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