In this paper one of the most important human DC is referred to as pDC[assuming 'p' means protective]. This specialised cell acts to investigate and then teach the immune system to tolerate antigens such as from house dust mites.
In an alternative pathway, and depending upon signalling from lung cells, educated DC can skew the immune system towards an allergic response. Below is a simplified version of this pathway. Apologies to the author.
1. Inhaled products, including those from dust mites, can encourage epithelial cells to signal and activate sentinel DCs. In this article, this innate immune information transfer is referred to as a 'conversation'. Both epithelial cells and educated DC have receptors or sensors that act to give a warning of potential or real harm.
2. An invasive mite allergen can directly encourage a DC to make an inflammatory response through cysteinyl leukotrienes, via a dectin 2 mechanism. Dectin 2 is a specialised trigger located on the surface of a DC.
3. Once taken up, the mite's allergen can induce DCs to migrate to pulmonary lymph nodes thus contributing to a Th2 allergic response.
4. DCs, circulating in pulmonary vessels, are able to pass through the blood vessel walls to defend the delicate gas exchange area of the lungs against an attack.
All the above activity can trigger or enhance inflammation.
One of the most interesting comments and implications from this review is; 'Increased IgE levels are linked to impaired DC antiviral responses. This might explain the enhanced susceptibility of atopic subjects to virus-induced wheezing. as well as indicate new therapeutic approaches.'
Please forgive this simplistic explanation of a comprehensive scientific paper. It is a 'must read' for scientific researchers interested in DC activity in asthma.
Mechanisms of allergic disease: 'The role of dendritic cells in asthma', Gill MA, 'J Allergy Clin Immunol'. 2012;129:889-901