Early Indus Valley Civilization ... their Geograhpy, their customs and Indo-Aryan civilization with the earliest caste system.
Antibodies contribute to immunity in three main ways: they can prevent pathogens from entering or damaging cells by binding to them; they can stimulate removal of a pathogen by macrophages and other cells by coating the pathogen; and they can trigger direct pathogen destruction by stimulating other immune responses such as the complement pathway.
The antibodies act sort of like flag markers. They stick to the antigens and tell the immune system what type of antigen it is on so that it can destroy it. Each antibody is made for each antigen. For instance a specific antibody is created to help destroy the chickenpox virus.