Bovine leucocyte adhesion deficiency: a review of a modern disease and its implications

Bovine leucocyte adhesion deficiency (BLAD) is a genetic disease of cattle which affects the hematopoietic system. In the last decade BLAD has become a disease of economic importance in the dairy industry. This review describes the chronological developments and thinking that led to the elucidation of BLAD as a disease distinct from previous models in canine and human populations. All species affected show signs of chronic and recurrent infections. Necrotic and/or gangrenous infections of soft tissues are prevalent, in addition to secondary infections with bacteria or fungi. Low birthweight and unthriftiness are key signs in all species affected by leucocyte adhesion deficiency (LAD). Dermatomycoses and impaired pus formation are also common findings. The physiological basis for BLAD is a deficiency in the chemotactic and phagocytic properties of leucocytes and particularly neutrophils. The inhibition of diapedesis in the inflammatory response prevents normal immune reactions to invading pathogens. Chronic infections are a consequence of the faulty immune mechanisms. The biochemical aetiology of BLAD involves cell surface glycoprotein molecules known as integrins. These are responsible for the cell-cell interactions necessary for neutrophils to adhere to vascular endothelium in a normal individual. Experiments with monoclonal antibodies to block LFA-1, Mac-1, and p150,95 (three integrins vital for cell-cell interactions) mimic BLAD symptomatology and have led to the discovery of the reciprocal intercellular adhesion molecule (ICAM). Through pedigree analysis and biochemical detection with restrictive endonucleases, BLAD has been isolated genetically to a single gene locus. The economic significance and prophylaxis of the disease are briefly discussed. In addition, the beneficial aspects of the study of BLAD are considered. There are advantages in producing a BLAD-like state for preventing transplant rejection, ischaemia-reperfusion injury and other problems arising from the deleterious effects of the inflammatory response.