Immunology: common variable immunodeficiency: practice question

A Microbiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Microbiology · Immunology: common variable immunodeficiency

Sample item

A 28-year-old man has had recurrent sinusitis and pneumonia since age 22 and now has chronic diarrhoea with Giardia in the stool. Serum IgG, IgA and IgM are all low, antibody response to vaccines is absent and non-caseating granulomas are found in the lung. Flow cytometry is most likely to show which pattern, distinguishing this disorder from X-linked agammaglobulinaemia?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Near-normal CD19-positive B cells that fail to differentiate into plasma cells

Common variable immunodeficiency usually presents in the second to fourth decade with hypogammaglobulinaemia, poor vaccine responses, giardiasis, autoimmunity and granulomatous disease. B cells are present in normal or slightly reduced numbers but do not mature into antibody-secreting plasma cells. In X-linked agammaglobulinaemia, B cells are almost absent and presentation is in infancy.

Option by option

  • A. Absent CD19-positive B cells with a BTK gene mutation

    Absent B cells from a BTK mutation describe X-linked agammaglobulinaemia, which presents in a boy in infancy.

  • B. Normal B cells with absent CD40 ligand on activated T cells

    CD40 ligand deficiency causes hyper IgM syndrome, in which IgM is raised rather than low.

  • C. Absent CD3-positive T cells with adenosine deaminase deficiency

    Absent T cells with ADA deficiency describe a form of severe combined immunodeficiency presenting in the first months of life.

  • D. Near-normal CD19-positive B cells that fail to differentiate into plasma cells (correct)

    Near-normal numbers of B cells that cannot become plasma cells fit the adult onset, low immunoglobulins of all classes and granulomas.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Near-normal CD19-positive B cells that fail to differentiate into plasma cells. Common variable immunodeficiency usually presents in the second to fourth decade with hypogammaglobulinaemia, poor vaccine responses, giardiasis, autoimmunity and granulomatous disease.

Why is "Absent CD19-positive B cells with a BTK gene mutation" not the answer?

Absent B cells from a BTK mutation describe X-linked agammaglobulinaemia, which presents in a boy in infancy.

Why is "Normal B cells with absent CD40 ligand on activated T cells" not the answer?

CD40 ligand deficiency causes hyper IgM syndrome, in which IgM is raised rather than low.

Why is "Absent CD3-positive T cells with adenosine deaminase deficiency" not the answer?

Absent T cells with ADA deficiency describe a form of severe combined immunodeficiency presenting in the first months of life.

What concept does this question test?

It tests Immunology: common variable immunodeficiency in Microbiology. B cells are present in normal or slightly reduced numbers but do not mature into antibody-secreting plasma cells. In X-linked agammaglobulinaemia, B cells are almost absent and presentation is in infancy.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Immunology: common variable immunodeficiency?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.