Luisa was born at full term and was the second child born to the
Ortegas. At 4 weeks of age, she was taken to her pediatrician
because of swelling and redness around the umbilical cord and a
fever. Her white blood cell count was 71,000 uL-1 (normal is
5000-10,000 uL-1). She was treated with intravenous antibiotics and
discharged with a WBC count of 20,000 uL-1. The Ortegas had a baby
boy 3 years before Luisa’s birth. At 2 weeks of age, he developed a
very severe infection of the large intestine. He suffered from
multiple infections and died of pneumonia at 1 year of age. Because
of this family history, Luisa was referred to Children’s hospital
for further testing. Fluid cultures were all negative. Her WBC
count was 68,000 uL-1. The composition of WBC was normal, as was
her complement components and her serum immunoglobulins. A Rebuck
skin window was performed in which the skin of the arm is gently
abraded with a scalpel blade and a coverslip is placed on the
abrasion. After 2 hours, the coverslip is removed and replaced by
another coverslip every 2 hours for 8 hours. The coverslip is then
stained to view WBC in the damaged skin. In Luisa’s case, no WBC
accumulated on the slips. All types of WBC, however, were present
in high numbers in her blood. Flow cytometric analysis revealed
that no CD18 or CD11a (components of LFA-1) was detected on the
cell surfaces. Luisa was successfully treated with a bone marrow
transplant using stem cells from her mother.

In some families with this deficiency, a milder phenotype is
observed when individuals express 10% of the normal CD18 levels. In
light of this, what do you think the effects would be to an
individual with normal levels of CD18 given monoclonal antibodies
against CD18? Can you think of a situation in which such a
treatment might be useful?