Defective granule exocytosis in Rab27a-deficient lymphocytes from Ashen mice.
Because mutations in Rab27a have been linked to immune defects in humans, we have examined cytotoxic lymphocyte function in ashen mice, which contain a splicing mutation in Rab27a. Ashen cytotoxic T lymphocytes (CTLs) showed a >90% reduction in lytic activity on Fas-negative target cells compared with control C3H CTLs, and ashen natural killer cell activity was likewise diminished. Although their granule-mediated cytotoxicity pathway is profoundly defective, ashen CTLs displayed a normal FasL-Fas cytotoxicity pathway. The CD4/8 phenotype of ashen T cells and their proliferative responses were similar to controls. Ashen CTLs had normal levels of perforin and granzymes A and B and normal-appearing perforin-positive granules, which polarized upon interaction of the CTLs with anti-CD3-coated beads. However, rapid anti-CD3-induced granule secretion was drastically defective in both CD8(+) and CD4(+) T cells from ashen mice. This defect in exocytosis was not observed in the constitutive pathway, as T cell receptor-stimulated interferon-gamma secretion was normal. Based on these results and our demonstration that Rab27a colocalizes with granzyme B-positive granules and is undetectable in ashen CTLs, we conclude that Rab27a is required for a late step in granule exocytosis, compatible with current models of Rab protein function in vesicle docking and fusion.
Experimental Immunology Branch, National Cancer Institute;, and.
E K
EK
Haddad
X
X
Wu
J A
JA
Hammer
P A
PA
Henkart
D000069594:Abatacept; D000818:Animals; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism; D060908:CTLA-4 Antigen; D003602:Cytotoxicity, Immunologic; D005089:Exocytosis; D018796:Immunoconjugates; D007371:Interferon-gamma / Q000378:metabolism; D007694:Killer Cells, Natural / Q000378:metabolism*; D051379:Mice; D008817:Mice, Mutant Strains; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D013154:Spleen / Q000166:cytology; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
D015703:Antigens, CD; D000943:Antigens, Differentiation; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; C556707:Ctla4 protein, mouse; D018796:Immunoconjugates; D011948:Receptors, Antigen, T-Cell; D000075745:rab27 GTP-Binding Proteins; D000069594:Abatacept; D007371:Interferon-gamma; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins