LOSS OF CYTOTOXIC T-LYMPHOCYTE FUNCTION IN CHEDIAK-HIGASHI-SYNDROME ARISES FROM A SECRETORY DEFECT THAT PREVENTS LYTIC GRANULE EXOCYTOSIS

CTLs from patients with Chediak-Higashi syndrome (CHS) are unable to d estroy target cells recognized via the TCR. To determine the mechanism responsible for the loss of cytotoxicity, CD8(+) CTL clones have been derived from a patient with CHS. Individual CTL clones show poor kill ing that can be increased in longer assays. However, in the presence o i cycloheximide, the small amount of killing observed is abolished, in dicating killing arises from newly synthesized proteins, rather than f rom proteins stored in granules. In this study, we show that the CHS C TL clones express normal levels of the lytic proteins granzyme A, gran zyme B, and perforin, which are processed properly during biosynthesis and targeted correctly to giant lytic granules. Despite the differenc e in size, CHS and normal lytic granules are similar, in that both con tain the lysosomal enzyme cathepsin D and the lytic protein granzyme A , and lack the mannose-6-phosphate receptor (MPR). However, unlike nor mal CTL clones, the CHS CTL clones are unable to secrete their giant g ranules in which the lytic proteins are stored. After cross-linking th e TCR, CHS CTL clones fail to secrete granzyme A, as assayed by both e nzyme release and confocal microscopy. We suggest that the defect in C HS lies in a protein that is involved in membrane fusion and is essent ial for the secretion of lysosomal compartments in certain hemopoietic cells.