Evaluation of T helper function in lines of mice selected for high or low antibody production: quantitative inhibition of immune responses by anti-L3T4+ monoclonal antibody.

The potentialities of T helper cell compartment were compared in lines of mice selected for high or low Ab production against heterologous erythrocytes (H1 and L1 mice) by investigating the "in vivo" and "in vitro" modulation of immune responses by GK 1-5 anti-L3T4+ mAb. FACS analysis showed a frequency of L3T4+ cells similar in non-immunized mice of both lines. However, LI mice were more susceptible to inhibition of the IgG Ab response to SE when injected GK 1-5 prior to immunization. The "in vitro" proliferation of T cells specific for HEL was higher in HI than in LI LN cultures, and a higher GK 1-5 mAb concentration had to be applied to HI cultures in order to produce the inhibitory effect. In contrast, during MLR, the capacity for T proliferation was similar in HI and LI cultures stimulated by a common F1 target. This allo-Ag-induced proliferation was inhibited at similar GK 1-5 mAb concentrations in the two lines. These results demonstrate that there is no intrinsic L3T4+ cell deficiency in LI mice. Differences in GK 1-5 mAb required for inhibition of responses to Ag (other than allo-Ag) in HI and LI mice are mainly due to different macrophage T cell triggering.