In the midst of an anaphylactic / allergic reaction, your body perceives a molecule (antigen) as a threat, or scientifically an ‘allergen’. With the onslaught of Hay Fever drawing ever so closer as we approach summer, pollen will act as the allergen that your body wrongly recognises as a threat. Inhaled allergens can cause asthmatic attacks, or start to close airways in the worse case scenarios, while chemicals which come in contact with the skin and are absorbed and can cause hives, rashes, muscular pains and aches, nausea and pounding headaches.

This process is to do with a degranulation of Mast Cells. Mast cells (cells which occur in the tissue surrounding blood vessels and nerves) have the same interior composition as Endothelial cells for A level students, or the basic cell model for GCSE students, but have the properties of remaining inactive until they release (degranulate) their mediator molecules to take inflammatory action. Degranulate is a term for the mast cells releasing these ‘cyto-toxic’ (cell-toxic) molecules to destroy the allergen. Within the cell, visually, the molecules appear as a series of granules within the bigger, visual granules (actually called vescicles) and are released out of the granule through the membrane by binding to it, where the vescicle releases its contents.

These ‘granules’ are released when IgE (for A level students, this is immunoglobin E, an antibody produced by B cells that have become predisposed via T cells to the allergen) binds to the allergen and cross links with a FCεRI receptor on the cell plasma membrane, alerting the mast cell to the presence of the allergen. This signals the start of the degranulation process; releasing their inflammatory mediators (proteins: histamine, proteases, chekomines and heparin) which tend to cause Inflammation. Inflammation is important for several reasons:

– It helps to remove infectious agents from the site

– Plasma dilutes the pathogen, making them easier to deal with

– The extra white blood cells arriving at the site help to fight the infection

– The slight increase in heat can denature proteins and kill pathogenic cells.

This is followed by the introduction of newly formed mediators within the mast cells which attempt to regulate the level of foreign chemicals by directly destroying them. These new mediators include prostaglandins, leukotrienes, thromboxanes and platelet allowing factor (PAF): proteins which can cause:

-Airflow obstruction

-Increased secretion of mucus

-Constriction of the Bronchi.

-Infiltration of inflammatory cells in the airway wall

Anaphylaxis

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06holroydc@sjl.int – Cole Holroyd

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