gp120 binding and susceptibility to gp120-apoptosis in Th1 and Th2 clones. (A) gp120 binding to Th1 and Th2 clones. gp120 binding was analyzed by indirect immunofluorescence on cells (clone 3/12, Th1 and F37, Th2) sequentially incubated with the indicated doses of gp120, equal amounts of anti-gp120 MoAb, and fluorescein-conjugated goat antimouse (for fluorescence staining see Materials and Methods). Negative controls were cells incubated with fluorescein-conjugated goat antimouse only. (B) Differential susceptibility of Th1 and Th2 clones to gp120-apoptosis. Th1 clone 3/12 and Th2 clone F37 were treated with the indicated doses of gp120, and equal concentration of anti-gp120 MoAb; after 4 hours incubation of the cells in the presence of immobilized anti-TCR MoAb, the percentage of apoptotic cells was determined by TUNEL. Data are expressed as net % gp120-apoptosis (see Materials and Methods).