Specific IgE and IgG
With the discovery of IgE in the 1960s, measurements of IgE have been a first step in diagnosis for atopic diseases. Both allergen-specific IgE (sIgE) and total IgE levels increase during the initial stages of AIT and subsequently decrease,229 however, decreases may not accompany a positive clinical outcome.230 Numerous studies indicate IgG1 and IgG4 levels increase with therapy but do not always differentiate between responders and non-responders. IgG4 increases during AIT may reflect compliance not clinical efficacy.230 sIgG4 is purported to be a blocking antibody by competing for allergen binding with IgE bound to Fcε receptors on mast cells and basophils, preventing degranulation. IgA and other subclasses of IgG may have similar blocking function.231 Recent data support skewing towards IgG2 and IgG4 subclasses after SLIT for temperate grass pollen.181 The IgG4/IgE ratio may monitor AIT progress and outcome, but has demonstrated conflicting utility.232-234 Flow cytometry-based assay (IgE-FAB) and a solid-phase assay enzyme-linked immunosorbent-facilitated antigen binding (ELIFAB) assay can determine IgE-inhibitory activity. Although robust with good clinical efficacy correlation for AIT, these technologies are complex with usage limited to specialized centers.230,235,236