Temporary Disappearance (“eclipse”) of LPC-1 Plasmacytoma M Component Synthesis Following Tumor Cell Transfer

The early phase of LPC-1 plasmacytoma development was studied by in vivo labeling with [6-¹⁴C]arginine using its M component (immunoglobulin G 2a, k) as marker. At a time when M component was not detected or faint by protein staining of electrophoretograms, significant labeling of M component was detectable by autoradiography. Labeling of the M component was fairly constant for the first 10 hr but was markedly decreased from Days 1 to 7. Nadir (0 to 3% of initial 30-min value) was observed on Day 3. Recovery of M component labeling to the 30-min level was complete by Day 13. This period of marked reduction or “eclipse” in newly synthesized M component was shortened by 2 days when mice were pretreated with pristane or cyclophosphamide prior to tumor cell transfer. The eclipse period was also 2 days shorter in athymic BALB/c-nu/nu mice than in normal BALB/c mice. The eclipse period corresponds to the classical “lag” following tumor cell transfer before tumor growth can be detected by conventional methods. The sensitivity of the [6-¹⁴C]arginine pulse permits the in vivo detection of small numbers of tumor cells (as few as 10⁶ cells) over the early time periods after cell transfer. Modification of eclipse by manipulating host and/or tumor cells may elucidate the accompanying cellular and biochemical events.