Preliminary investigations on abnormal immunoglobulin(s) in leprosy.

A new, abnormal immunoglobulin designated IgK has been discovered in leprous Rubino-negative sera. The IgK having a negative net charge and its own antigenic specificity appears to be partly related to the Fc fragment of IgA and to Fab fragments of known immunoglobulins, but its net charge is negative at pH 8.8. Its molecule seems to possess kappa but not lambda light polypeptide chains. Implications of this discovery are discussed.