The molecular biology of selected phagocyte defects

Advances in molecular genetic understanding of disease processes has been extended to a number of phagocytic disorders. Most of these disorders were extensively characterized at the functional and protein level prior to cloning of the relevant genes. Nucleotide sequence data has been essential for establishing the mechanism and mode of inheritance of genetically transmitted phagocyte disorders. Such data provides insights into the functionally important regions of affected proteins and information regarding regulation of these genes and homologies to other known proteins. From such data it is also possible to determine the evolutionary history of these genes. Chronic granulomatous disease, a phenotypic classification of a heterogeneous group of defects in oxidative metabolism, has now been defined in terms of specific molecular defects. Cloning of the two subunits of cytochrome b558 has led the way to characterization of the X-linked form and one of the autosomal recessive forms of this disease and confirmed the importance of this protein in the phagocyte oxidative burst. The absence of lactoferrin associated with hereditary specific granule deficiency is a result of decreased transcription of the lactoferrin gene in myeloid cells. Myeloperoxidase deficiency is likely a result of a mutation of the gene coding for myeloperoxidase. More precise understanding of expression of the lactoferrin and myeloperoxidase genes may be important in elucidating some of the underlying mechanisms in the pathogenesis of myeloid malignancies. A rare disorder, leukocyte adhesion deficiency, has provided a model for establishing the relationship between the several distinct alpha subunits and the shared common beta subunit of leukocyte adhesion proteins. These proteins have been shown to be genetically related to the superfamily of extracellular matrix receptors termed 'integrins'. Because these proteins have been highly conserved at the genetic level across a variety of species, comparison of nucleotide sequence data has illuminated some of the evolutionary history of these genes as they arose from ancestral genes. Studies of these adhesion protein genes may contribute new information in the broader context of how the functions of these genes evolved.