Leukocytes, or white blood cells, are a major component of the body's immune system. White blood cells fight against infections within the body.
Leukocyte adhesion deficiency (LAD) is a very rare genetic disorder that impairs the body's immune system, making the patient susceptible to recurrent infections. LAD is considered a primary immunodeficiency (PI) and it is not contagious. Primary immune deficiencies, unlike secondary immune deficiencies, occur because part of the body's immune system does not function properly. These disorders are caused by intrinsic or genetic defects in the immune system.
LAD occurs when a patient's body is unable to produce glycoproteins that are found on the outside of leukocytes. These glycoproteins enable the leukocytes to adhere to the blood vessel walls as they migrate towards sites of inflammation during a process called chemotaxis.
There are two different genotypes that cause the disease - type I and type II.
LAD I is characterized by recurrent bacterial infections, defects in neutrophil adhesion and a delay in umbilical cord sloughing (shedding). Defects in adhesion prevent the neutrophils from congregating toward a site of infection (chemotaxis) and from performing phagocytosis (process of engulfing harmful microbes that enter the body). Most LAD I patients die by age five, unless they are successfully treated with a bone marrow transplant. Bacterial infections are responsible for most deaths. However, patients who experience moderate symptoms may survive into young adulthood without a transplant.
Patients who have LAD II do not usually die from infections. LAD type II patients typically have severe mental retardation, neurologic impairment, and short stature. Dental periodontitis (inflammation of the gums) and rarely colitis (inflammation of the large intestine) may be found in older individuals.
Fewer than 200 cases of LAD I have been reported worldwide in medical literature. However, the actual number of cases may be higher because little is known about the disorder. LAD II is even rarer, with only a handful of reported cases worldwide.
Dogs and cattle have also been diagnosed with the disease. The type that affects dogs is called Canine LAD, or CLAD. The type that affects cattle is called Bovine LAD, or BLAD.
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leukocyte adhesion during inflammation
When inflammation occurs in the body, a signal is sent out from the affected area to the blood vessels where leukocytes reside. In a healthy person, the leukocytes receive the message, activate, and begin to move toward the infected area by adhering to the blood vessel wall with CD18, a glycoprotein that surrounds the cell. This process is called chemotaxis.
The leukocytes in individuals who have LAD are unable to adhere to the blood vessel walls once they are activated because they lack the necessary glycoproteins, such as CD18 or CD11.