Structural differences between sensitive and resistant L1210 cells.

The main structural differences between sensitive L1210 mouse leukaemic cells and their multidrug resistant counterpart, obtained by adaptation of the parental cell line to vincristine (VCR), concern the size and shape of the cells, their surface properties and changes in organelles involved in proteosynthesis and transport of substances. The resistant cells are larger with higher density of microvilli. In light and electron micrographs containing a group of cells, cells were found to be closer to each other in L1210/VCR cells than in L1210 cells. This difference in cell aggregation suggests different surface properties which could be visualised by decreased staining of L1210/VCR cell surface coat (glycocalyx) with a polycationic dye ruthenium red. A decrease in surface to volume ratio as a consequence of increased cell size in resistant cells is compensated by proliferation of villi and cytoplasmic protrusions of the cell surface. L1210/VCR cells were further distinguished by higher amount of euchromatin, increase in density of rough endoplasmic reticulum, more developed Golgi apparatus and aggregation of free ribosomes into tetrameric and pentameric polyribosomes. These structural changes may be interpreted as a sign of increase in proteosynthesis and transport of substances.

Lymphomas with acquired mouse mammary tumor virus proviruses resemble distinct prethymic and intrathymic phenotypes defined in vivo.

A number of murine T cell lymphomas expressing the T cell Ag Thy-1 contain acquired mouse mammary tumor (MMTV) proviruses. These lymphomas all express detectable levels of MMTV RNA, yet the majority of the tumors fail to produce MMTV particles. To determine if the ability of lymphomas to produce MMTV is a reflection of the differentiation state of the tumor, we examined eight lymphomas for expression of surface B and T cell Ag as well as for rearrangements and expression of TCR genes. All tumors could be grouped into three categories observed in vivo, including early lymphoid, nonmature intrathymic T cells, and immature intrathymic T cells. Cell lines corresponding to all three phenotypes produced MMTV particles, suggesting that production of virus is not linked to the differentiation state of lymphoid cells. These studies highlight the potential advantage of studying T cell lymphomas vs mixed primary populations or T cell hybridomas for evaluation of both phenotypic and molecular markers in clonal T cells.