The hypothesis that T cell competition for access to APC influences priming of CTL responses is a controversial issue. A recent study using OVA as a model Ag supports this hypothesis and received considerable attention. However, using a comparable approach, we reached a different conclusion. We analyzed whether TCR transgenic T cells specific for lymphocytic choriomeningitis virus gp33-41/D(b) could inhibit the priming of endogenous responses against gp33-41 and against two other lymphocytic choriomeningitis virus glycoprotein-derived CTL epitopes. After priming with different stimuli, gp33-41/D(b)-specific TCR transgenic T cells reduced the endogenous gp33-41/D(b) response in a dose-dependent way, but all other endogenous responses were unaffected. Even when >10(6) TCR transgenic cells were combined with weak priming, no reduction of responses other than of those specific for gp33-41/D(b) was observed. Thus, competition for APC by CTLs of different specificities is not of functional relevance in antiviral immune responses.