T07036: Development, recognition and significance of IgG antibodies in allergic sensitisation and adverse reactions

Study Duration: January 2003 to June 2004

Contractor: St Mary's Hospital, Manchester

At present the evidence for the direct involvement of IgG antibodies in food allergy is controversial and remains unresolved. This study is measuring peanut specific IgG from patients with sensitivity to peanut in order to establish if IgE and IgG antibodies develop in parallel and determine the extent to which the antibody classes share common epitopes for a major peanut allergen.

The first section of work involves comparing the levels of peanut specific IgG in anonymised archive samples from patients who have previously experienced a range of reactions to peanut.

Any direct or indirect role of IgG, or a particular IgG subclass, in allergy will be assessed by linking results to both the clinical and laboratory information available in the FSA-funded Research Allergy Database.

The second section of work will retrospectively investigate the development of peanut specific antibodies in children. The aim is to determine if IgG antibodies change in parallel with other classes of peanut specific antibodies. This will include studying whether IgE and IgG antibodies can recognise the same linear peanut protein sequences.

Background
At present the evidence for the direct involvement of IgG antibodies in food allergy is controversial and remains unresolved. This study was aimed at measuring peanut specific IgG antibodies from patients who are allergic to peanut in order to establish if IgE and IgG antibodies develop in parallel and to determine the extent to which the antibody classes share common epitopes (antigen binding sites) for a major peanut allergen.

Research Approach
The first section of work involved comparing the levels of peanut specific IgG in anonymised archive serum samples from patients who had previously experienced a range of reactions to peanut.

The role of IgG, and particular IgG subclasses, in allergy, was assessed by linking results from analysis of serum samples to both the clinical and laboratory information available on the subjects via the FSA-funded Research Allergy Database.

Peanut allergic subjects, identified from the clinic’s nut allergy database, were classified into “mild” or “severe” groups, depending on whether they had experienced “mild” or “severe” reactions to peanut in the past.

The results to the first part of the study confirmed that peanut allergic individuals in the “severe” group had a higher level of peanut specific IgE than those in the “mild” group. Analysis of the peanut specific total IgG levels in these patients showed no significant difference between the two groups. However, patients in the “severe” group were found to have a three-fold lower IgG:IgE ratio than patients in the “mild” group. The researchers hypothesised that one reason for the observed lower IgG:E ratio in the “severe” group might be that IgG could compete with IgE for binding sites on the surface of an allergen in these patients. It could be that there is insufficient IgG in these “severe” subjects to block IgE from binding to the allergen and resulting in the symptoms of an allergic reaction.

Analysis of the individual IgG subclasses of these same patients showed that levels of IgG4 were significantly higher in the patients who experienced “severe” reactions than those with “mild” reactions, however the clinical significance of this observation is unkown. No significant differences in the levels of the other IgG subclasses (IgG1, IgG2, or IgG3) were detected.

The second part of the study investigated the development of peanut specific antibody responses over time, and whether IgE and IgG antibodies recognise the same peanut protein sequences.

Analysis of peanut specific antibody responses over time showed that peanut specific IgG levels tended to be significantly raised soon after an allergic reaction and were lower a year later, whereas peanut specific IgE levels did not alter. Longer term studies conducted on stored serum samples did not elucidate any clear pattern in the appearance or changes in the level of peanut IgE or IgG antibodies, in peanut allergic children.

The final report is available from the Agency’s Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency
tel: 020 7276 8181/8182
email: library&infocentre@foodstandards.gsi.gov.uk

For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk