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GATE 2023 BT Q.17: solution and answer

GATE 2023 · BTQ.17 · 1 mark · MCQ

Dendritic cells are involved in cross-presentation of antigens. Which of the following protein(s) is(are) required for cross-presentation?
P. Basic leucine zipper ATF-like transcription factor 3 (BATF3)
Q. Membrane associated ring-CH-type finger 1 (MARCH-1)
R. Solute carrier family 10 member 1 (SLC10A1)
S. Class II-associated invariant chain peptide (CLIP)

  1. (A)

    P only

  2. (B)

    P and R only

  3. (C)

    P, Q and R only

  4. (D)

    S only

See the question in the paper
GATE 2023 BT question 17Tap to open full size

Answer and solution

ANSWER

The answer is (A): only BATF3 (P) is required for cross-presentation.

Official answer: ASource: Official answer key, GATE 2023 BT (IIT Kanpur)

  1. Cross-presentation loads antigen taken up from outside the cell onto MHC class I, so that CD8 T cells are primed. In mice it is done mainly by the cDC1 subset of dendritic cells (CD8α+ and CD103+).

  2. P, BATF3: this transcription factor is needed for cDC1 development. Batf3-deficient mice lack cDC1 cells and cross-present very poorly. So P is required.

  3. Q, MARCH-1: this E3 ubiquitin ligase ubiquitinates MHC class II and CD86 and controls how long they stay on the cell surface. It acts on the MHC II pathway, not on cross-presentation. So Q is not required.

  4. R, SLC10A1: this is the sodium taurocholate cotransporting polypeptide, a bile-acid transporter of hepatocytes that is also the hepatitis B virus entry receptor. It has no role in antigen processing. So R is not required.

  5. S, CLIP: this is a fragment of the invariant chain that sits in the MHC II peptide groove until HLA-DM swaps it for an antigenic peptide. It belongs to MHC II loading, not to cross-presentation. So S is not required.

  6. Only P is required, so the answer is (A) P only.

KEY IDEA

Cross-presentation depends on cDC1 dendritic cells, whose development needs BATF3. MARCH-1 and CLIP belong to the MHC II pathway. SLC10A1 is a liver bile-acid transporter.

WATCH OUT FOR

Picking MARCH-1 or CLIP because they sound like antigen-presentation proteins. Both act on MHC II, not on the MHC I route used in cross-presentation. SLC10A1 is also chosen by mistake because it is an unfamiliar name.

From the GATE 2023 BT paper. Every question of this paper · Download the full paper · All 7 Adaptive immunity questions, with notes

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