Serum interferon in Navajo children with severe combined immunodeficiency disease inhibits lymphoblastogenesis

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Abstract
Two Navajo Indian children with severe combined immunodeficiency disease (SCID) lost reconstituted immune function after virus infections. A serum factor which inhibited normal lymphocyte response to mitogens was found in one of them and led to the examination of sera from five other Navajos with SCID. Mean inhibition by six Navajo sera was 67%; no inhibitor was found in sera from normal adults and children. The inhibitor activity was nondialyzable and heat stable, yet partially sensitive to pH 2.0, suggesting that interferon(s) was present. Interferon (IFN) activity in patient sera ranged from 10 to 300 U/ml. Normal children had peak serum IFN levels of 100 and 30 U/ml in the acute and convalescent periods, respectively, of virus infections. IFNα, IFNβ, and IFNγ were identified in SCID sera by specific antisera. Both inhibitor and IFN activities in three Navajo sera were 88–95 and 89–100%, respectively, removed with anti-IFN antisera. Similar patterns of inhibition of lymphoblastogenesis were seen with IFN standards. IFN levels in the SCID patients did not correlate with documented infections; elevated levels were present when no infections could be documented. The immunologic imbalances in some forms of SCID may be related to circulating inhibitors, possibly interferon.