Integrin α_Dβ₂ influences cerebral edema, leukocyte accumulation and neurologic outcomes in experimental severe malaria

Malaria is an infectious disease of major worldwide clinical importance that causes a variety of severe, or complicated, syndromes including cerebral malaria, which is often fatal. Leukocyte integrins are essential for host defense but also mediate physiologic responses of the innate and adaptive immune systems. We previously showed that targeted deletion of the α_D subunit (α_D ^-/-) of the α_Dβ₂ integrin, which is expressed on key leukocyte subsets in mice and humans, leads to absent expression of the integrin heterodimer on murine macrophages and reduces mortality in mice infected with Plasmodium berghei ANKA (P. berghei ANKA). To further identify mechanisms involved in the protective effect of α_D deletion in this model of severe malaria we examined wild type C57BL/6 (WT) and α_D ^-/- mice after P. berghei ANKA infection and found that vessel plugging and leukocyte infiltration were significantly decreased in the brains of α_D ^-/- animals. Intravital microscopy demonstrated decreased rolling and adhesion of leukocytes in cerebral vessels of α_D ^-/- mice. Flow cytometry analysis showed decreased T-lymphocyte accumulation in the brains of infected α_D ^-/- animals. Evans blue dye exclusion assays demonstrated significantly less dye extravasation in the brains of α_D ^-/- mice, indicating preserved blood-brain barrier integrity. WT mice that were salvaged from P. berghei ANKA infection by treatment with chloroquine had impaired aversive memory, which was not observed in α_D ^-/- mice. We conclude that deletion of integrin α_Dβ₂ alters the natural course of experimental severe malaria, demonstrating previously unrecognized activities of a key leukocyte integrin in immune-inflammatory responses that mediate cerebral involvement.