Convert unknown KeyValuePair object to KeyValuePair<object, object>

Question

I have an object that is of type KeyValuePair<T1,T2> , but the actual types of T1,T2 are only known at run time. I would like to extract Key and Value of that object but I do not know how. Could you please help? (The idea is as below but it does not work)

public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer) {
     KeyValuePair<object, object> kvp = (KeyValuePair<object, object>)obj;
     Console.WriteLine("[{0},{1}]", kvp.Key, kvp.Value);
}