What is an allergy?
Although all the details are not completely understood, current evidence allows us to construct the likely pathway to allergy. Allergy starts with a person who has a susceptibility to develop allergy. Individuals vary in their sensitivity to different types of substances and the degree to which they have a reaction.
For fungal allergy, a person inhales small amounts of fungal spores into the respiratory tract. These spores release soluble proteins (some of which are allergens) which can be internalized by B-cells bearing IgE antibody on their surface that reacts to a portion of a specific fungal allergen (B-cell epitopes).Free floating IgE can also bring allergens to other types of antigen-presenting cells. The allergens are then processed inside both of these cell types and presented as small peptides on the surface on MHCII molecules. The display of certain peptides (T-cell epitopes) leads to contact with specific T-cells that express a T-cell receptor that binds to a specific MHCII-peptide complex.
This leads to T-cell activation. When activated T-cells recognize a corresponding B-cell in this manor, the T-cells produce cytokines that cause the proliferation of the corresponding B-cells, leading to sustained production of IgE that reacts to specific fungal allergen epitopes. Patients can develop IgE reactions to multiple allergens via different T-cell and B-cell clones that recognize different allergens. The IgE molecules attach to certain types of cells (mast cells) located in the respiratory mucosa. When exposed to future allergens in the respiratory tract, these allergens will crosslink the IgE and cause the release of active chemicals (degranulation) that leads to a variety of symptoms. Symptoms can vary from mild allergic rhinitis to severe asthma.
In normal, non-allergic patients, it is believed that such minor exposure as described above does not lead to immune reaction and the production of allergic amounts of IgE. In normal reactions, an exposure that leads to an immune response causes the IgE producing clones to shift to IgG production or to be deleted. Allergy can be described as a hypersensitivity reaction.