Resistance to intranasal infection with Balamuthia mandrillaris amebae is T-cell dependent

T and B cell-deficient BALB/c SCID mice become severely ill and die of amebic encephalitis after intranasal infection with Balamuthia mandrillaris, while adult immunocompetent BALB/c wild-type (WT) mice are resistant. To further investigate the role of lymphocytes in protection from Balamuthia amebic encephalitis (BAE), SCID mice were reconstituted with and WT mice selectively depleted of lymphocytes before infection. Reconstitution of SCID mice with whole spleen cells from WT mice rendered the recipients as resistant to BAE as WT mice. SCID mice that had received spleen cells depleted of CD4(+) T cells remained susceptible. When adult WT mice were depleted of both CD4(+) and CD8(+) T cells or of CD4(+) T cells alone, these mice also became susceptible to BAE. Depletion of CD8(+) T cells alone increased susceptibility only marginally. All morbidity and mortality data were underpinned by histological analysis of the brain.