Recent work shows that, in an open loosely coupled MAS, it is difficult to deal with semantic heterogeneity between agents in a static way. In this paper, we present an interaction protocol for the request interpretation which permits to manage the semantic heterogeneity when the ontology alignment is incomplete. We first briefly describe the messages translation mechanism, based upon the presence of an ontology alignment service. We then present the answer strategy of our agents, which relies on several specific performatives. We propose an experimental evaluation.