2.4.1 Diseases of B Cell Deficiency

Question 1

In which of the following age groups might you begin to suspect a B cell deficiency?

0-4 months

1-3 years

12-15 years

20-30 years

50-60 years

Answer 1

1-3 years

Question 2

Which of the following classes of microorganisms would you expect to be most problematic in a patient with a B cell deficiency?

Extracellular bacteria

Fungi

Intracellular bacteria

Helminths

Viruses

Answer 2

Extracellular bacteria. If you thought helminths, you wouldn’t be very far off b/c helminth reactions are mediated by IgE. However, helminths are not as prevalent in this area of the world.

Question 3

What is causing the abnormality in this CXR of this 2 y/o?

Answer 3

“In younger children, bacterial pneumonia frequently has a very round, well-defined appearance on chest radiography, simulating a mass (Fig. C3.2). This is referred to as round pneumonia and is most common in children younger than 8 years of age. Round pneumonia is more common in the lower lobes and is most often caused by Streptococcus pneumoniae infection. The reason for this appearance in children is thought to be due to underdevelopment of collateral pathways of air circulation. In the appropriate clinical setting in a child with cough and fever, a lung mass seen on chest radiograph should be considered to be round pneumonia, and additional imaging with CT is not indicated. Follow-up radiographs should be obtained several weeks after appropriate antibiotic therapy to ensure resolution. After 8 years of age, however, if a round mass is seen on chest radiograph, other pathology should be considered.” - Chapter 9: Pediatric Radiology

Question 4

36 year-old African American man presents to you clinic with general fatigue and a fever (39.5℃). He reminds you that his spleen was removed as a child because of sickle cell disease. Blood cultures grew Pneumococcus. Which of the following immune parameters are MOST likely to be impaired in this patient?

A.BCR editing

B.Pneumococcus-specific IgG2

C. Pneumococcus-specific CD8+ T cells

D. Serum IFNγ

E. Thymic selection

Answer 4

Pneumococcus-specific IgG2

Question 5

If there was a mutation in the BCR signaling pathway, where would you expect the B Cell to arrest in development?

Answer 5

The Pre-B Cell Stage. Once the heavy chain is rearranged and paired with a pre-light chains on the B cell surface, it will not be able to signal back to cell signifying that it was able to successfully rearrange its heavy chain.

Question 6

A patient presenting with petechial hemorrhages in the palpebral conjunctivae is suggestive of what?

Answer 6

Bursting of BVs as a result of intrinsic clotting (DIC)

Question 7

What is the main lymphoid organ used to fight blood borne pneumococcal infections?

Answer 7

The spleen. It has the macrophages in its marginal zone which helps hold the pneumococcus down while a B cell response is developed.

Question 8

What would you expect to see in the differentiating lab testing of these B cell deficiencies: XLA, Hyper-IgM, Asplenia, Ig Deficiency, CVID?

Answer 8

XLA: Absense of B cells

Hyper-IgM: norm/high IgM, low IgG/A, norm B cell numbers

Asplenia: Ultrasound Howell-Jolly bodies

Ig Deficiency: decreased select Ig

CVID: decreased IgG and decreased IgM and/or IgA

Question 9

What is a Howell-Jolly body? What dz is known for its presence of Howell-Jolly bodies?

Answer 9

Very small spherical nuclear remnant in a RBC.

Asplenia

Question 10

What are the two types of Hyper-IgM? Which branch of the adaptive immune system is responsible for each?

Answer 10

Type I: T Cell

Type II: B Cell (lack of activation-induced cytosine deaminase)

Question 11

What are some of the common features of XLA, Hyper-IgM, and asplenia?

Answer 11

infections begin before transient hypogammaglobulinemia

extracellular pathogens (typically sinusitis/bronchitis/otitis/pneumonia)