Induction of rods and rings (RR) formation in COS-7 and HeLa cells with different inhibitors of the CTP/GTP biosynthetic pathway. (A-C) RR structures induced in COS-7 cells by 1 mM ribavirin and detected by the prototype human anti-RR serum (A) and rabbit anti-IMPDH2 antibody (B), with co-staining demonstrated in the merged image (C). (D-E) Induction of RR with DON (D) and MPA (E) in COS-7. (F) HeLa cells treated with 1 mM ribavirin. (G) In untreated COS-7 cells, no RR was observed. D, E, F, and G show merged images of human anti-RR serum and rabbit anti-IMPDH2 staining. Yellow color in all merged images (C-F) means labeling by both probes. Nuclei were counterstained with DAPI (blue) in all images (C-G). Bars: 20 μm. Arrows: rods; arrowheads: rings. (H-I) Quantitative analysis of RR induction. Different concentrations and time points of ribavirin showed 1 mM (1000 μM) and 2 h with >90% of RR in COS-7 cells. (I) DON and MPA showed in 2–4 h of treatment >50% of COS-7 with RR. (H-I) Experiment was repeated #one, ##two or ###three times and ~130-150 cells were counted for each experiment.