Parallel recognition of filarial antigens by IgE and IgG4 antibodies

IgE responses are highly modulated in human filariasis and allergic symptoms usually associated with IgE antibodies are seldom observed in individuals with Elephantiasis and Microfilaremia. Only a minor group with tropical pulmonary eosinophilia (TPE) suffer from nocturnal asthma. One possible mechanism may be the presence of IgG blocking antibodies which can block IgE mediated histamine release in vitro. Using immunoblot analysis we have further shown that remarkably similar pattern of antigen recognition were obtained with IgE and IgG antibodies which would be a major prerequisite for the blocking activity. In the present study, we have tried to determine if a particular IgG subclass is responsible for the parallelism seen with IgE antibodies. Immunoblotting with autoradiographic analysis was used to study IgE and IgG subclasses using highly characterized radiolabeled antibodies in 24 sera representing all three groups mentioned above. The most striking observation was that in 23/24 sera, the only antibody that showed consistent and parallel binding was IgG4. No consistent pattern of response was seen with any of the other three subclasses. IgG1 and 2 when present were usually directed predominantly to the high molecular weight antigens and were detected with greater frequency in Elephantiasis group. These results suggest that IgG4 may be an ideal candidate for the blocking activity seen in these sera. Such modulation of IgE responses may have important survival value for the host in filarial infection which tend to evoke rigorous IgE responses.