>Tardigrades: No comment.

>The immune system: The most awesome thing ever.

It's actually two systems. One called the innate that we have in common with most forms of complex life, and the adaptive immune system, something we've only seen manifested in jawed vertebrates.

The innate immune system is a set of cellular signals/behaviors that are triggered by cells being exposed to damage and or stress.

These responses are generalized. Just about anything odd can invoke them, so they are typically the first line of defense. These include things like alteration of permeability of the local extracellular matrix (swelling), formation of impermeable tissue barriers to isolate damage (cysting, compartmentalization), and setting up signaling molecule gradients that attract phagocytic/cytotoxic cells to the terminate anomalous cellular activity/clean up the place (macrophage attraction), and alteration of metabolic activity to generate thermal stress (fever).

The issue with the general immune system though, is that it's non-specificity and versatility makes it a bit like a sledgehammer in the context of a complex organism. It can do as much or more damage as it can do good, and it isn't that good at only eradicating the exact thing causing the issue without excessive collateral damage.

Enter the adaptive immune system. The adaptive immune system is composed of various cell lines, and organ systems all specialized into dealing with specific facets of an immune response, and mediated through a set of special cellular surface receptors.

The facets of the adaptive immune response are: antigen recognition, coordination, moderation, and memory.

The major cell lines are T and B cells. T cells are further broken down into cytotoxic T, and helper T cells.

The adaptive immune system starts with naive lymphocytes. These cells rapidly multiply randomizing the ever loving crap out the region of the genome dedicated to the MHC receptor. By doing this, it'll cause the receptor to fold in ways that will allow it to bind with certain types of antigen (think of it as the antigen's key fitting the Mac's lock.) This proves of new receptor generation is mediated by the Thymus. The thymus tests every new variant to see whether there is any sensitivity to proteins that may expressed in other parts of the body. If it finds that to be the case, itinduces that particular cell to suicide to prevent the proliferation of immune cell lines with a high chance of being prone to autoimmunity. Those that survive are allowed to move out into the lymphatic and circulatory systems to patrol for their particular antigen. Upon meeting it, a few things happen. First off, the immune cell can help kick off or amplify a general immune response. Secondly, signaling proteins are released to attract more leukocytes to the area. Third, an antigen bearing cell will migrate toward the Thymus to recruit more immune cells. Once an antigen presenting helper T cell binds with a compatible B or Cytotoxic T cell line, that cell line undergoes massive replication without further modifying it's receptor, and the helper T cell does likewise.

B cells will create and secrete antibodies. Small snippets of protein that will bind to and foul up the workings of the antigen to which the are sensitive.

Cytotoxic T cells will patrol for and engulf antigen it encounters, either breaking it down with a burst of oxidative substances, or if the antigen is detected being presented on a cellular membrane protein, and a helper T cell is near by to enable the response, a cytotoxic T cell can induce cell death of an antigen presenting cell, but with much greater specificity and numbers than the mechanism used by macrophages. Once the cell death takes place, the cell will either clean up the remains, or attract macrophages to do so while it heads off for the next target.

The cytotoxic T cells are handicapped in their destructive potential by the need for a nearby Helper T cell. B cells just shotgun anti-antigens into the blood stream.

>Medications: oh dear God askapharmacologist. The closest I have committed to memory, is that most pharmaceuticalsarea veryspecifically formulated chemical intended to be able to be absorbed without difficulty, being capable of making their way to a target area in the body, modified to an active form by enzymes in the body to do their thing before eventually getting degraded and excreted by more of the same.

Plastics: no comment.