The architecture you describe isn't normally how things are done, or at least not the typical terminology.
Normally, you have a PC that is an OPC server, which pulls data from the PLCs. The job of the OPC server is to get data, and make it available.
You also have OPC clients, who access the data in the OPC server. They could have read only access, or they may be able to read and write.
As an example, it is common for something like an HMI or SCADA system to talk to one OPC server, instead of managing connections directly to a number of PLCs. The OPC server handles the details of communicating to different PLC brands, and the SCADA system just needs to be an OPC client.