Cross-reacting carbohydrate determinants

This and other observations indicate that the 5.7 S protein lacks a large portion of the Fc region of the 7.8 S molecule. It has a very low carbohydrate content (0.6%) as compared to 5.0% for the 7.8 S molecule. The molecular weights of the H chains of the 5.7 S and 7.8 S proteins are 35,000 and 62,000, respectively (102). Antibody specific for the H chain of chicken IgG cross-reacts strongly with duck 7.8 S immunoglobulin but hardly at all with duck 5.7 S protein this is consistent with the possibility that the cross-reactions involve Fc determinants. Finally, the 7.8 S, but not the 5.7 S molecule, is able to fix duck complement (100,101). 

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