Acute P. falciparum malaria induces a loss of CD28- T IFN-gamma producing cells

Examining cellular immune responses to inform development of a blood-stage malaria vaccine

Naturally acquired immunity to the blood-stage of the malaria parasite develops slowly in areas of high endemicity, but is not sterilizing. It manifests as a reduction in parasite density and clinical symptoms. Immunity as a result of blood-stage vaccination has not yet been achieved in humans, although there are many animal models where vaccination has been successful. The development of a blood-stage vaccine has been complicated by a number of factors including limited knowledge of human-parasite interactions and which antigens and immune responses are critical for protection. Opinion is divided as to whether this vaccine should aim to accelerate the acquisition of responses acquired following natural exposure, or whether it should induce a different response. Animal and experimental human models suggest that cell-mediated immune responses can control parasite growth, but these responses can also contribute to significant immunopathology if unregulated. They are largely ignored in most blood-stage malaria vaccine development strategies. Here, we discuss key observations relating to cell-mediated immune responses in the context of experimental human systems and field studies involving naturally exposed individuals and how this may inform the development of a blood-stage malaria vaccine.

Neuronal apoptosis, metallothionein expression and proinflammatory responses during cerebral malaria in mice

BACKGROUND

Cerebral malaria (CM) is an acute encephalopathy in humans due to the infection with Plasmodium falciparum. Neuro-cognitive impairment following CM occurs in about 10% of the treated survivors, while the precise pathophysiological mechanism remains unknown. Metallothionein I + II (MT-I + II) are increased during CNS pathology and disorders. As previously shown, MT-I + II are neuroprotective through anti-inflammatory, antioxidant and antiapoptotic functions. We have analyzed neuronal apoptosis and MT-I + II expression in brains of mice with experimental CM.

METHODS

C57BL/6j mice, infected with Plasmodium berghei ANKA, were studied on day 7, day 9, and when presenting signs of CM on days 10-12. We investigated brain histopathology by immunohistochemistry and TUNEL (Terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-digoxigenin nick end labeling). For statistics, we used quantitation (cellular counts) of the analyzed variables.

RESULTS

During CM, we observed significant inflammatory responses of F4/80+ microglia/macrophages and GFAP+ reactive astrocytes and increased immunoreactivity of 8-oxoguanine (marker of oxidative stress). As novel findings, we show: (1) a localized CM-induced neuronal apoptosis (detected by TUNEL) indicating severe and irreversible pathology. (2) A significant increase in MT-I + II expression in reactive astrocytes, macrophages/microglia and vascular endothelium.

INTERPRETATION

This is the first report showing apoptosis of neurons in CM by TUNEL, pointing out a possible pathophysiological mechanism leading to persisting brain damage. The possible neuroprotective role of MT-I + II during CM deserves further attention.