The normal function of CD23 is to act as a receptor for the Fc region of IgE molecules on the surface of mast cells and basophils. Its precise value to Toxocara canis is unresolved. It may help to make the parasite appear more “host like”. Alternatively, it may bind the Fc region of IgE antibodies that might ordinarily damage the parasite by binding it with
its Fab region.
It may be possible to develop a strain of T. canis in which the gene for production of the protein similar to CD23 is
inactive. Experimental animals might be infected with these worms and then inoculated with high levels of a soluble
form of CD23 which would bind up a large fraction of the available IgE. Since there would be little IgE available to
bind to the surface of the worms, any rapid destruction of the worms relative to controls could be attributed to the
inability to disguise themselves as “host like” rather than their ability to neutralize the effects of IgE.
An alternative would be to develop monoclonal antibodies against the Fc portion of the IgE antibody and administer
this to infected experimental animals that normally harbour the parasite. If the worms are destroyed it suggests that
the monoclonals interfered with the ability of the CD23-like protein to bind IgE Fc regions, and that it is Fc binding
that explains the protective value for the CD23-like protein for the parasite.
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