Expression of idiotype 315 (Id315) and I-A antigens in MOPC-315 tumor cells grown in vivo

MOPC-315 murine myeloma grown intraperitoneally as ascites cells in BALB/cJ mice were removed at successive days after transplantation. They were stained for Id³¹⁵ and I-A markers by indirect immunofluorescence techniques by means of FITC conjugates. Flow cytometry (FCM) measurements on cell surface markers were correlated with the phase of the cell cycle by quantitating cellular DNA of cells stained with propidium iodide. Variations in cell size due to cell growth were determined by low-angle light scattering. FCM data on the two cell surface markers were normalized for unit cell surface and cell volume. Cells grew rapidly in the early days (5–7) of tumor growth. No significant variation in the expression of surface markers was observed during this period. Parallel with a slowdown in cell growth, the expression of Id³¹⁵ increased about threefold between the 7th and 9th days. The increase in the Id³¹⁵ marker was dependent on the cell cycle, with G₁ cells having the highest density. No cell cycle dependence was observed for the I-A marker.