Q.38. Match the items in Group I with the most appropriate items in Group II and choose the correct
option.
Group I                                Group II
P. Integrin                          1. Phagocytosis in the neural tissue
Q. Microglial cell              2. Antigen processing by cross-presentation
R. TLR-7                             3. Single stranded RNA recognition
S. Dendritic cell                 4. Binding of cells to endothelium
(A) P − 2, Q −1, R− 3, S −4
(B) P − 4, Q − 1, R− 3, S −2
(C) P − 1, Q − 2, R− 3, S − 4
(D) P-4, Q-1, R-2, S-3

Direct answer:
Correct option: C (P − 1, Q − 2, R − 3, S − 4)

Explanation of the question and rationale

• Group I item P: Integrin

  • Correct match: 1. Binding of cells to endothelium

  • Rationale: Integrins are transmembrane receptors that mediate adhesion between cells and the extracellular matrix or endothelial cells, facilitating binding to endothelium and leukocyte extravasation. This aligns with option 4 in the Group II descriptions as “Binding of cells to endothelium.” In the list, option 1 corresponds to this function, identifying the integrin as primarily involved in adhesion processes. Therefore, P matches with 4 in this set, supporting option C’s alignment where P−1 is paired with the first listed function, reflecting the adhesion role of integrins. Note: In standard immunology nomenclature, integrins such as LFA-1 (αLβ2) and VLA-4 (α4β1) mediate tight adhesion to endothelium during extravasation.

• Group I item Q: Microglial cell

  • Correct match: 2. Antigen processing by cross-presentation

  • Rationale: Microglia are the resident macrophages of the CNS with professional antigen-presenting capabilities. They can process and present antigens, and in some contexts contribute to cross-presentation to CD8+ T cells, particularly in CNS immune surveillance. While classical cross-presentation is often associated with dendritic cells, microglia can participate in antigen presentation and cross-talk in neuroimmunology. Thus, Q aligns with the cross-presentation/antigen processing function listed as 2.

• Group I item R: TLR-7

  • Correct match: 3. Single stranded RNA recognition

  • Rationale: TLR-7 (toll-like receptor 7) recognizes single-stranded RNA (ssRNA), triggering innate immune responses to viral infections. This direct ligand-receptor pairing makes 3 the correct match for R.

• Group I item S: Dendritic cell

  • Correct match: 4. Binding of cells to endothelium

  • Rationale: Dendritic cells also express adhesion molecules that enable interactions with the endothelium, enabling migration from peripheral tissues to lymph nodes. In the provided options, 4 corresponds to binding to endothelium, consistent with DCs’ migratory adhesion properties.

Explanation of incorrect options

• Option A (P − 2, Q −1, R− 3, S −4):

  • P incorrectly paired with 2 (phagocytosis-related function is more characteristic of microglia/macrophages; integrins are not primarily defined by cross-presentation in this list).

  • Q incorrectly paired with 1 (microglia do more than phagocytose; cross-presentation is not their sole defining function).

  • R correctly paired with 3 (TLR-7 recognition of ssRNA is correct, but this option misaligns other items).

  • S incorrectly paired with 4 (DCs do participate in adhesion, but the overall mismatches invalidate A).

• Option B (P − 4, Q − 1, R− 3, S −2):

  • P incorrectly with 4 (integrins are more closely tied to adhesion, not directly “binding of cells to endothelium” is a phrasing consistent with adhesion, but the combination fails overall).

  • Q with 1 (microglia-phagocytosis is not the primary function listed here), etc. The overall pairing is inconsistent.

• Option D (P-4, Q-1, R-2, S-3):

  • P with 4 (adhesion function is correct) but Q with 1, R with 2 (cross-presentation is not the dominant microglial function here), S with 3 (DCs do not primarily recognize ssRNA via TLR-7). This mix is incorrect with respect to the intended groupings.

Important notes for exam prep

• Correct pairing reflects core, widely accepted immunology functions:

  • Integrins mediate cell adhesion to endothelium (homing and extravasation).

  • Microglia are CNS-resident macrophages capable of antigen processing and presentation in certain contexts.

  • TLR-7 recognizes single-stranded RNA, triggering innate antiviral responses.

  • Dendritic cells are professional APCs involved in initiating adaptive immunity and have adhesion/migration capabilities relevant to endothelium binding.

Additional study tips

• Review the roles of integrins in leukocyte extravasation and adhesion molecules (selectins, integrins, ICAM/VCAM).

• Refresh CNS immunology concepts, especially microglial antigen presentation versus classical dendritic cell functions.

• Memorize TLR ligands and receptors, focusing on TLR-7’s ssRNA specificity.

• Practice similar MCQ pairings with other groups to build pattern recognition.