Question

4-1. As a third-year medical student working in the hospital, you are treating a young boy, Jacob, and a young girl, Kristen, who have had chronic ear infections by pyogenic bacteria. Blood work shows that they both have elevated levels of IgM.

(a) What two B cell deficiencies could explain these observations? (do not use abbreviations)

(b) Which patient is more likely (or less likely) to have one type of those deficiencies than the other type and why?

(c) How can you test to determine which of the two possible B cell deficiencies they might have?

(d) Of the two deficiencies named in (b), which one would cause susceptibility to opportunistic infections like Pneumocystis jiroveci and why?

Explain answers in through details.

Answer 1

B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system by secreting antibodies. These antibodies, which are specific to each pathogen and are able to lock onto the surface of an invading cell and mark it for destruction by other immune cells.

Ig are proteins secreted by or present on the surface of B-cells

The main functions of B cells are:

• to make antibodies against antigens,
• to perform the role of antigen-presenting cells (APCs),
• to develop into memory B cells after activation by antigen interaction.

Without B-cells, your body would not be as effective in fighting a number of common bacteria and viruses; and individual would lack the long-lasting "memory antibody" function that is typical after recovering from an infection or after being immunized against a specific infectious disease.

Pure B-cell immunodeficiencies include the following:

• X-linked agammaglobulinemia

• X-linked immunodeficiency with hyper-IgM

• Selective IgA deficiency

• Selective IgM deficiency

• IgG subclass deficiency

• Transient hypogammaglobulinemia of infancy

• Common variable immunodeficiency

• Kappa/lambda light-chain deficiency

• Immunodeficiency with thymoma

• IgE hypogammaglobulinemia

• Hypoxic-ischemic encephalopathy (HIE) syndrome

A history of recurrent infections is a common presenting feature in B cell deficiency . The onset of symptoms in childhood is suggestive of an inherited disorder.Patients with B-cell deficiencies begin having bacterial infections at 7-9 months of age, when the placental antibodies fall to undetectable levels. Acquired B-cell disorders may start in persons of any age, depending on the underlying cause.

Types of B Cell deficiency disorder

• X-linked agammaglobulinemia

• The disorder affects boys only and is characterized by recurrent pyogenic infections during the second half of the first year of life. Sinopulmonary infections are the most common (60% of patients), with chronic otitis media, sinusitis, and pneumonia. The other common infections, in decreasing order, are gastroenteritis (35%), pyoderma (25%), arthritis (20%), and meningitis/encephalitis (16%). Septicemia (10%), conjunctivitis (8%), and osteomyelitis (3%) are less common.

• The susceptibility to P carinii and C parvum, both opportunistic infections controlled by cellular immunity, may be explained by the nature of the defect underlying this disease.

• Common variable immunodeficiency

• Common variable immunodeficiency (CVID) is the most common cause of hypogammaglobulinemia and affects both sexes equally.Recurrent upper and lower respiratory infections, such as otitis media, sinusitis, pneumonia, and bronchitis, are the most common symptoms. Arthralgia and conjunctivitis are frequently reported. Pyoderma, urinary tract infection, osteomyelitis/arthritis, and meningitis/encephalitis are less common

Tests used to help diagnose an immunodeficiency disorder may include:

• Complement levels in the blood, or other tests to measure substances released by the immune system.

• HIV test.
• Immunoglobulin levels in the blood.
• Protein electrophoresis (blood or urine)
• T (thymus derived) lymphocyte count.
• White blood cell count.