As described in Chapter 15, cell-surface molecules belonging to the integrin family of proteins function as adhesion molecules and are required to facilitate cellular interaction. Three of these, LFA-1, Mac-1, and gp150/95 (CD11a, b, and c, respectively) have a common p chain (CD18) and are variably present on different monocytic cells; CD11a is also expressed on B cells (Table 19-2). An immunodeficiency related to dysfunction of the adhesion molecules is rooted in a defect localized to the common p chain and affects expression of all three of the molecules that use this chain. This defect, called leukocyte adhesion deficiency (LAD), causes susceptibility to infection with both gram-positive and gram-negative bacteria as well as various fungi. Impairment of adhesion of leukocytes to vascular endothelium limits recruitment of cells to sites of inflammation. Viral immunity is somewhat impaired, as would be predicted from the defective T-B cell cooperation arising from the adhesion defect. LAD varies in its severity; some affected individuals die within a few years, others survive into their forties. The reason for the variable disease phe-notype in this disorder is not known. LAD is the subject of a Clinical Focus in Chapter 15.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.