A 32-year-old Caucasian male is brought to the emergency room for recurrent diarrhea. He has had multiple upper respiratory infections since birth and does not take any medications at home. It is determined that Giardia lamblia is responsible for the recurrent diarrhea. The physician performs a serum analysis and finds normal levels of mature B lymphocytes. What other finding on serum analysis predisposes the patient to recurrent diarrheal infections?
1.Deficiency in CD8+ T cells
2.Deficiency in neutrophils
3.Deficiency in IgA
4.Deficiency in NK cells
5.Deficiency in IgG
sol:
The patient has common variable immunodeficiency disorder (CVID), which leads hypoagammaglobulinemia. Specifically, the patient has a deficiency in IgA, therefore he has an increased susceptibility to Giardia infection.
IgA plays an important role in mucosal immunity. By its presence on the surface of intestinal mucosal cells, IgA is able to prevent the binding of pathogens to the epithelial cells; thus, preventing protozoa like Giardia lamblia from causing inflammation. Its absence, therefore, leads to the increased likelihood of repeat infection of the GI mucosa and repeat episodes of non-bloody diarrhea.
Illustration A shows a light microscopic view of Giardia lamblia.