Development of a simple procedure for the isolation of secretory IgA by lectin affinity chromatography and its clinical application.

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A lectin from jackfruit seeds ( Artocarpus integrifolia ) was first reported to be an LgA-specific binding lectin. We have collected several batches of jackfruit seeds from different countries, including the Phillippines, Singapore and Japan, and found that a batch of seeds from the Phillippines specifically bound human LgA of LgA1 subclass but not LgA2 subclass. The affinity column made from the LgA1-specific lectin ( jacalin-P ) could be used for the isolation of secretory LgA of LgA1 subclass. This column was also used for the separation of LgA1 and LgA2 of secretory LgA from conventionally purified human milk LgA. Analysis of sugar specificity of jacalin-P led to a conclusion that the oligosaccharide, Gal 1-3GalNAc, which is present in LgA1 hinge but is absent in LgA2 subclass, was responsible for the LgA1-specificty of the lectin.Among the lectins other than the jacalin-P, we found a lectin that bound every immunoglobulin other than LgA. Further analysis of this lectin ( jacalin-H ) disclosed that it also bound aggregated LgG and immune-complex. The use of jacalin-H affinity column efficiently removed the aggregated LgG and immune-complex as well as immunoglobulins other than native monomeric LgG from gamma-globulin preparations. The human gamma-globulin preparation thus treated was free from anti-complementary activity and will be applicable as a safe immunoglobulin preparation for various immune-deficient patients, including selective immunoglobulin deficiency, since it consisted of only native monomeric LgG.