The present invention provides a substantially purified carbohydrate ligand that specifically binds to a leczyme. The invention also provides methods to identify a carbohydrate ligand that specifically binds to a leczyme or a leczyme that specifically binds to a carbohydrate ligand. The invention further provides methods to identify a peptide that binds to the carbohydrate ligand binding site of a leczyme. The present invention provides methods to isolate a carbohydrate ligand or a leczyme and to identify a carbohydrate ligand or a leczyme that modifies the function of a cell and to obtain such functionally modified cells. The invention further provides methods to modify a cell to express a carbohydrate ligand by introducing an expression vector encoding a leczyme into the cell. The invention also provides methods to modulate the immune response to an antigen by administering the antigen and a carbohydrate ligand. In addition, the invention further provides methods to treat a disease state involving a leczyme by administering a carbohydrate ligand that binds the leczyme or by administering a leczyme that has a similar binding specificity to the leczyme involved in the disease state. The invention further provides methods to diagnose a genetic basis for hemochromatosis by detecting a mutation in a class I MHC molecule that reduces it's ability to associate with .beta..sub.2 microglobulin.