Human interferons have been classified into 3 groups: alpha, beta, and gamma. Both alpha- and beta-IFNs, previously designated type I, are acid-stable, but they differ immunologically and in regard to some biologic and physiochemical properties. The IFNs produced by virus-stimulated leukocytes (leukocyte IFNs) are predominantly of the alpha type. Those produced by lymphoblastoid cells are about 90% alpha and 10% beta. Induced fibroblasts produce mainly or exclusively the beta type. The alpha- and beta-IFNs differ widely in amino acid sequence. The gamma or immune IFNs, which are produced by T lymphocytes in response to mitogens or to antigens to which they are sensitized, are acid-labile and serologically distinct from alpha- and beta-IFNs. (from OMIM 147570) [ ]