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The W14 (MaKi) specificity of the FOUR locus is positively associated with a previously unrecognized specificity of the LA locus, which is now provisionally called Fe 55. Because of the similar and low frequency of the two antigens, the recognition of Fe 55 as a separate entity is very difficult. It is possible that the same phenomenon is delaying the recognition of other “blanks'’ as well.
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Ferrara et al. (1973) studied this question.
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