The sequence of a third member of the heat shock protein family in Plasmodium falciparum

Preferential activation and expansion of human peripheral blood gamma delta T cells in response to Toxoplasma gondii in vitro and their cytokine production and cytotoxic activity against T. gondii-infected cells

Studies were conducted to determine if gamma delta T cells participate in the immune response to Toxoplasma gondii. Preferential expansion of human gamma delta T cells occurred when peripheral blood T cells from either T. gondii-seronegative or seropositive individuals were incubated with autologous PBMC infected with the parasite. That gamma delta T cells proliferated after incubation with infected cells was confirmed using purified of gamma delta T cells. These T. gondii-induced gamma delta T cell responses did not require prior exposure to the parasite since T cells obtained from umbilical cord blood from seronegative newborns also exhibited preferential expansion of gamma delta T cells. Cytofluorometric analysis of T cells obtained from either umbilical cord blood or peripheral blood from adults revealed that V gamma 9+ and V delta 2+ gamma delta T cells responded to stimulation with infected cells. Preferential expansion of gamma delta T cells was not restricted by polymorphic determinants of MHC molecules. PBMC that had internalized killed parasites but not PBMC incubated with T. gondii lysate antigens also stimulated preferential expansion and activation of gamma delta T cells as assessed by expression of CD25 and HLA-DR molecules. V gamma 9+V delta 2+ gamma delta T cells were cytotoxic for T. gondii-infected cells in an MHC-unrestricted manner, and produced IFN-gamma, IL-2, TNF-alpha, but not IL-4 when incubated with cells infected with the parasite. These results suggest that rapid induction of a remarkable primary gamma delta T cell response may be important in the early protective immune response to T. gondii.

Sequence, transcript characterization and polymorphisms of a Plasmodium falciparum gene belonging to the heat-shock protein (HSP) 90 family

A gene (pfhsp86) encoding a member of the heat-shock protein 90 (HSP90) family has been isolated from Plasmodium falciparum (Pf). The pfhsp86 coding region comprises two exons separated by an 0.8-kb intron with consensus splice junction sequences. The transcript itself is 3.4-kb long and includes a 0.65-kb 5'-untranslated region (UTR) and a 0.54-kb 3'-UTR. Upstream of the transcription start point (tsp) are putative promoter modules: an inverted CCAAT box, a G + C-rich sequence and several TATA sequences. Transcription is enhanced in in erythrocyte-stage parasites cultivated at elevated temperatures (2-3-fold at 39 degrees C and 3-4-fold at 41 degrees C). The pfhsp86 gene maps within a chromosome 7 segment that is linked to chloroquine (Cq) response in a Pf cross. The parents of this cross (Dd2, HB3) differ in the first exon by two trinucleotide repeats, while more divergence is apparent between the introns. These trinucleotide repeat differences are linked to Cq response in the HB3 x Dd2 cross, but they did not predict Cq response in nine Pf lines from different locations.

Hsp70 in parasites: as an inducible protective protein and as an antigen

The heat shock (HS) response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stresses. It has been demonstrated that heat shock proteins (HSP) play major roles in many cellular processes, and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology, from cancer research to interaction between host and parasites. This review deals with the hsp70 gene family and with its protein product, hsp70, as an antigen when pathogens infect humans. Members of HSP have been shown to be major antigens of many pathogenic organisms when they experience a major temperature shift upwards at the onset of infection and become targets for host B and T cells.

Two major phosphoproteins of Plasmodium falciparum are heat shock proteins

Two major phosphoproteins of Plasmodium falciparum could be identified by partial amino acid sequencing as the plasmodial members of the hsp 70 heat shock protein family, Pfhsp and Pfgrp. According to phosphoamino acid analyses of Pfhsp and Pfgrp isolated from [32P]orthophosphate-labeled malarial cultures, both proteins were phosphorylated in Ser and Thr. While Pfhsp contains higher amounts of labeled phosphoserine, Pfgrp contains higher amounts of phosphothreonine. Phosphorylation of both proteins increased throughout the entire erythrocytic growth cycle. At the trophozoite and schizont stages Pfhsp and Pfgrp are the most prominent phosphoproteins of Plasmodium falciparum. Using multiply redundant oligonucleotides directed against the N-terminus of Pfgrp we cloned and sequenced the entire Pfgrp gene. The gene encodes a product with a predicted length of 652 amino acids. The deduced amino acid sequence has identities of 65.5% and 65.0% to the human and rat grp78 proteins, respectively. Pfgrp possesses a classical N-terminal leader sequence. The published grp78 related gene sequences of Plasmodium falciparum are all fragments of the same plasmodial gene.

Plasmodium cynomolgi: the hsp 70 gene

The hsp 70 gene of Plasmodium cynomolgi was isolated and characterized. As expected the gene is highly similar to that of the hsp 70 gene of Plasmodium falciparum (98% at the protein level, 82% at the nucleotide level). Surprisingly, the hsp 70 gene appears to be present in a single copy in all the P. cynomolgi strains tested, a finding that has implications for the parasite's ability to undergo a heat shock response.

The biology of the heat shock response in parasites

The heat shock response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stress. It has been shown that heat shock proteins play major roles in many cellular processes and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology and from cancer research to interactions between host and parasite. In this review, Bruno Maresca and Luisella Carratu deal with some of the unique characteristics of the heat shock response in parasitic organisms.

Structure and possible function of heat-shock proteins in Falciparum malaria

Like many prokaryotes and eukaryotes, the malaria parasite also synthesizes several stress proteins. Most widely studied stress proteins of this parasite are the heat-shock proteins (hsps). Their discovery in malaria is a gift of recombinant DNA technology. Five hsp genes from Plasmodium falciparum have been identified which are located on different chromosomes. Thus the inheritance and expression of hsp genes are independent of each other. They share a large amount of sequence homology at N-terminus with the hsps of other organisms. Their gene regulatory sequences and other elements, important for gene expression, are yet to be determined. The biological role of these proteins in malaria is not fully understood but it is possible that they provide protection to the parasite from various stresses encountered in the host. In this process hsps probably bind to the toxic molecules as well as damaged proteins to flush them out of the parasite. Their involvement in the stage-specific parasite transformation to increase the infectivity and virulence, as observed in other parasites, remains to be determined. Malarial hsps are antigenic in humans. This antigenicity could be attributed to the non-homologous sequences in the C-terminus region. The potential of one of them (pfhsp 70I) for a future malaria vaccine and immunodiagnostics requires re-evaluation of the data.