Support for human-to-human interactions over a network is still insufficient, particularly for professional virtual communities (PVC). Among other limitations, adaptation capabilities of humans are not taken into account in existing models for collaboration processes in PVC. This paper presents a model for adaptive human collaboration. A key element of this model is the modeling of some social elements involved during the collaboration process. Processes are modeled as social protocols. A second contribution is the proposition of negotiation as a mean for adaptation of these protocols.