This study reports a labeled (5-carboxyfluorescein diacetate succinimidyl ester [CFSE]), adoptive transfer system to quantitate antigen specific (transgenic) CD4+ T-cell responses to recombinant peptide (Listeria monocytogenes [LM] expressing ovalbumin [OVA]). Proliferative responses to peptide were assessed by the following the decay of CFSE fluorescence in the OVA specific CD4+ cells by flow cytometry. CD4+ and CD8+ responses (in a similar, viral peptide based model) were demonstrated to be very different. In response to a similar stimulus, CD8+ T cells expanded at least 10-fold more than CD4+ T cells. This was assessed by both CFSE decay and population size at day 8. Additionally, a much smaller percentage of CD4+ cells differentiated to effector Interferon-? production (27% CD4+ versus >85% CD8+). This difference was noted even after prolonged exposure to antigen.
The effect of the specific peptide used in the study (LM), or the efficiency of its presentation by MHC I versus MHC II, on T-cell responses was tested and shown not to affect basic proliferative responses. Furthermore, the transgenic cells used and the viral vector for OVA peptide were varied without affecting the original findings. Stimulation with anti-CD3 in the presence of IL-2 with and without costimulation from anti-CD28 also resulted in proliferative responses similar to those of the described model.