title: Cellular location of thymus-leukemia (TL) antigen as shown by immuno-cryoultramicrotomy.
abstract: Thymus-leukemia (TL) antigen is a class I molecule of the major histocompatibility complex that is expressed on the surface of mouse cortical thymocytes. Though not expected, it has been reported that TL antigen can be found on isolated mitochondria of TL+ cells. We used immuno-cryoultramicrotomy to look for TL on mitochondria in situ, thereby avoiding the plasma membrane contamination that occurs when isolating organelles. Establishing optimal fixation conditions was crucial, as mitochondrial structure was not preserved by the low concentrations of fixative needed for detection of antibody labeling. The plasma membranes of tissue culture and thymus cells were labeled well with anti-TL antibody and protein A-gold conjugate, while mitochondria within the cells were not labeled. Isolation of mitochondria on a one-step Ficoll gradient resulted in a purer organelle preparation than did isolation of mitochondria by centrifugation alone. Generally, mitchondria within this purer preparation were not labeled. Our data show that under conditions where contamination by plasma membrane is not a major concern, TL antigen cannot be detected on mitochondria.
authors.affiliation: Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9050.
authors.forename: C
authors.initials: C
authors.lastname: Hartfield
authors.forename: A
authors.initials: A
authors.lastname: McDowall
authors.forename: B
authors.initials: B
authors.lastname: Loveland
authors.forename: K
authors.initials: K
authors.lastname: Fischer Lindahl
mesh_terms: D000818:Animals; D000906:Antibodies; D000951:Antigens, Neoplasm / Q000032:analysis*; D002458:Cell Fractionation / Q000379:methods; D006046:Gold; D008562:Membrane Glycoproteins / Q000032:analysis*; D016253:Microscopy, Immunoelectron / Q000379:methods*; D008928:Mitochondria / Q000276:immunology*; D013205:Staphylococcal Protein A; D014407:Tumor Cells, Cultured
chemical_list: D000906:Antibodies; D000951:Antigens, Neoplasm; D008562:Membrane Glycoproteins; D013205:Staphylococcal Protein A; C028388:thymus-leukemia antigens; D006046:Gold