DEFICIENT PEPTIDE LOADING AND MHC CLASS-II ENDOSOMAL SORTING IN A HUMAN GENETIC IMMUNODEFICIENCY DISEASE - THE CHEDIAK-HIGASHI-SYNDROME

The Chediak-Higashi syndrome (CHS) is a human recessive autosomal dise ase caused by mutations in a single gene encoding a protein of unknown function, called lysosomal-trafficking regulator. All cells in CHS pa tients bear enlarged lysosomes, In addition, T- and natural killer cel l cytotoxicity is defective in these patients, causing severe immunode ficiencies, We have analyzed major histocompatibility complex class II functions and intracellular transport in Epstein Barr Virus-transform ed B cells from CHS patients. Peptide loading onto major histocompatib ility complex class II molecules and antigen presentation are strongly delayed these cells, A detailed electron microscopy analy sis of endo cytic compartments revealed that only lysosomal multilaminar compartme nts are enlarged (reaching 1-2 mu m), whereas late multivesicular endo somes have normal size and morphology, In contrast to giant multilamin ar compartments that bear most of the usual lysosomal markers in these cells (HLA-DR, HLA-DM, Lamp-1, CD63, etc.), multivesicular late endos omes displayed reduced levels of all these molecules, suggesting a def ect in transport from the trans-Golgi network and/or early endosomes i nto late multivesicular endosomes, Further insight into a possible mec hanism of this transport defect came from immunolocalizing the lysosom al trafficking regulator protein, as antibodies directed to a peptide from its COOH terminal domain decorated punctated structures partially aligned along microtubules, These results suggest that the product of the Lyst gene is required for sorting endosomal resident proteins int o late multivesicular endosomes by a mechanism involving microtubules.