Both T and B Cells differentiate into Memory Cells, which remain in our lymph nodes and wait until we are re-exposed to the same pathogen.
When the Memory B cell is activated by the old antigen it makes large quantities on antibody quickly and kills the pathogen before it can infect us properly. The memory cells provide active immunity.
When we are exposed to a new antigen it takes us about a week to be able to make new antibody. However, a second exposure to antigen produces a much faster response, and several orders of magnitude higher levels of antibody are produced.
Plasma B cells make lots of antibody on re- exposure
Without immunity the level of antibody produced by plasma cells is much less
Passive Immunity is immunity to a pathogen without Memory cells. It can occur through antibody injection or from drinking breast milk (breast milk contains high [antibody])
Active Natural Immunity – the process above
Passive Natural Immunity – beastfeeding (antibody in milk)
Artificial Active Immunity – vaccination
Artificial Passive Immunity – antibody injection