In this study, monocyte-derived IL-12 was the trigger for NK-cell activation, and it also augmented the IFN-γ response. While Obeticholic Acid the ensuing proinflammatory response was associated with better parasite control, it was at the expense of the development of clinical symptoms. Together, these findings

underline the dual role of TNF in protection and pathology and the importance of a regulated TNF/IL-10 balance in the prevention of severe disease. These human studies were confirmed by experimental studies in mice with the parasites P. yoelii 17XL, P. yoelii 17XNL [72, 73] and P. chabaudi [74]. Depending on specificity and subclass, antibody can protect the host against blood-stage parasites by neutralization, opsonizing complement-mediated lysis or phagocytosis, BGB324 or by blockade of receptor-mediated merozoite invasion of red blood cells [75]. In mice vaccinated against the lethal P. yoelii 17XL parasite by either subcutaneous or intraperitoneal injection of MSP1 plus adjuvant, protection correlated with the presence of opsonizing antibodies of classes IgG1, IgG2a and

IgG2b at the time of parasite clearance [24, 27]. Mouse complement fixing immunoglobulins IgG1, IgG2a and IgG2b exhibit strong binding to FcγRII receptors [76]. However, antibody alone was not sufficient for complete parasite elimination. The most protective vaccines, including purified MSP-1 [77], also induced strong DTH-type T-cell responses to Acyl CoA dehydrogenase lethal P. yoelii 17XL antigens, and recent studies of immunization with recombinant P. falciparum MSP-2 antigen in a mouse model suggest that skewing towards the IgG2b subclass is driven by defined T-cell epitopes [17]. Antibody class switching appears to be influenced by the cytokine environment during the early immune response or by epitope-specific T cells, as suggested by these experiments in mice [17]. The antibody response to relevant conserved antigens depends on the initial T-cell recognition of processed antigen presented in association with MHC molecules.

As well as the strong T-cell activation observed in mice vaccinated against the lethal P. yoelii17XL, there was a significant increase in the homing of bone marrow cells to the spleen and liver at the time of recovery [78, 79]. Moreover, peripheral blood, bone marrow and spleen cells from recovered mice were more effective at killing parasites than controls, both in vitro and in passive transfer experiments in vivo, effects that were enhanced by antibody. We suggested that T-cell-mediated immunity might contribute to recovery by enhancing cell migration, by activating the cells or by ‘arming’ them. Vaccination caused parasites, effector cells and antibody to collect in the liver, a plausible site for their interaction [79].