Impaired culture generated cytotoxicity with preservation of spontaneous natural killer-cell activity in cartilage-hair hypoplasia.

Recent studies of cartilage-hair hypoplasia (CHH), a form of short-limbed dwarfism, have shown that all affected individuals have a cellular proliferation defect that results in a cellular immunodeficiency. However, only a minority of CHH individuals suffer from severe, life-threatening infections. For this reason, relevant immune defense mechanisms that may be responsible for maintaining intact host defenses in the majority of CHH individuals were studied. Spontaneous and allogeneic culture-induced (mixed lymphocyte response-MLR) specific and nonspecific (NK-like) cytotoxic mechanisms were analyzed and correlated with lymphocyte subpopulations present in CHH and normal individuals. Spontaneous natural-killer (NK) activity was present at or above normal levels, but culture-induced specific cytotoxicity and NK-like cytotoxicity as well as NK-like activity by T cell lines were significantly reduced in CHH individuals. The generation of radiation-resistant cytotoxicity, which normally occurs during allogeneic MLR, was markedly diminished in CHH, and was correlated with the decreased proliferation observed in CHH cultures. Preservation of spontaneous NK activity and loss of all forms of culture-induced cytotoxicity was associated with an increase in the proportion of lymphocytes bearing a thymic independent NK phenotype (OKM1+ OKT3- Fc gamma + low-affinity E+), and a significant decrease in thymic derived OKT3+ cytolytic T cell sub-populations in CHH individuals. Therefore, an intact cellular cytotoxic effector mechanism has been identified in CHH (i.e., NK activity). Natural cytotoxicity may be of importance in maintaining host resistance to viral infections despite diminished thymic-derived effector mechanisms in cartilage-hair hypoplasia.