Welcome to the early days of spring! After a long winter, we’re ready for brightly colored blooms and buds, less clothing layers, and more daylight. Several of us are also preparing for the inevitable start of spring season allergies. Allergies are hypersensitive disorders of the immune system. Normally, the immune system only reacts if a harmful substance attacks the body. However, with allergies, the immune system reacts to a relatively harmless substance, such as pollen. Below is a play by play of what happen in the body during an allergic reaction.
Day 1: Sensitizing Exposure
STEP 1: The Allergen enters the body and encounters a lymphocyte cells. Lymphocytes are the custom agents of the body; their job is to check the passport of every cell they encounter.
STEP 2: The lymphocyte cell registers the particle or cell surface marker as threatening.
Any particles/cell surface markers that provoke an immune response are called antigens, short for antibody generator (see next step).
STEP 3: The lymphocyte cell heads to the nearest lymph node where it produces a type of antibodies known as immunoglobulin E (IgE).
Antibodies are proteins with a distinct Y shape that contain a very specific match to the threatening antigen. (To learn about antibodies check out this post.)
STEP 4: IgE antibodies attach themselves to mast cells throughout the body.
Mast cells are defined by the presence of a large amount of chemical mediators such as histamine. Antibodies prepare mast cell to release these mediators. (Using SAT terminology, fuse is to bomb as IgE is to mast cell.)
Days, weeks, or year later: Allergic Reaction
STEP 1: The allergen/antigen re-enters the body, encounters its matching IgE antibody, and binds to it.
Antibodies bind with antigens through a combination of forces (electrostatic, hydrogen bonds, hydrophobic interactions, and van der Walls forces.)
STEP 2: The IgE –antigen complexes trigger the mast cell to releases granules of powerful chemical mediators.
There are about 30 but the most famous and it seems most effective are histamines and leukotrienes.
STEP 3: Histamine and other mediators flow through the body causing irritation of certain nerve endings (itchy skin, eyes, and nose), leakage of fluid (runny nose and hives), and the contraction of smooth muscles (shortness of breath and possibly tracheal closure).
Some mediators act immediately while others can take hours to have an effect. The result of the latter is a late phase allergic reaction where symptoms appear four to six hours after the exposure.
During spring, wind-pollinating (anemophilous) trees are the principle culprits behind our allergies. Eventually, the level of pollen produced by these trees will decrease over time and symptoms will subside. Thankfully the antigen-antibody interaction is very specific and each plant genus produces pollen that is morphologically distinct. This means that an allergy to one pollen type does not imply an allergy to all pollens.