The potent IgG4-inducing antigen in banana is a mannose-binding lectin, BanLec-I.

IgG4 antibodies to banana were found to occur far more frequently than expected. The most important antigen involved proved to be a lectin, BanLec-I. Because of the lectin nature of the antigen, it was important to establish the antibody nature of the lectin-IgG4 interaction and to exclude an interaction between the sugar-binding site of the lectin and glycosidic chains on IgG4. Three arguments in support of immune binding are: (1) the binding of BanLec-I to IgG4 is mannoside resistant, whereas the binding to all other glycoproteins tested is mannoside inhibitable; (2) only a minor fraction of the IgG4 in serum and none of five IgG4 myelomas tested was bound, and (3) the lectin binds to the Fab fragment of the IgG4 molecule. A curious finding was that in the presence of high-molecular-weight glycoproteins the interaction between IgG4 and BanLec-I was enhanced by alpha-methyl mannoside. The probable explanation of this phenomenon is that complexes of the lectin with high-molecular-weight glycoproteins by sterical interference inhibit the interaction with human IgG4 antibodies (or with rabbit antibodies to the lectin). This inhibition is prevented in the presence of alpha-methyl mannoside. These results support the earlier suggestion that some lectins are particularly prone to induce an immune response upon oral feeding. This banana lectin might be a potentially useful carrier protein for oral antihapten immunization in humans.

Relationship between IgG1 and IgG4 antibodies to foods and the development of IgE antibodies to inhalant allergens. I. Establishment of a scoring system for the overall food responsiveness and its application to 213 unselected children.

To obtain reference levels for subsequent investigations, we analysed the IgG1 and IgG4 antibody levels to common foods in the sera of 213 unselected children (age 3 months to 14 years). The children were clustered into five age groups and tested on a broad screening panel of common foods. We used the IgG1 and IgG4 RAST with Sepharose-coupled antigens: cows' milk, hens' egg white, banana, legumes (a mixture of soybean and peanut), grains (a mixture of wheat and rice), potato, orange and pork. In all age groups and all antigens, a considerable variability in the antibody response was found. As for some assays more than half of the sera were negative or borderline, statistics based on interval or ordinal scaling were considered inappropriate and we resorted to nominal classification. We decided to use, for each of the assays, the 75-percentile of the age group as a cut-off level. Each antibody titre was thus converted into positive (more than the 75-percentile of that age group) or negative; the number of positive tests was used as the score. This resulted in a sigma G1-score and a sigma G4 score (summed scores for IgG1 and IgG4 antibodies, respectively). The results of the present study indicate that children with a high response to one food tend to have elevated responses to other non-related foods, possibly explained by a defective mucosal barrier and/or a hyperactive immune system. This suggests that a high-food responder phenotype may exist.

Relationship between IgG1 and IgG4 antibodies to foods and the development of IgE antibodies to inhalant allergens. II. Increased levels of IgG antibodies to foods in children who subsequently develop IgE antibodies to inhalant allergens.

In the present investigation we have tested the hypothesis that children with a high IgG antibody response to foods have an increased risk of developing IgE antibodies to inhalant allergens. Sera from 106 children with an increased risk of developing IgE-mediated allergy were analysed. During the follow-up, in 54 of these children IgE antibodies to inhalant allergens appeared. A positive/negative IgG1 and IgG4 anti-food score was determined as described previously: sera from age-clustered unselected children were tested for the levels of IgG1 and IgG4 antibodies to common foods. For each IgG RAST and each age group, the 75-percentile was chosen as cut-off value. Each antibody level was thus converted into a positive (higher than the 75-percentile of the age group) or negative value. The number of positive tests was used as the score. High-risk children with a high IgG1 anti-food score more often developed inhalant-specific IgE antibodies than high-risk children with low IgG1 titres: 50% of the children with a high IgG1 anti-food score developed IgE antibodies to grass pollen. Fifty per cent of the children with a high and 14% of the children with a low IgG1 anti-food score developed IgE antibodies to cat dander. For the prediction of the development of IgE anti-mite (house dust mite), the IgG4 anti-food scores appeared less useful than the IgG1 anti-food scores; 46% of the IgG4 high responders versus 22% of the IgG4 low responders acquired IgE anti-mite, whereas for IgG1 these percentages were 73 and 19, respectively.

Isolation and characterization of BanLec-I, a mannoside-binding lectin from Musa paradisiac (banana).

A lectin (BanLec-I) from banana (Musa paradisiac) with a binding specificity for oligomannosidic glycans of size classes higher than (Man)6GlcNAc was isolated and purified by affinity chromatography on a Sephadex G-75 column. It did not agglutinate untreated human or sheep erythrocytes, but it did agglutinate rabbit erythrocytes. BanLec-I stimulated T-cell proliferation. On size-exclusion chromatography, BanLec-I has a molecular mass of approx. 27 kDa, and on SDS/PAGE the molecular mass is approx. 13 kDa. The isoelectric point is 7.2-7.5. BanLec-I was found to be very effective as a probe in detecting glycoproteins, e.g. on nitrocellulose blots.

Cross-reactivity of IgE antibodies to caddis fly with arthropoda and mollusca.

We investigated the possibility that subjects with IgE antibodies to an inhalant insect allergen, such as caddis fly, might also have antibodies to cross-reacting carbohydrate determinants (CCDs). IgE antibodies to cross-reacting allergens in caddis flies, mussels, oysters, shrimps, crabs, honeybee, and yellow jacket venoms were determined by RAST, RAST inhibition, and immunoblot studies with sera from three different sources: (1) sera of patients with well-defined inhalant atopy to caddis fly, (2) sera with IgE anti-CCD antibodies from subjects without known exposure to caddis fly, and (3) hyperimmune antisera with IgG anti-CCD antibodies raised as a result of immunization of rabbits with grass-pollen extract, buckwheat glycoprotein, or with honeybee venom. Sera from groups 2 and 3 reacted with Sepharose-coupled caddis fly extract in a RAST-type assay and elicited virtually identical patterns on immunoblots of caddis fly extract separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas the sera from group 1 atopic patients did not react with CCD-rich material. However, indications for other types of cross-reacting antibodies were detected. The IgE antibodies of one of the patients studied (who was allergic not only to caddis fly but also to shellfish) were found to detect a cross-reacting homologous protein in extracts of mussel, oyster, shrimp, crab, honeybee, and yellow jacket venom. Preliminary results suggest that this cross-reacting 13 kd protein, the most prominent caddis fly allergen, is an invertebrate hemoglobin (erythrocruorin)-like molecule. These studies suggest the possibility that patients sensitized by exposure to caddis fly antigens could develop allergic reactions during their first exposure to shellfish or to their first bee sting.

Cross-reactivity among birch pollen, vegetables and fruits as detected by IgE antibodies is due to at least three distinct cross-reactive structures.

Sera of patients suffering from birch pollinosis were studied in the radio-allergo-sorbent test (RAST) for the presence of IgE antibodies to various allergens of vegetable origin. The sera selected were positive in the RAST for both birch pollen and fruits. IgE antibodies directed against at least three different cross-reacting determinants in birch pollen were detected. In addition to periodate-susceptible cross-reacting determinants, which are found on a number of glycoproteins, two non-related periodate-resistant determinants were found in birch pollen, with molecular weights of 20 and 18 kD, respectively. The 20-kD component appears to be responsible for the co-occurrence of the binding of IgE to allergens of fresh fruits, whereas the 18-kD component appears to cause the cross-reactivity among grass pollen, potato and fruits.