We have previously shown that a mixture of three synthetic peptides (83.1, 55.1, 35.1), corresponding to fragments of the relative molecular mass 83,000 (83K), 55K and 35K Plasmodium falciparum merozoite-specific proteins, induces protection in Aotus triviroatus monkeys experimentally infected with P. falciparum. Here we describe two polymeric synthetic hybrid proteins based on these peptides that delay or suppress the development of parasitaemia in immunized human volunteers.

To determine amino acid sequences of the Plasmodium falciparum MSP-1 protein that interact with red blood cell membranes in a specific receptor-ligand interaction, 78 sequential peptides, 20 amino acids long and spanning the entire length of the molecule, were synthesized and analysed with a specific binding assay developed for this purpose. Results show that peptides based on conserved and dimorphic regions of MSP-1, interact with human red blood cells (RBCs). This interaction occurs predominantly with peptides contained within the MSP-1 proteolytic fragments of 83 kDa, 38 kDa, 33 kDa and 19 kDa. Affinity constants of these peptides were between 140 and 250 nM. Peptide-RBC binding post enzyme treatment showed that the RBC receptors are not sialic acid dependent and appear to be proteic in nature. Some of these peptides inhibited merozoite invasion of RBCs yet did not inhibit intraerthrocytic development. These peptides, in conjunction with those from other merozoite surface proteins, may be used to rationally design a second generation of synthetic peptide-based malaria vaccines.

Abbreviations:CD 280synthesis is probably the way to go, since the good properties of each technology can be synergistically used in the context of one process objective.Peptides are heteropolymers composed by amino acid residues linked by peptidic bonds between the carboxyl group of one amino acid residue and the α-amino group of the next one. The definition is rather vague in terms of chain length, peptides ranging from two to a few dozens residues. Its lower limit of molecular mass has been set rather arbitrarily in 6000 Da; molecules larger than that are considered proteins. Peptides are molecules of paramount importance in several fields, especially in health care and nutrition. The case of the hormone insulin (51 residues, 5773 Da) and the non-caloric sweetener aspartame (a dipeptide of aspartic acid and esterified phenylalanine) are relevant examples of those fields of application and the range of molecular size. Medium to small size peptides are, however, the most relevant for such applications.

Synthetic peptides are potential vaccine candidates because they may be able to induce high antibody titres and specific cellular immune responses against native proteins and thus the whole invading organism. In a previous study we showed that immunization with molecules of relative molecular mass (Mr) 155,000 (155K) 83K, 55K and 35K, specific for the late schizont and merozoite stages of Plasmodium falciparum, could elicit either partial or total protection in Aotus trivirgatus monkeys experimentally infected with P. falciparum. Here we have chemically synthesized 18 peptides corresponding to different fragments of these proteins to immunize Aotus trivirgatus monkeys. Some peptides gave partial protection from challenge with P. falciparum parasites, but none provided complete protection individually. A combination of three partially protective peptides gave complete or almost complete protection, however, suggesting that this particular combination of peptides is a good candidate for a malaria vaccine.

Solid experimental evidence indicates that EBA-175 is used as a ligand by the Plasmodium falciparum merozoite to bind to human RBC, via different binding processing fragments. Using synthetic peptides and specific receptor-ligand interaction methodology, we have identified 6 high-activity binding sequences from the EBA-175 CAMP strain; peptide 1758 (KSYGTPDNIDKNMSLIHKHN), located in the so-called region I for which no binding activity has been reported before, peptides 1779 (NIDRIYDKNLLMIKEHILAI) and 1783 (HRNKKNDKLYRDEWWKVIKK), located in region II, in a sub-region known as 5' Cys F2, previously reported as being a binding region, and peptides 1814 (DRNSNTLHLKDYRNEENERH), 1815 (YTNQNINISQERDLQKHGFH) and 1818 (NNNFNNIPSRYNLYDKKLDL), in region III-V where antibodies inhibit merozoite invasion of erythrocytes. The affinity constants were between 60 and 180 nM and the critical amino acids involved in the binding were identified. The binding of these peptides to enzyme-treated RBC was analysed; binding of peptide 1814, located in the III-V region, was found to be sialic acid dependent. Some of these high binding peptides were able to inhibit in vitro merozoite invasion and to block the binding of recombinant RII-EBA to RBC. Several of these peptides are located in regions recognized by protective immune clusters of merozoites (ICMs) eluted antibodies.

T-cell molecular mimicry between streptococcal and heart proteins has been proposed as the triggering factor leading to autoimmunity in rheumatic heart disease (RHD). We searched for immunodominant T-cell M5 epitopes among RHD patients with defined clinical outcomes and compared the T-cell reactivities of peripheral blood and intralesional T cells from patients with severe RHD. The role of HLA class II molecules in the presentation of M5 peptides was also evaluated. We studied the T-cell reactivity against M5 peptides and heart proteins on peripheral blood mononuclear cells (PBMC) from 74 RHD patients grouped according to the severity of disease, along with intralesional and peripheral T-cell clones from RHD patients. Peptides encompassing residues 1 to 25, 81 to 103, 125 to 139, and 163 to 177 were more frequently recognized by PBMC from RHD patients than by those from controls. The M5 peptide encompassing residues 81 to 96 [M5(81-96) peptide] was most frequently recognized by PBMC from HLA-DR7 ؉ DR53 ؉ patients with severe RHD, and 46.9% (15 of 32) and 43% (3 of 7) of heart-infiltrating and PBMC-derived peptide-reactive T-cell clones, respectively, recognized the M5(81-103) region. Heart proteins were recognized more frequently by PBMC from patients with severe RHD than by those from patients with mild RHD. The similar pattern of T-cell reactivity found with both peripheral blood and heart-infiltrating T cells is consistent with the migration of M-protein-sensitized T cells to the heart tissue. Conversely, the presence of heart-reactive T cells in the PBMC of patients with severe RHD also suggests a spillover of sensitized T cells from the heart lesion.Rheumatic fever (RF) is a sequel of group A streptococcal throat infection and remains an important health problem in developing countries. About 30% of RF patients develop rheumatic heart disease (RHD), with high morbidity and cost to the public health system. Molecular mimicry between streptococcal antigens, mainly the M protein, and heart tissue proteins is proposed as an important factor leading to the heart lesions found in RHD patients. Several studies have been performed with human peripheral blood mononuclear cells (PBMC) showing reactivity against the streptococcal cell wall and tissue antigens (20,25). CD4 ϩ T cells are the predominant population at the site of heart lesions (23, 16).Yoshinaga et al. (30) reported that T-cell lines derived from heart valve specimens and PBMC from RF patients react with cell wall and membrane streptococcal antigens. These lymphocytes did not cross-react with M protein or mammalian cytoskeletal proteins. Autoreactivity to heart antigens caused by streptococcal infections was also suggested by results of immunization in which peripheral T lymphocytes from RHD patients stimulated in vitro with streptococci were able to recognize a 50-to 54-kDa myocardial protein fraction (7). Our group previously reported intralesional T-cell clones, from surgical fragments of patients with severe RHD, capable of recognizing immunodominant...

Clinical trials of malaria vaccines have confirmed that parasite-derived T-cell epitopes are required to elicit consistent and long-lasting immune responses. We report here the identification and functional characterization of six T-cell epitopes that are present in the merozoite surface protein-1 of Plasmodium vivax (PvMSP-1) and bind promiscuously to four different HLA-DRB1‫ء‬ alleles. Each of these peptides induced lymphoproliferative responses in cells from individuals with previous P. vivax infections. Furthermore, linear-peptide chimeras containing the promiscuous PvMSP-1 T-cell epitopes, synthesized in tandem with the Plasmodium falciparum immunodominant circumsporozoite protein (CSP) B-cell epitope, induced high specific antibody titers, cytokine production, long-lasting immune responses, and immunoglobulin G isotype class switching in BALB/c mice. A linear-peptide chimera containing an allele-restricted P. falciparum T-cell epitope with the CSP B-cell epitope was not effective. Two out of the six promiscuous T-cell epitopes exhibiting the highest antipeptide response also contain B-cell epitopes. Antisera generated against these B-cell epitopes recognize P. vivax merozoites in immunofluorescence assays. Importantly, the anti-peptide antibodies generated to the CSP B-cell epitope inhibited the invasion of P. falciparum sporozoites into human hepatocytes. These data and the simplicity of design of the chimeric constructs highlight the potential of multimeric, multistage, and multispecies linear-peptide chimeras containing parasite promiscuous T-cell epitopes for malaria vaccine development.

In the last decades, the indiscriminate use of conventional antibiotics has generated high rates of microbial resistance. This situation has increased the need for obtaining new antimicrobial compounds against infectious diseases. Among these, antimicrobial peptides (AMPs) constitute a promising alternative as therapeutic agents against various pathogenic microbes. These therapeutic agents can be isolated from different organisms, being widespread in nature and synthesized by microorganisms, plants and animals (both invertebrates and vertebrates). Additionally, AMPs are usually produced by a non-specific innate immune response. These peptides are involved in the inhibition of cell growth and in the killing of several microorganisms, such as bacteria, fungi, enveloped viruses, protozoans and other parasites. They have many interesting properties as potential antibiotics, such as relatively small sizes (below 25-30 kDa), amphipathic structures, cationic nature, and offer low probability for the generation of microbial resistance. In recent years, many novel AMPs, with very promising therapeutic properties, have been discovered. These peptides have been the base for the production of chemical analogs, which have been designed, chemically synthesized and tested in vitro for their antimicrobial activity. This review is focused on antibacterial (against Gram (-) and Gram (+) bacteria) and antifungal peptides, discussing action mode of AMPs, and recent advances in the study of the molecular basis of their anti-microbial activity. Finally, we emphasize on their current pharmacological development, future directions and applications of AMPs as promising antibiotics of therapeutic use for microbial infections.