FIG. 3.

Ribosyltransferase activity of the A subunit is necessary for inhibition of antigen processing, whereas antigen presentation is enhanced by toxin preparations that lack A subunit enzymatic activity. Macrophages were treated overnight with or without the toxin preparations (1 μg/ml), washed, incubated with viable HB101.Crl-HEL for 2 h at 37°C, and fixed. Antigen presentation was determined by incubation with 3A9 T hybridoma cells for 20 to 24 h at 37°C.