Defective Granule Exocytosis in Rab27a-Deficient Lymphocytes from Ashen Mice

EK Haddad, X Wu, JA Hammer III… - The Journal of cell …, 2001 - rupress.org
EK Haddad, X Wu, JA Hammer III, PA Henkart
The Journal of cell biology, 2001rupress.org
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 …
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-γ 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.
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