Neutrophil alterations in pregnancy-associated malaria and induction of neutrophil chemotaxis by Plasmodium falciparum.

Pregnancy-associated malaria (PAM) is a severe form of the disease caused by sequestration of Plasmodium falciparum-infected red blood cells (iRBCs) in the developing placenta. Pathogenesis of PAM is partially based on immunopathology, with frequent monocyte infiltration into the placenta. Neutrophils are abundant blood cells that are essential for immune defence but may also cause inflammatory pathology. Their role in PAM remains unclear. We analysed neutrophil alterations in the context of PAM to better understand their contribution to disease development. Pregnant women exposed to Plasmodium falciparum had decreased numbers of circulating neutrophils. Placental-like BeWo cells stimulated with malaria parasites produced the neutrophil chemoattractant IL-8 and recruited neutrophils in a trans-well assay. Finally, immunostaining of a PAM placenta confirmed neutrophil accumulation in the intervillous space. Our data indicate neutrophils may play a role in placental malaria and should be more closely examined as an etiological agent in the pathophysiology of disease.

The path of malaria vaccine development: challenges and perspectives.

Malaria is a life-threatening disease caused by parasites of the Plasmodium genus. In many parts of the world, the parasites have developed resistance to a number of antimalarial agents. Key interventions to control malaria include prompt and effective treatment with artemisinin-based combination therapies, use of insecticidal nets by individuals at risk and active research into malaria vaccines. Protection against malaria through vaccination was demonstrated more than 30 years ago when individuals were vaccinated via repeated bites by Plasmodium falciparum-infected and irradiated but still metabolically active mosquitoes. However, vaccination with high doses of irradiated sporozoites injected into humans has long been considered impractical. Yet, following recent success using whole-organism vaccines, the approach has received renewed interest; it was recently reported that repeated injections of irradiated sporozoites increased protection in 80 vaccinated individuals. Other approaches include subunit malaria vaccines, such as the current leading candidate RTS,S (consisting of fusion between a portion of the P. falciparum-derived circumsporozoite protein and the hepatitis B surface antigen), which has been demonstrated to induce reasonably good protection. Although results have been encouraging, the level of protection is generally considered to be too low to achieve eradication of malaria. There is great interest in developing new and better formulations and stable delivery systems to improve immunogenicity. In this review, we will discuss recent strategies to develop efficient malaria vaccines.

Quinolinic alkaloids from Galipea longiflora Krause suppress production of proinflammatory cytokines in vitro and control inflammation in vivo upon Leishmania infection in mice.

An antileishmanial activity of quinolinic alkaloids from Galipea longiflora Krause, known as Evanta, has been demonstrated. We have previously shown that, apart from its leishmanicidal effect, in vitro pretreatment of spleen cells with an alkaloid extract of Evanta (AEE) interfered with the proliferation and interferon-γ production in lymphocytes polyclonally activated either with concanavalin A or anti-CD3. In the present study, we investigated if AEE could interfere with antigen-specific lymphocyte activation. We found that in vitro and in vivo treatment reduced recall lymphocyte responses, as measured by IFN-γ production (55% and 63% reduction compared to untreated cells, respectively). Apart from IFN-γ, the production of IL-12 and TNF was also suppressed. No effects were observed for meglumine antimoniate (SbV), the conventional drug used to treat leishmaniasis. When mice infected with Leishmania braziliensis promastigotes in the hind footpad were treated with AEE, the dynamics of the infection changed and the footpath thickness was efficiently controlled. The parasite load was also reduced but to a lesser extent than upon treatment with SbV. Combined treatment efficiently controlled both the thickness and parasite load as smaller lesions during the entire course of the infection were seen in the mice treated with AEE plus SbV compared with AEE or SbV alone. We discuss the benefits of combined administration of AEE plus SbV.

FcγRIIa polymorphism and anti-malaria-specific IgG and IgG subclass responses in populations differing in susceptibility to malaria in Burkina Faso.

FcγRIIa is known to be polymorphic; and certain variants are associated with different susceptibilities to malaria. Studies involving the Fulani ethnic group reported an ethnic difference in FcγRIIa-R131H genotype frequencies between the Fulani and other sympatric groups. No previous studies have addressed these questions in Burkina Faso. This study aimed to assess the influence of FcγRIIa-R131H polymorphism on anti-falciparum malaria IgG and IgG subclass responses in the Fulani and the Mossi ethnic groups living in Burkina Faso. Healthy adults more than 20 years old belonging to the Mossi or the Fulani ethnic groups were enrolled for the assessment of selected parasitological, immunological and genetic variables in relation to their susceptibility to malaria. The prevalence of the Plasmodium falciparum infection frequency was relatively low in the Fulani ethnic group compared to the Mossi ethnic group. For all tested antigens, the Fulani had higher antibody levels than the Mossi group. In both ethnic groups, a similar distribution of FcγRIIa R131H polymorphism was found. Individuals with the R allele of FcγRIIa had higher antibody levels than those with the H allele. This study confirmed that malaria infection affected less the Fulani group than the Mossi group. FcγRIIa-R131H allele distribution is similar in both ethnic groups, and higher antibody levels are associated with the FcγRIIa R allele compared to the H allele.

A malaria serological map indicating the intersection between parasite antigenic diversity and host antibody repertoires.

A malaria vaccine targeting Plasmodium falciparum remains a strategic goal for malaria control. If a polyvalent vaccine is to be developed, its subunits would probably be chosen based on immunogenicity (concentration of elicited antibodies) and associations of selected antigens with protection. We propose an additional possible selection criterion for the inclusion of subunit antigens; that is, coordination between elicited antibodies. For the quantitative estimation of this coordination, we developed a malaria serological map (MSM). Construction of the MSM was based on three categories of variables: (i) malaria antigens, (ii) total IgG and IgG subclasses, (iii) different sources of plasma. To validate the MSM, in this study, we used four malaria antigens (AMA1, MSP2-3D7, MSP2-FC27 and Pf332-C231) and re-grouped the plasma samples into five pairs of subsets based on age, gender, residence, HbAS and malaria morbidity in 9 years. The plasma total IgG and IgG subclasses to the test antigens were measured, and the whole material was used for the MSM construction. Most of the variables in the MSM were previously tested and their associations with malaria morbidity are known. The coordination of response to each antigens pair in the MSM was quantified as the correlation rate (CR = overall number of significant correlations/total number of correlations × 100 %). Unexpectedly, the results showed that low CRs were mostly associated with variables linked with malaria protection and the antigen eliciting the least CRs was the one associated with protection. The MSM is, thus, of potential value for vaccine design and understanding of malaria natural immunity.

[Humoral immune anti-Plasmodium falciparum AMA1 and MSP1 response in two ethnic groups living in sympatry in Mali]. / Réponse humorale anti-Plasmodium falciparum AMA1 et MSP1 dans deux groupes ethniques vivant en sympatrie au Mali.

Fulani of Mali are known for their lower susceptibility to Plasmodium falciparum malaria than their neighbours, the Dogon, despite similar transmission conditions. However, the mechanisms underlying these differences are poorly understood, particularly those concerning antigenspecific immune responses. The Apical Membrane Antigen 1 (AMA1) and the Merozoite Surface Antigen 1 (MSP1) are two malaria vaccine candidates, which play a pivotal role during the invasion of parasites into erythrocytes, and in the case of AMA1, of hepatocytes. Therefore, we analyzed the level of anti-AMA1 and anti-MSP1 antibodies (FVO and 3D7 alleles), by using ELISA (Enzyme Linked Immuno Sorbent Assay) to investigate whether there are differences between the two ethnic groups. Our results show that the splenic rate, the level of anti-AMA1 and anti-MSP1 were significantly higher in Fulani compared to Dogon; while the parasite rate was lower in Fulani group compared to Dogon. Our results suggest that the lower susceptibility of Fulani to malaria could be due to the higher specific humoral responses against AMA1 and MSP 1 in Fulani's ethnic group compared to Dogon.

Pattern of pre-existing IgG subclass responses to a panel of asexual stage malaria antigens reported during the lengthy dry season in Daraweesh, Sudan.

The anti-malarial IgG immune response during the lengthy and dry season in areas of low malaria transmission as in Eastern Sudan is largely unknown. In this study, ELISA was used for the measurement of pre-existing total IgG and IgG subclasses to a panel of malaria antigens, MSP2-3D7, MSP2-FC27, AMA-1 and Pf332-C231. The results showed that the antibody responses were predominantly age dependent, antigen specific, and their lifespan was at least 5-6 month long. Generally, the IgG3 was most abundant IgG subclass, and the most recognized antigen was Pf332-C231. Furthermore, the correlation between the levels of IgG subclasses was strongest between IgG1 and IgG3, which were more predictive to the total IgG levels. Finally, the response pattern of each of the IgG subclasses to the different test antigens that were spanning the dry season and the correlation between these responses were described in details for the first time.

Antibodies to the Plasmodium falciparum rhoptry protein RAP-2/RSP-2 in relation to anaemia in Cameroonian children.

Previous studies have implicated reactive antibodies to the low molecular weight rhoptry-associated proteins (RAP-1, RAP-2/RSP-2 and RAP-3) in erythroid cell destruction during Plasmodium falciparum infection. In this pilot study, the frequency, specificity and functional capacity of naturally acquired anti-RAP-2/RSP-2 antibodies were investigated in the sera of anaemic and nonanaemic malaria-infected Cameroonian children. All sera recognized RAP-2/RSP-2 by FACS, irrespective of the clinical status of the subjects. However, the anaemic children showed higher levels of IgG antibodies than the nonanaemic group, while both groups showed similar levels of IgM antibodies. Only few individuals had detectable levels of RAP-2/RSP-2-specific IgG1 and IgG3 subclass antibodies, while no IgG2 and IgG4 subclass antibodies were detected in these subjects. By ELISA, the anaemic group tended to show higher levels of antibodies to RAP-2/RSP-2 regarding all antibody classes tested, except for IgG4 and IgE. Unexpectedly, sera from the nonanaemic group activated complement to a greater extent than those from the anaemic group. These results need to be confirmed in extended studies but indicate that the effector functions of the RAP-2/RSP-2-reactive antibodies may be more important than their amounts. Such antibodies could play a role in both immunity and pathogenesis during P. falciparum infection.

Resistance of natural killer T cell-deficient mice to systemic Shwartzman reaction.

The generalized Shwartzman reaction in mice which had been primed and challenged with lipopolysaccharide (LPS) depends on interleukin (IL)-12-induced interferon (IFN)-gamma production at the priming stage. We examined the involvement in the priming mechanism of the unique population of Valpha14 natural killer T (NKT) cells because they promptly produce IFN-gamma after IL-12 stimulation. We report here that LPS- or IL-12-primed NKT cell genetically deficient mice were found to be resistant to LPS-elicited mortality. This outcome can be attributed to the reduction of IFN-gamma production, because injection of recombinant mouse IFN-gamma, but not injection of IL-12, effectively primed the NKT cell-deficient mice. However, priming with high doses of LPS caused mortality of severe combined immunodeficiency, NKT cell-deficient, and CD1-deficient mice, indicating a major contribution of NKT cells to the Shwartzman reaction elicited by low doses of LPS, whereas at higher doses of LPS NK cells play a prominent role. These results suggest that the numerically small NKT cell population of normal mice apparently plays a mandatory role in the priming stage of the generalized Shwartzman reaction.

Immune response to Plasmodium vivax has a potential to reduce malaria severity.

Plasmodium falciparum infection causes transient immunosuppression during the parasitaemic stage. However, the immune response during simultaneous infections with both P. vivax and P. falciparum has been investigated rarely. In particular, it is not clear whether the host's immune response to malaria will be different when infected with a single or mixed malaria species. Phenotypes of T cells from mixed P. vivax-P. falciparum (PV-PF) infection were characterized by flow cytometry, and anti-malarial antibodies in the plasma were determined by an enzyme-linked immunosorbent assay. We found the percentage of CD3+delta2+-T cell receptor (TCR) T cells in the acute-mixed PV-PF infection and single P. vivax infection three times higher than in the single P. falciparum infection. This implied that P. vivax might lead to the host immune response to the production of effector T killer cells. During the parasitaemic stage, the mixed PV-PF infection had the highest number of plasma antibodies against both P. vivax and P. falciparum. Interestingly, plasma from the group of single P. vivax or P. falciparum malaria infections had both anti-P. vivax and anti-P. falciparum antibodies. In addition, antigenic cross-reactivity of P. vivax or P. falciparum resulting in antibodies against both malaria species was shown in the supernatant of lymphocyte cultures cross-stimulated with either antigen of P. vivax or P. falciparum. The role of delta2 +/- TCR T cells and the antibodies against both species during acute mixed malaria infection could have an impact on the immunity to malaria infection.

An alkaloid extract of Evanta, traditionally used as anti-Leishmania agent in Bolivia, inhibits cellular proliferation and interferon-gamma production in polyclonally activated cells.

Traditional medicine and scientific studies have shown that the raw extract of Evanta [Galipea longiflora, Angostura longiflora (Krause) Kallunki] exhibits anti-leishmanial activity. We hypothesized that the healing observed when using this plant might not only be due to the direct action on the parasite, but possibly to a parallel effect on the host immune response to the parasite involved in the healing process. We show here that an alkaloid extract of Evanta (AEE) directly killed the parasite already at a dose of 10 microg/ml, but at this low concentration, AEE did not have a major effect on viability and proliferation of eukaryotic cells. The whole extract was also found to be stronger than 2-phenylquinoline, the most prominent alkaloid in AEE. AEE was not directly stimulating B or T cells or J774 macrophages. However, it interfered with the activation of both mouse and human T cells, as revealed by a reduction of in vitro cellular proliferation and interferon-gamma (IFN-gamma) production. The effect was more evident when the cells were pretreated with AEE and subsequently stimulated with the polyclonal T-cell activators Concanavalin A and anti-CD3. Taken together, our results suggest that Evanta have a direct leishmanicidal effect and due to the effect on IFN-gamma production it might contribute to control the chronic inflammatory reaction that characterize Leishmania infection pathology, but in vivo studies are necessary to corroborate this finding.

Human monoclonal antibodies to Pf 155, a major antigen of malaria parasite Plasmodium falciparum.

Pf 155, a protein of the human malaria parasite Plasmodium falciparum, is strongly immunogenic in humans and is believed to be a prime candidate for the preparation of a vaccine. Human monoclonal antibodies to Pf 155 were obtained by cloning B cells that had been prepared from an immune donor and transformed with Epstein-Barr virus. When examined by indirect immunofluorescence, these antibodies stained the surface of infected erythrocytes, free merozoites, segmented schizonts, and gametocytes. They bound to a major polypeptide with a relative molecular weight of 155K and to two minor ones (135K and 120K), all having high affinity for human glycophorin. The antibodies strongly inhibited merozoite reinvasion in vitro, suggesting that they might be appropriate reagents for therapeutic administration in vivo.

Analysis of IL-4 promoter and VNTR polymorphisms in Thai patients with pulmonary tuberculosis.

Tuberculosis (TB) is a leading cause of morbidity and mortality in Thailand. Cytokines play important roles in defense against Mycobacterium tuberculosis infection. Interleukin (IL)-4 is one of the anti-inflammatory cytokines and has been found to be elevated in TB patients. The common polymorphisms in IL-4 gene, including IL-4-590C/T, IL-4-33C/T, and IL-4-variable number of tandem repeats (VNTR) intron 3 have been reported to be associated with risk for some diseases. The purpose of this study was to investigate possible associations between the above mentioned three common functional polymorphisms in the IL-4 gene in patients with pulmonary tuberculosis (PTB) in a Thai population. Forty three patients with PTB and 90 healthy control subjects were studied. The three common polymorphisms of the IL-4 gene were determined using polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP). The allele and genotype frequencies of IL-4 -590 C/T, -33 C/T, VNTR intron 3 polymorphisms did not show significant differences between PTB patients and healthy controls (genotype: p=0.88, p=0.92, p=0.40; allele: p=0.38, p=0.44, p=0.53, respectively). However, the allele distribution of the IL-4 -590 C, -33 C, and VNTR R3 was higher among PTB patients (25.58%, 25.58%, 25.58%, respectively) than among control subjects (20%, 20.48%, 19.44%, respectively). This may suggest that IL-4-590C/T, -33C/T and VNTR intron 3 might play a role in susceptibility to PTB. A larger cohort may possibly help conclude our findings.

Spleen enlargement and genetic diversity of Plasmodium falciparum infection in two ethnic groups with different malaria susceptibility in Mali, West Africa.

The high resistance to malaria in the nomadic Fulani population needs further understanding. The ability to cope with multiclonal Plasmodium falciparum infections was assessed in a cross-sectional survey in the Fulani and the Dogon, their sympatric ethnic group in Mali. The Fulani had lower parasite prevalence and densities and more prominent spleen enlargement. Spleen rates in children aged 2-9 years were 75% in the Fulani and 44% in the Dogon (P<0.001). There was no difference in number of P. falciparum genotypes, defined by merozoite surface protein 2 polymorphism, with mean values of 2.25 and 2.11 (P=0.503) in the Dogon and Fulani, respectively. Spleen rate increased with parasite prevalence, density and number of co-infecting clones in asymptomatic Dogon. Moreover, splenomegaly was increased in individuals with clinical malaria in the Dogon, odds ratio 3.67 (95% CI 1.65-8.15, P=0.003), but not found in the Fulani, 1.36 (95% CI 0.53-3.48, P=0.633). The more susceptible Dogon population thus appear to respond with pronounced spleen enlargement to asymptomatic multiclonal infections and acute disease whereas the Fulani have generally enlarged spleens already functional for protection. The results emphasize the importance of spleen function in protective immunity to the polymorphic malaria parasite.

Analysis of T-cell responses in malaria-exposed and non-exposed donors using Plasmodium falciparum asexual blood stages enriched by a simple centrifugation method.

Several studies have reported on similar in vitro cellular responses to different malaria-antigen preparations in both malaria-primed and un-primed donors. Whether intact live parasites can exert a distinct type of response in either of the two groups is not well known. In this study, we developed a simple three-step centrifugation method for simultaneous enrichment of early and late blood stages from Plasmodium falciparum cultures. Such enriched P. falciparum fractions and other antigen preparations were used to stimulate lymphocytes from malaria-exposed and non-exposed individuals to examine the proliferative activity and expansion of CD3+, gammadelta+, CD4+, and CD8+ T cells. While lymphocytes from malaria non-exposed donors proliferated relatively higher than those from malaria-exposed donors in response to most antigens tested, the enriched fractions of live parasites exerted higher proliferative responses on cells from the latter donors. This suggests the existence of memory cells in the malaria-exposed donors, but not in the non-exposed ones. Flow cytometric analysis revealed a higher percentage expansion of CD4+ T cells in the responding cells of the exposed donors than the non-exposed ones. Taken together, this study reports on a simple method that simultaneously enriches for intact live early and late blood stages of P. falciparum parasites. Moreover, the study revealed higher expansion CD4+ T cells in the exposed individuals than the non-exposed in response to live malaria parasites and not to other parasite-antigen preparations.

T-cell control of immunity to the asexual blood stages of the malaria parasite.

Both antibody-dependent and antibody-independent mechanisms are involved in immune protection against the asexual blood stages of the malaria parasite. It is well established that T cells play a crucial role in both induction and maintenance of this immunity. Of the two T-cell subsets (CD4+, CD8+) carrying alpha/beta T-cell receptors, the CD4+ T cells are of major importance for the development of blood stage immunity in both experimental and human malaria. In mice, CD4+ T cells comprise at least two functionally distinct cell types (TH1, TH2), distinguished on the basis of their lymphokine production. The balance between these subsets is critical for the outcome of an infection. In some rodent malarias, TH1 cells producing IFN-gamma and IL-2 are important for controlling infection in its early phases, while TH2 cells, producing i.a. IL-4 and IL-10, together with antibodies, are important for parasite clearance in later phases of infection. Distinct CD4+ T cells of either TH1 or TH2 type also have regulatory functions in human P. falciparum infection. In contrast to the CD4+ T cells, the role of CD8+ T cells in blood stage infection appears to be limited, but suppression of some CD4+ activities has been reported for both experimental and human malaria. As in other infections, peripheral T cells equipped with gamma/delta receptors are strongly upregulated in malaria and also respond to parasite antigens in vitro by proliferation and lymphokine production. However, the importance of the gamma/delta T cells for protection when compared with pathogenesis is presently unclear. Rapid advances made in recent years in the characterization and cloning of plasmodial antigens eliciting immune protection have made it possible to define some of the antigenic structures involved in T-cell immunity. This, together with an improved understanding of cellular mechanisms, provides some basis for the development of modern malaria vaccines.

Clinical pattern of severe Plasmodium falciparum malaria in Sudan in an area characterized by seasonal and unstable malaria transmission.

A hospital-based study was carried out in Gedarif town, eastern Sudan, an area of markedly unstable malaria transmission. Among the 2488 diagnosed malaria patients, 4.4% fulfilled the WHO criteria for severe malaria, and seven died of cerebral malaria. The predominant complication was severe malarial anemia (45.4%), followed by convulsions (21%), cerebral malaria (16. 4%) and hypotension (11.8%). Severe malaria was recognized in all age groups, but 44.5% of patients were aged 2 to 4 years. The mean ages of patients with severe anemia (5.6 years) and convulsions (5.9 years) were significantly lower than the mean ages of patients with cerebral malaria (14.1 years) or hypotension (35.2 years). Patients with convulsions and cerebral malaria had significantly higher mean parasite count (69972 and 56110 parasites/microL, respectively) than patients with severe anemia (24637 parasites/microL) or hypotension (13667 parasites/microL). The mean blood glucose level was higher in patients with cerebral malaria than in patients with anemia, and higher in patients who died than in patients who survived. In this setting, the clinico-epidemiological pattern of severe malaria varies considerably from that of hyperendemic regions in sub-Saharan Africa, and there is considerable variation between the individual complications of severe malaria.

Biology of gammadelta T cells in tuberculosis and malaria.

Tuberculosis and malaria remain the leading causes of mortality among human infectious diseases in the world. It is estimated that 3 to 5 million people die from tuberculosis and malaria each year. Although it is traditionally believed that CD4 and CD8 alphabeta T lymphocytes are mandatory for protective immune responses against Mycobacterium tuberculosis and Plasmodium falciparum (the ethiologic agents of tuberculosis and the most severe form of malaria, respectively), there is still incomplete understanding of the mechanisms of immune protection and of the causes of its failure in the affected patients. Several studies in humans and animal models have suggested that Vgamma9/Vdelta2 T cells may play an important role in the immune responses against Mycobacterium tuberculosis and Plasmodium falciparum. Vgamma9/Vdelta2 T cells represent about 75% of all circulating gammadelta T cells while they can be greatly expanded during the acute phase of Mycobacterium tuberculosis and Plasmodium falciparum malaria. Vgamma9/Vdelta2 T recognize a new class of antigenic molecules which are nonpeptidic in nature and contain critical phosphate moieties (phosphoantigens). Interestingly, phosphoantigens isolated from Mycobacterium tuberculosis and Plasmodium falciparum share strong structural homology and are probably identical. However, despite a large body of data reported in the literature, it is not yet clear whether Vgamma9/Vdelta2 T cells play a protective or pathogenic role in immune responses against Mycobacterium tuberculosis and Plasmodium falciparum. In this review we summarize our current knowledge of the biology of Vgamma9/Vdelta2 T cells in response to the two pathogens, Mycobacterium tuberculosis and Plasmodium falciparum, and provide evidence suggesting definition of a novel and important protective role through which Vgamma9/Vdelta2 T cells can contribute to the killing of microorganisms residing in intracellular compartments.

Interleukin-1 in adrenal chromaffin cells.

Interleukin-1, first identified as a macrophage factor of importance in infections and inflammation, is a protein with properties of an endogenous pyrogene and lymphocyte activating factor. Occurrence of interleukin-1-like immunoreactivity was demonstrated in the noradrenergic chromaffin cells of the rat and mouse adrenal gland by means of two antisera raised against synthetic peptides corresponding to the amino acid sequences 169-194 and 201-215 of the murine interleukin-1 precursor protein. These antisera also inhibited stimulation of interleukin-2 receptor expression by purified human interleukin-1. Reserpine, which is known to deplete catecholamines, also caused release of the interleukin-1-like immunoreactive material. The interleukin-1 content of the rat adrenal medulla was estimated by radioimmunoassay, and if released the adrenal interleukin-1 pool may result in plasma interleukin-1 levels of about 10(-12). The interleukin-1-immunoreactive material obtained from the rat adrenal gland was characterized as a trypsin-sensitive protein with a molecular weight in the range of 13,000-19,000. This protein fraction stimulated interleukin-2 receptor expression on human T-cells as earlier shown for interleukin-1.

Human T-cell responses to blood stage antigens in Plasmodium falciparum malaria.

Immunity to malaria involves both cell-mediated and humoral immune mechanisms. T cells are essential both in regulating antibody formation and in inducing antibody-independent immunity. Thus, acquisition and maintenance of protective immunity to malaria is T-cell dependent. Although relatively neglected until recently basic knowledge of T-cell subsets and cytokine production determining the course of a malaria infection is advancing rapidly at present. In this paper we will review recent findings contributing to the understanding of immune mechanisms against the asexual blood stages of human P. falciparum malaria.