Homocytotropic antibody in sheep

It has been possible to demonstrate, using the homologous passive cutaneous anaphylaxis (PCA) reaction, the presence of homocytotropic (reagin-like) antibody in the sera of sheep infected with Ostertagia. The presence of antibody was detectable with Evans blue dye, and a radiolabelled 131I technique. The antibody appeared to fulfil the criteria for homocytotropic antibody, and reacted with an allergenic extract (molecular weight 20,000–50,000) of Ostertagia. An in vitro radio-allergo-absorption method using IgG1A (a new sheep immunoglobulin sub-class) failed to detect homocytotropic antibody, although the Fc fragment of goat anti-sheep IgG1A was capable of blocking the PCA reaction, and of producing a reversed-type allergic skin reaction. This homocytotropic antibody is probably associated with the `self-cure' reaction in Ostertagia infection.