Allergens

A. fumigatus produces a considerable number of allergenic molecules, including at least 23 identified proteins (Asp f 1-Asp f 23) and polysaccharides (Kurup, 2005). Among them are several secreted enzymes (Asp f 10/PEP, Asp f 13/Alp2, Asp f 5/MEP) which are associated with host invasion. Interestingly, most of the other allergens are not predicted cell wall or secreted molecules (i.e. Asp f 8 and Asp f 23 ribosomal proteins, Asp f 12 hsp90 family, Asp f 22 enolase). One possibility is that these abundant cytosolic proteins are released from the fungus following damage by the immune system. Another is that these proteins may be naturally present at the cell surface and have some unknown role (e.g. energetic role, antigenicity, surface receptors) (Lopez-Ribot et al., 2004).

Allergies inflicted by A. fumigatus include asthma, ABPA, allergic fungal sinusitis, and hypersensitivity pneumitis. They occur in hypersensitive individuals as a result of excessive IgE-mediated mast cell degranulation and eosinophilic infiltration and tissue damage in response to inhaled A. fumigatus allergens (Figure 8.1B). Both humoral (elevated antigen specific IgG, IgE, and IgA) and cell-mediated immunity (Th-2 cell cytokine secretion) are activated. Some of the A. fumigatus allergens identified could be useful for diagnosis of ABPA. Allergen-specific immunotherapy should be developed to induce tolerance in susceptible hypersensitive individuals.

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