What exactly are these things?

Question

What exactly are the primary and secondary immune systems? I always thought there was just one immune system. What are their jobs? Do they deal with antigens the same way? What would the primary immune system do to an antigen? What would the secondary immune system do to the same antigen?

Yea I'm writing an essay on this stuff and I really have no idea what I'm doing, I need something that'll explain all this in layman's terms, I just made a list of all the questions I have and put them up there, if you can answer any of them, I'll be grateful.

Answer 1

There are basically three levels of the immune system:

1.  Physical and Chemical Barriers: This is stuff like your skin and mucous membranes that physically prevent antigens from entering the body.  There are also cilia, which are tiny hairs in your throat that make sweeping motions to force antigens outwards.  Different enzymes in your stomach also denature the protein structures of antigens.  Coughing, crying, vomiting, having diarrhea, etc. also physical expel antigens.

2.  Non-Specific Immunity:  If something does enter the body, many white blood cells called macrophages recognize them as foreign invaders by a protein marker on the plasma membrane that differs from the rest of the cells in the body.  Through phagocytosis, they engulf the antigens by extending their pseudopods (false feet) to almost wrap around the invader, then the lysosomes in the white blood cell break it down and put a piece of the invader on the plasma membrane of the white blood cell for the Helper T Cells and B Cells (all explain them in a  sec) to examine.  The cells that are involved in this second type of immunity do not differentiate between what type of foreign invader it is: as long as it is different from the rest of the body they will destroy it.

3.  Specific Immune Responses:  Cells in this type of immunity are programmed to fight a very specific type of disease.  For example, one T Cell might only be able to destroy one type of flu virus, whereas  another attacks only the polio virus.  The Helper T Cells take the small piece of the invader from the white blood cell (see above) and bring it to the Killer T Cells and the B Cells.  The Killer T Cells are then able to recognize the antigen and destroy it through lysing (literally destroying the plasma membrane, causing the cell to "pop".)  The B Cells are the cells that create antibodies, specific to a certain antigen.  These antibodies are released and can either lyse the antigen or neutralize it for the macrophages to come and engulf.

Hopefully, this helps, even though it is a very brief overview of a very complex topic!