The switch region and membrane exons of the invention may comprise a human gamma 2 constant region and {HEAD ~ the secreted constant region exons} are from a human gamma 1 or {TAIL ~ a human gamma 4 constant region} 
The switch region and membrane exons of the invention may comprise a human gamma 2 constant region and { HEAD ~ the secreted constant region exons } are from a human gamma 1 or { TAIL ~ a human gamma 4 constant region }
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