Hypersensitivity sounds like you cry at too many Cameron Diaz movies (does that reference date me enough? No one else was coming to my mind). In medical terms, though, hypersensitivity is something totally else, as if you didn’t guess that.

Essentially, what happens is the body gets infected or has some sort of foreign pathogen or even just material of some type. When the immune system mounts it’s response, it goes a little overboard and gets confused. The body then starts attacking itself. To call it an over-reaction is a little bit of an over-simplification, but it does get the the general idea.

We categorize Hypersensitivity reactions into 4 categories: I, allergy/immediate; II, cytotoxic/antibody dependent; III, immune complex disease; IV, delayed type/cell mediated/antibody independent.

Those actions or pathways are the main differences between the hypersensitivities, but you can also generally do it by the mediators that are involved: I, IgE; II, IgM and IgG, complement or MAC; III, IgG, complement and neutrophils; IV, T-cells.

The best way to understand the different types of hypersensitivities, though, is to have a grasp of the underlying faulty mechanism that happens in each category. If you can get that, it will make sorting the various diseases and syndromes into the appropriate category much easier.

Starting next week, we’ll go through each one and spend time on them to make sure we can do that!