In twelfth-century China, people seeking protection from smallpox removed scabs from people mildly scarred from the disease - HSC - SSCE Biology - Question 23 - 2001 - Paper 1

The practices of removing scabs from mildly scarred individuals and exposing healthy individuals to them can be explained through the understanding of the immune response.

Firstly, upon inhalation or injection, the smallpox antigens present in the scabs would stimulate the immune system of the healthy individuals. This leads to the activation of B and T cells, which are crucial for adaptive immunity.

Secondly, specifically, B cells would recognize the smallpox antigens and begin producing antibodies. These antibodies bind to the virus and neutralize it, preventing infection. In addition, T cells would target and destroy any infected cells, contributing to the immune defense.

Furthermore, the exposure acts as a form of vaccination, allowing the immune system to develop memory cells. These memory cells ensure a faster and stronger response if the individual encounters the actual smallpox virus in the future, thereby providing immunity against the disease.

In summary, the success of these practices relied on the stimulation of the adaptive immune response, including the production of antibodies and the development of cell-mediated immunity.