Heterogeneity in the molecular defect leading to the leukocyte adhesion deficiency

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Abstract
Leukocyte adhesion deficiency (LAD) is a recessive autosomal disease characterized by life‐threatening recurrent bacterial infections, by defective functions of leukocytes and by deficient membrane expression of leukocyte adhesion glycoproteins. These proteins, LFA‐1, Mac‐1 and p150,95, are α/β1 heterodimers composed of different a chains and of a common β chain. Patients with the severe phenotype of the disease completely lack the three glycoproteins on cell surface. Previous studies showed a conserved synthesis of the LFA‐1 α chain precursor in cytosol of patients' cells and an inconstant presence of the β chain precursor. When present, precursors are in free form and not associated to α/β complexes in the cells of patients with the severe phenotype. The availability of the β chain cDNA probe allowed us to examine the β chain gene expression in the lymphoblastoid cell lines of 4 patients. On the basis of the results obtained both at protein and RNA levels we can distinguish 3 types of mutations characterized by (a) barely detectable β subunit messenger RNA and un‐detectable β precursor, (b) decreased level of β subunit mRNA and undetectable β precursor and (c) normal β subunit mRNA level and detectable p precursor of normal size.

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