My idea is that passive immunity can be used to cure an individual who is infected with a certain disease. For example, for someone infected by clostridium tetani, you would inject them with an antiserum. The antibodies give protection against bacteria, until the active immune response takes action. In this link (http://pmt.physicsandmathstutor.com/download/Biology/A-level/Notes/Edexcel-IAL/Unit-4/6-Infection-Immunity-and-Forensics/Set-A/Vaccines.pdf), page 3, the graph shows that the level of antibodies in the blood actually rises after injection! To me, this naturally begs the question, what is the mechanism by which passive immunity operates (because I want to know why the level of antibodies rise in order to understand the situation dynamically)?
[Note: would I be correct in saying that a short answer would be that the level of antibodies rises because the active immune system is stimulated due to the enhancement of phagocytosis by macrophages when the antibodies attach to the antigens? My book states that release of antibodies (by B-cells) that bind to the antigen is required to allow the macrophages to engulf the pathogen with the specific surface antigen.]