibodies specific for ovalbumin were conjugated to palmitate and inserted into the membrane of normal spleen B cells. Their presence in the membrane, as well as their ability to bind ovalbumin, was established by immunofluorescence. The so called anti-ovalbumin-'decorated' B cells were tested for their ability to act as antigen-presenting cells for ovalbumin-specific I-Ad-restricted T-cell hybridomas. It was found that the antibody-decorated B cells presented antigen more efficiently than non-decorated B cells.

Animals↗
PubMed1991

The immunoglobulin receptors on B cells bind antigen, focus activation signals to them and initiate antigen-presentation.

We do not agree with the analysis of Langman and Cohn on the function of Ig receptors. We have reviewed the available literature regarding anti-Ig activation of B cells and found it contradictory and unconvincing. We have presented experimental evidence on the inability of Ig receptors on B cells to mediate activation or tolerogenic signals. We suggest that the Ig receptors serve to focus antigen to specific B cells so the B cells can be activated by TI antigens or helper T cells. The Ig molecules also bind foreign antigen and thereby initiate internalization and antigen processing. The processed peptides are exported to the membrane, where they associate with MHC class II antigens, thus transforming B cells into efficient antigen-presenting cells.

Animals↗
PubMed1988

Tolerance induction and immunological priming initiated by mucosal contacts with protein antigens in inbred strains of mice.

1. We show that mouse strains differ widely in susceptibility to tolerance induction and/or immunization (priming) following contact of protein antigens (ovalbumin, human or bovine gamma globulins) with different mucosal surfaces. 2. When compared to a control group pretreated with saline, mice pretreated by the oral (intragastric) route with antigen became significantly less responsive to subsequent parenteral immunization (i.e., tolerant). This was observed in most, but not all, antigen/strain combinations. 3. Similar, although less prominent changes were induced by pretreatments with antigen by the ocular (conjunctival) route. 4. No significant effects were observed following pretreatments by the nasal, vaginal or rectal routes. 5. Genes present in strains selected for multispecific "high" or "low" responsiveness are included among those involved in tolerance induction following mucosal contacts with protein antigens.

Animals↗
PubMed1987

Genetics of susceptibility to oral tolerance to ovalbumin.

Inbred mouse strains vary widely in their susceptibility to the induction of tolerance following oral (intragastric) administration of ovalbumin. Marked differences were found between strains that form a congenic pair differing at the H-2 complex: C3H/HeJ (H-2k) and C3H.SW (H-2b)-which were very susceptible and resistant to tolerance induction, respectively. In contrast, no significant differences were found between A/J (H-2a) and A.BY (H-2b) congenics, which were both susceptible, nor among C57BL/10J congenics, which were uniformly resistant to tolerance induction. We conclude that H-2-linked genes determine tolerance susceptibility in conjunction with background genes.

Administration, Oral↗
PubMed1983

Schistosoma mansoni: inhibition in vitro of granulocyte cytotoxicity against schistosomula by autologous mononuclear cells from patients.

Granulocytes and mononuclear cells from normal subjects are able to kill Schistosoma mansoni schistosomula in the presence of human complement in vitro. In contrast, mononuclear cells from chronic schistosomiasis patients failed to kill the parasites. The relative efficiencies expressed in terms of the mean percentage killing of schistosomula for 15 experiments were 50.5 +/- 3.2 and 49.7 +/- 3.5 for granulocytes from normal and infected patients, and 50.8 +/- 2.8 against 23.0 +/- 3.2 for mononuclear cells from normal and infected patients, respectively. The killing effect of granulocytes dropped from 48.7 +/- 2.8 to 22.1 +/- 2.2 when autologous mononuclear cells from chronically infected patients were added to the system. Similar inhibitory effect of granulocyte function was obtained when these cells were incubated with normal mononuclear cells precultured with concanavalin A. Extracts prepared from mononuclear cells obtained from infected patients had the same inhibitory effect of intact cells on the complement-dependent granulocyte cytotoxicity.

Complement System Proteins↗
PubMedDate not supplied

[Cutaneous leishmaniasis in the Metropolitan Region of Belo Horizonte: clinical, laboratorial, therapeutic and prognosis features (1989-1995)].

This study investigated clinical, laboratorial, therapeutic and prognostic aspects of American cutaneous leishmaniasis in Belo Horizonte in 358 patients with cutaneous leishmaniasis (CL) and 25 with mucocutaneous leishmaniasis (MCL). Compared to CL patients, the MCL patients reported longer duration of disease and higher frequency of other diseases, suggesting that debilitation caused by leishmaniasis or other conditions might contribute to activation and/or mucous dissemination of the parasite. The sensitivity of skin test, indirect immunofluorescence reactions and direct detection of parasites was 78.4, 79.3 and 68.3%, respectively. The treatment with meglumine antimoniate presented 100% efficacy, but 59% patients had side-effects. During two years of follow-up, there were 32/318 relapses after successful treatment. Most relapses (31/32) were of CL patients treated with 15 mg Sb5+/kg/day. The negative response to skin test was the only factor associated with a significant threefold increased risk of relapse. Higher dose or longer duration of treatment might improve the prognosis in these patients.

Adolescent↗