Evelyn Kety Pratt Riccio

Sera of patients with systemic lupus erythematosus react with plasmodial antigens and can inhibit the in vitro growth of Plasmodium falciparum.

The acquisition of protective immunity in malaria is a slow process during which autoantibodies are produced. The present work aimed at studying a possible interference of autoimmune responses on malaria immune protection. This was done by investigating the presence of autoantibodies in the sera of malarious patients, by searching for reactivity of autoantibodies from autoimmune patients against plasmodial antigens, and by studying the effect of such antibodies on the in vitro growth of Plasmodium falciparum. Sera from systemic lupus erythematosus (SLE) and malaria patients were tested against autologous and plasmodial antigens. Out of the 109 SLE sera tested, 48 (44%) reacted against the parasite. In addition, 26 (47%) out of 55 randomly selected sera, mainly those containing anti-DNA and antinuclear autoantibodies, were able to inhibit parasite growth to some extent. Conversely, a high frequency (81%) of sera of malaria patients exhibited reactivity against autoantigens. The results show that patients with autoimmune processes can produce antibodies that recognize plasmodial antigens in the absence of plasmodial infection, that malaria patients can produce autoantibodies, that SLE sera can inhibit plasmodial growth in vitro, and that the presence of anti-DNA and antinuclear antibodies may be important in such anti-plasmodial activity. It is concluded that autoimmune responses may have influence on the protective immunity against malaria.

Cryopreservation of peripheral blood mononuclear cells does not significantly affect the levels of spontaneous apoptosis after 24-h culture☆

Studies performed with malaria patients living in endemic areas are frequently conducted in laboratories located hundreds of kilometer away from research centers, due to the difficulties in performing the assays in field conditions. Thus, we considered the potential indication of cryopreservation of peripheral blood mononuclear cells (PBMC), in most fieldwork, and decided to evaluate the effect of cryopreservation of PBMC on spontaneous apoptosis. The membrane integrity of PBMC was tested using three previously described protocols of cryopreservation. Cell samples were obtained from 19 healthy volunteers. Percentage of apoptotic nuclei in short-term PBMC cultures was determined by a sensitive method using 7-aminoactinomycin D followed by flow cytometry. Our results indicate that although cryopreservation can to some extent affect lymphocyte membrane integrity rates, flow cytometry analysis showed that frequencies of spontaneous apoptosis in cryopreserved cells were not significantly modified after 24-h culture. It is concluded that cryopreserved PBMC could be used for measuring spontaneous apoptosis and therefore, could be employed for the study of populations living in areas distant from research centers, allowing the comparative evaluation of samples obtained at different time.

Dexamethasone has pro-apoptotic effects on non-activated fresh peripheral blood mononuclear cells.

Apoptosis is a physiological method of cell death commonly referred to as programmed cell death. However, non‐apoptotic programmed cell death, such as autophagy and programmed necrosis, has been characterized by morphological criteria. In view of the human therapeutic use of DEX, and considering that no difference in the number and/or affinity of glucocorticoid receptors in activated and non‐activated lymphocytes has been reported, we decided to evaluate the effect of DEX on fresh peripheral blood mononuclear cells (PBMC). Transmission electron microscopy showed that DEX can significantly induce apoptosis in non‐activated PBMC. It was also observed by transmission electron microscopy that, independently of DEX treatment, PBMC also died by a process marked by extreme vacuolization and increase in cellular volume; these cells were erroneously classified as viable by flow cytometry using the 7‐AAD assay. It is concluded that the DEX pro‐apoptotic effect is not restricted to activated PBMC and, therefore, DEX‐induced apoptosis could play either homeostatic (activated PBMC) or immunosuppressive (non‐activated PBMC) roles.

Antibodies against the Plasmodium falciparum glutamate-rich protein from naturally exposed individuals living in a Brazilian malaria-endemic area can inhibit in vitro parasite growth

The glutamate-rich protein (GLURP) is an exoantigen expressed in all stages of the Plasmodium falciparum life cycle in humans. Anti-GLURP antibodies can inhibit parasite growth in the presence of monocytes via antibody-dependent cellular inhibition (ADCI), and a major parasite-inhibitory region has been found in the N-terminal R0 region of the protein. Herein, we describe the antiplasmodial activity of anti-GLURP antibodies present in the sera from individuals naturally exposed to malaria in a Brazilian malaria-endemic area. The anti-R0 antibodies showed a potent inhibitory effect on the growth of P. falciparum in vitro, both in the presence (ADCI) and absence (GI) of monocytes. The inhibitory effect on parasite growth was comparable to the effect of IgGs purified from pooled sera from hyperimmune African individuals. Interestingly, in the ADCI test, higher levels of tumour necrosis factor alpha (TNF-α) were observed in the supernatant from cultures with higher parasitemias. Our data suggest that the antibody response induced by GLURP-R0 in naturally exposed individuals may have an important role in controlling parasitemia because these antibodies are able to inhibit the in vitro growth of P. falciparum with or without the cooperation from monocytes. Our results also indicate that TNF-α may not be relevant for the inhibitory effect on P. falciparum in vitro growth.

Increased Plasmodium falciparum Parasitemia in Non-splenectomized Saimiri sciureus Monkeys Treated with Clodronate Liposomes

A major constraint in the study of Plasmodium falciparum malaria, including vaccine development, lies on the parasites strict human host specificity and therefore the shortage of animal experimental models able to harbor human plasmodia. The best experimental models are neo-tropical primates of the genus Saimiri and Aotus, but they require splenectomy to reduce innate defenses for achieving high and consistent parasitemias, an important limitation. Clodronate-liposomes (CL) have been successfully used to deplete monocytes/macrophages in several experimental models. We investigated whether a reduction in the numbers of phagocytic cells by CL would improve the development of P. falciparum parasitemia in non-splenectomized Saimiri sciureus monkeys. Depletion of S. sciureus splenocytes after in vitro incubation with CL was quantified using anti-CD14 antibodies and flow cytometry. Non-infected and P. falciparum-infected S. sciureus were injected intravenously twice a week with either CL at either 0.5 or 1 mL (5 mg/mL) or phosphate buffered saline (PBS). Animals were monitored during infection and treated with mefloquine. After treatment and euthanasia, spleen and liver were collected for histological analysis. In vitro CL depleted S. sciureus splenic monocyte/macrophage population in a dose- and time-dependent manner. In vivo, half of P. falciparum-infected S. sciureus treated with CL 0.5 mL, and two-thirds of those treated with CL 1 mL developed high parasitemias requiring mefloquine treatment, whereas all control animals were able to self-control parasitemia without the need for antimalarial treatment. CL-treated infected S. sciureus showed a marked decrease in the degree of splenomegaly despite higher parasitemias, compared to PBS-treated animals. Histological evidence of partial monocyte/macrophage depletion, decreased hemozoin phagocytosis and decreased iron recycling was observed in both the spleen and liver of CL-treated infected S. sciureus. CL is capable of promoting higher parasitemia in P. falciparum-infected S. sciureus, associated with evidence of partial macrophage depletion in the spleen and liver. Macrophage depletion by CL is therefore a practical and viable alternative to surgical splenectomy in this experimental model.

Genetic polymorphism of the serine rich antigen N-terminal region in Plasmodium falciparum field isolates from Brazil

In this work we investigated the frequency of polymorphism in exon II of the gene encoding most of the amino-terminal region of the serine rich antigen (SERA) in Plasmodium falciparum field samples. The blood samples were collected from P. falciparum infected individuals in three areas of the Brazilian Amazon. Two fragments have been characterized by polymerase chain reaction: one of 175 bp corresponding to the repeat region with 5 octamer units and one other of 199 bp related to the 6 repeat octamer units of SERA protein. The 199 bp fragment was the predominant one in all the studied areas. The higher frequency of this fragment has not been described before and could be explained by an immunological selection of the plasmodial population in the infected individuals under study. Since repeat motifs in the amino-terminal region of SERA contain epitopes recognized by parasite-inhibitor antibodies, data reported here suggest that the analysis of the polymorphism of P. falciparum isolates in different geographical areas is a preliminary stage before the final drawing of an universal vaccine against malaria can be reached.

Synthetic Antigens Derived from Plasmodium falciparum Sporozoite, Liver, and Blood Stages: Naturally Acquired Immune Response and Human Leukocyte Antigen Associations in Individuals Living in a Brazilian Endemic Area

Peptide vaccine strategies using Plasmodium-derived antigens have emerged as an attractive approach against malaria. However, relatively few studies have been conducted with malaria-exposed populations from non-African countries. Herein, the seroepidemiological profile against Plasmodium falciparum of naturally exposed individuals from a Brazilian malaria-endemic area against synthetic peptides derived from vaccine candidates circumsporozoite protein (CSP), liver stage antigen-1 (LSA-1), erythrocyte binding antigen-175 (EBA-175), and merozoite surface protein-3 (MSP-3) was investigated. Moreover, human leukocyte antigen (HLA)-DRB1* and HLA-DQB1* were evaluated to characterize genetic modulation of humoral responsiveness to these antigens. The study was performed using blood samples from 187 individuals living in rural malaria-endemic villages situated near Porto Velho, Rondônia State. Specific IgG and IgM antibodies and IgG subclasses were detected by enzyme-linked immunosorbent assay, and HLA-DRB1* and HLA-DQB1* low-resolution typing was performed by PCR-SSP. All four synthetic peptides were broadly recognized by naturally acquired antibodies. Regarding the IgG subclass profile, only CSP induced IgG1 and IgG3 antibodies, which is an important fact given that the acquisition of protective immunity appears to be associated with the cytophilicity of IgG1 and IgG3 antibodies. HLA-DRB1*11 and HLA-DQB1*7 had the lowest odds of responding to EBA-175. Our results showed that CSP, LSA-1, EBA, and MSP-3 are immunogenic in natural conditions of exposure and that anti-EBA antibody responses appear to be modulated by HLA class II antigens.

Cellular and humoral immune responses against the Plasmodium vivax MSP-119 malaria vaccine candidate in individuals living in a Brazilian endemic area in northeastern Amazon

Background Plasmodium vivax Merozoite Surface Protein-1 (MSP-1) is an antigen considered to be one of the leading malaria vaccine candidates. PvMSP-1 is immunogenic and evidences suggest that it is a target for protective immunity against asexual blood stages of malaria parasites. This study aims to evaluate the acquired cellular and antibody immune responses against PvMSP-1 in individuals exposed to malaria infections in a Brazilian malaria endemic area.