Question

In his History of the Peloponnesian War, the Greek historian Thucydides wrote that during the Plague of Athens in 430 BCE, individuals who survived the plague were able to care for the sick without risk because they were immune as a result of their recovery. This is the first recorded observation of immunity to infectious disease, but it is only in modern times that we have the tools to understand the source of that immunity.

EXPLAIN HOW the immune system protects the body from re-infection after it has cleared a pathogen. Which cell types are involved? How are those cells made, and what is special about them? What happens during the initial encounter with the pathogen? How do these events lead to protection at a later time? How is the protection maintained?

Please be as specific and detailed as you possibly could.

Answer 1

immunity

What happens during the initial encounter with the pathogen?

When the immune system first encounters a pathogen there are different reactions taking place:

Firstly neutrophiles arrive at the site of infection, these types of cells phagocyte and eliminate the pathogens at the same time they recruit other cell types like macrophages, another phagocytic cell whit the capability of engulfing much more pathogens that a neutrophile, both cells are members of the innate immune system, if their action is not enough to eliminate the threat, then another innate immune cell comes into action, the dendritic cell.

Dendritic cells are what is called professional antigen presenter cells, they phagocyte pathogens or fragments of pathogens, processing them and presenting the peptidic fragments in the membrane on the major histocompatibility complex, then the dendritic cell migrates to a lymph node, where they will interact whit T-cells activating them specifically against the threat by the means of the pathogenic fragments, this will lead to the formation of three T-cells populations cytotoxic t cells, helper T cells, and memory t cells.

Part of the helper T cells alongside the cytotoxic t cells will migrate to the site of infection, the other group of helpers will go to activate B cell which in turn will produce antibodies and memory B cells, and the memory T cells will stay in the lymph node.

Cytotoxic T cells, antibodies form B cells, helper T cells, and macrophages will resolve the infection.

How do these events lead to protection at a later time? How is the protection maintained?

The individual has now been protected against the resurgence of the same threat, thanks to the memory B cells and the memory T cells which now at the re-exposure of the same threat will quickly produce specific T cells and antibodies. This type of cell remains whit in the body for up to 20 years.