The immune response to malaria: regulation and protective immunity

Malaria is caused by infection with the protozoan parasite Plasmodium is responsible for more than 1 million deaths annually, mostly in young children. There is an urgent need to develop new intervention therapies. This project is aimed at understanding the immune response to the parasite, so that we will be able to design effective vaccine strategies and possibly immuno-therapy for treating the disease. An experimental model infection in mice is being used to determine the various ways the immune system can recognise and attack the parasite, which resides in red blood cells. In addition we are identifying the molecules of the parasite that are important for stimulating an effective immune response. When this is known, these molecules can be incorporated into a vaccine. Different way of administering vaccines are being tested in the mouse model. It is hoped that these studies can be directly applied to the human infection.

Objectives: We study processes involved in induction, regulation and specificity of immune responses in malaria. This involves studies in mouse models, mainly Plasmodium chabaudi, and in humans, Plasmodium falciparum. 1) To determine the effects of erythrocytic stage parasites on antigen presentation. 2) To generate transgenic mice with T cell- and B cell receptors specific for Plasmodium chabaudi antigens to determine CD4+ T cell and B cell regulation in blood-stage infection. 3) To investigate immune responses induced by immunisation with malarial proteins (including those epitopes recognised by the TCR and BCR transgenic mice). 5) To establish whether immune responses in mouse models, after infection by the natural route, are comparable with those induced by direct blood challenge. 6) To determine phenotype of human malaria-specific CD4+ T cells from mild and severe malaria, and antibody responses during and after transmission seasons. Methodology: 1) Generation of transgenic and knock-out mice: cloning of TCR and BCR genes into vectors. Breeding and screening by PCR and FACS 2) Isolation and culture of dendritic cells. FACS analysis and in vitro assays to measure cytokines by QRT-PCR and ELISA 3) Analysis of immune responses: antibody isotype (ELISA), cell responses and lymphoid architecture by microscopy and FACS 4) Cloning of Plasmodium genes coding for malarial antigensinto expression vectors. 5) Measurement of human T cell responses; by FACs, ELISA, and QPCR. Clinical Research: The studies on human immune responses are carried out on PBMC from Europeans and volunteers from an endemic area of P.falciparum transmission (Kilfi, Kenya). T cell responses are measured to determine which responses correlate with severe malaria. We will determine whether antibody responses are short-lived and whether affinity maturation takes place. Summary: Animal models of blood stage malaria infection have shown that protective immunity depends on CD4 T cells and antibody. In order to extrapolate to human infections it is important to know that immune mechanisms in several models are similar, and that immunity following mosquito transmission is comparable to direct blood challenge. We study responses to different rodent parasites with and without mosquito transmission to determine how far P. chabaudi infections represent other rodent infections.The first APC in the body that activate T cells are likely to be dendritic cells (DC). Investigations with DC, parasites and T cells will allow the determination of parasite interference with antigen presentation. Using genetically manipulated mice, it is possible to follow specific responses in vivo: lifespan of immune cells, their interaction with DC and other APC, activation requirements and subsequent responses. We will relate our findings to immune responses in humans to P. falciparum. Implications for improving health or health care: Malaria is a major cause of mortality and morbidity. The problems of drug resistance make other methods of control imperative. Our work will further the understanding immune responses in protection and immunopathology particularly protective mechanisms involved in response to antigens such as MSP1, a leading vaccine candidate. These studies will aid in the rational design of an effective malaria vaccine.