His shirt was unbuttoned, his jacket discarded on the floor and, as I steered a wide berth around him, alarm bells started ringing in my head when he set his attention to unbuckling the belt of his trousers. Such a scene is not customary in the corridors of the Parasitology department of the University

of Heidelberg, not least at 9 am on a Monday morning, and to state that this spectacle caused quite a stir would be no understatement. Puzzled and perturbed, I nonetheless continued my walk to the lab, where I work on the Plasmodium parasite. I shall return to the topic of this gentleman because, although this tale doesn’t seem relevant for readers of an immunology journal, all will become clear later. The entire Parasitology department

in Heidelberg focuses on Plasmodium, and my particular interest is the immunology of this devious protist. Its complex and multifaceted life cycle starts with an infected mosquito see more (Figs. 1) taking a blood meal from an unfortunate mammal (Figs. 2), by which process parasites are deposited in the skin. A whistle-stop tour of the body then commences, as parasites travel from skin to blood, Erastin blood to liver, liver to bloodstream, with a quick pitstop at the lung before heading back to the bloodstream – only to be taken up by a mosquito again. The capacity of Plasmodium to metamorphose so dramatically and hijack so many components of the host organism has required the development of a neat box of tricks utilized to perplex the host immune response. Take, for example, antigenic variation. Infected erythrocytes adhere to host endothelial cells in the brain, liver, heart and

placenta. It is this sequestration, particularly in the brain microvasculature and placenta, which respectively leads to cerebral and pregnancy-associated malaria symptoms. Sixty var genes encode PfEMP1, (Plasmodium falciparum erythrocyte membrane protein 1) in ring stage parasitized erythrocytes, and PfEMP1 is known to bind CD36, ICAM-1 and other host receptors, mediating adhesion and promoting cerebral symptoms. The immune system diligently produces antibodies that inhibit binding of infected during erythrocytes and is capable of doing it quite well 1, but the parasite counters this by switching expression to another of its 60 var genes, and legions of new clones can surge forward uninhibited. Astoundingly, one of the var genes, var2csa, binds exclusively to the placenta and is only found in pregnant women, under the control of unique regulatory transcription mechanisms 2 capable of selective expression in pregnant hosts. One can only reluctantly admire the cunningness of this bug. The capacity for Plasmodium to confound the immune system also extends to T cells. Two classic proteins that have effectively become folklore in malaria circles are MSP-1 and CSP, the merozoite surface and circumsporozoite proteins, expressed in the blood and sporozoite stages respectively.