Immunology: immunofluorescence: 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.

Try it

Microbiology · Immunology: immunofluorescence

Sample item

In the fluorescent treponemal antibody absorption test for syphilis, a patient's serum is layered on a slide containing Treponema pallidum. In this indirect immunofluorescence technique, which reagent is labelled with fluorescein?

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

The answer and the reasoning

B. Antihuman immunoglobulin

In the indirect method, the patient's unlabelled antibody binds the antigen on the slide, and a fluorescein-labelled antihuman globulin is then added to detect it. This amplifies the signal. In the direct method, the specific antibody is labelled itself, as in rabies antigen detection.

Option by option

  • A. The patient's serum antibody itself

    The patient's serum antibody is not labelled and is the analyte being detected.

  • B. Antihuman immunoglobulin (correct)

    Correct. A labelled secondary antibody detects the patient's bound antibody.

  • C. The Treponema pallidum on the slide

    The antigen is unlabelled and is fixed on the slide.

  • D. Complement

    Complement is used in fixation tests, not in this method.

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.

More Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Antihuman immunoglobulin. In the indirect method, the patient's unlabelled antibody binds the antigen on the slide, and a fluorescein-labelled antihuman globulin is then added to detect it.

Why is "The patient's serum antibody itself" not the answer?

The patient's serum antibody is not labelled and is the analyte being detected.

Why is "The Treponema pallidum on the slide" not the answer?

The antigen is unlabelled and is fixed on the slide.

Why is "Complement" not the answer?

Complement is used in fixation tests, not in this method.

What concept does this question test?

It tests Immunology: immunofluorescence in Microbiology. This amplifies the signal. In the direct method, the specific antibody is labelled itself, as in rabies antigen detection.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: immunofluorescence?

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.