In a randomly selected group of coeliac patients, alpha-gliadin antibodies (AGA) of
subclasses IgG1 and IgG3 were significantly elevated (p less than 0.01) in comparison
to both normal and disease control groups. This result was, however, influenced by
increased total AGA levels in the coeliac patients. AGA subclass profiles of cohorts
of coeliac and normal controls matched for total IgG AGA were therefore compared.
It was found that IgG3 AGA levels were higher in the coeliac group (p = 0.006) while
IgG4 titres were higher in the control group (p = 0.005). Titres of IgG1 and IgG2
AGA did not differ between the two groups. Because of the marked differences between
the ability of IgG3 and IgG4 to activate complement, alpha-gliadin-specific complement
fixation was measured. Using randomly selected coeliac and normal sera, the patient
group activated highly significantly greater quantities of complement than controls
(p less than 0.01). Furthermore, when samples matched for total IgG AGA were compared,
sera from coeliac patients were again found to activate greater amounts of complement
than sera from controls (p = 0.024). Thus AGA in coeliac sera are both structurally
and functionally distinguishable from AGA in normal control sera.