B cells and T cells differ in their activation via antigen reception. B cells produce and release copies of the antibody they display on their surface. These antibodies flow through the body, looking to attach to an antigen in circulation.
T cells do not distribute antibodies. Instead, they set out on patrol, using their surface antigen receptors as eyes, looking for an invader.
B battle bacteria found in body fluids, while T vex viral infection, as well as other pathogens that take up resi-dence inside of host cells, using the machinery within to reproduce.
T tackle intracellular parasites, which fall into 2 cate-gories: facultative and obligate.
Facultative pathogens are versatile: they can replicate on their own but prefer the intracellular life because of the protection it affords. Macrophages are a popular home site. Facultative pathogens include Mycobacteria, which causes tuberculosis, and Leishmania, a protozoan parasite carried by sandflies, which bite and infect humans, caus-ing skin sores and other maladies.
Obligate intracellular pathogens must employ host cells to replicate. Viruses are obligate parasites.