This set of Immunology Multiple Choice Questions & Answers (MCQs) focuses on “Cross Presentation of Exogenous Antigens and Presentation of Non-peptide Antigens”.
1. Which cells are principally involved in cross presentation of exogenous antigens?
a) Dendritic cells
b) Lymphocytes
c) B cells
d) Haematopoietic stem cells
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Explanation: Dendritic cells and some specialised subsets of dendritic cells are capable of performing cross presentation of exogenous antigens. They help these antigens to be presented on the MHC-1 molecules (Major Histocompatibility Complex-1). This cross presentation is quite necessary for maintaining the balance of the immune response and for fighting against virus or tumours.
2. Dendritic cells scan the central tissues for antigens to proceed cross-presentation.
a) True
b) False
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Explanation: Dendritic cells (DCs) need to scan the peripheral tissues for the antigens. This scanning mechanism is an initiation to the cross-presentation. Once the peripheral tissues are scanned and recognised, the antigens undergo internalization which in turn causes the DCs to get activated. The DCs further migrate towards the lymph nodes where they get the ability to induce adaptive immune responses.
3. Which cells can recognise the peptides that are loaded on MHC-1 molecules?
a) CD4+ helper T cells
b) CD4+ cytotoxic cells
c) CD8+ T cells
d) CD8+ T cells and CD4+ T cells
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Explanation: MHC molecules (1 & 2) work only when certain peptides are loaded on them. It is necessary for specific cells to recognise these peptides in order to carry out any immune activity. In the case of MHC-1 molecules, the peptides loaded are recognised by some antigen-specific CD8+ T cells. On the other hand, the peptides loaded on MHC-2 molecules are recognised by antigen-specific CD4+ helper T cells.
4. Which of the following is NOT a class of CD1-restricted lipid antigens?
a) Mycolic acids
b) Glycosylated mycolates
c) Phosphoglycolipids
d) Cathepsins
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Explanation: Mycolic acids, glycosylated mycolates and phosphoglycolipids like phosphatidylinositol mannosides (PIM) are some of the classes of CD1-restricted lipid antigens which have been identified till date. These antigens are composed of only lipids hence they are also termed as non-peptide antigens. These non-peptide antigens are expressed by T cells and their molecular structure can be studied by using chemical and mass spectrometric analysis.
5. In the case of MHC 2-restricted presentation, where do the antigens degrade?
a) Bone marrow
b) Endosomal compartments
c) Spleen
d) Endosomal/Lysosomal compartments
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Explanation: The cross-presentation of antigens on MHC-2 molecules is less understood as it leads to a completely different pathway of mechanism. However, the recent study shows that the antigens which get internalized are degraded to endosomal or lysosomal compartments with the help of certain proteases like cathepsins.
6. Which of the following receptor is NOT involved in cross-presentation of antigens?
a) T cell receptors
b) C-type lectin receptors
c) Chemokine receptors
d) Scavenger receptors
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Explanation: The initial step of cross-presentation involves some activities which are majorly carried out by receptors called as surface receptors. These receptors include C-type lectin receptors, immunoglobulin-gamma Fc region receptors, chemokine receptors and scavenger receptors. These receptors help in recognition and uptake of antigens in order to let them participate in the cross-presentation mechanism.
7. Which type of dendritic cells are considered to be perfect for cross-presentation?
a) cDC1
b) cDC2
c) pDCs
d) All subsets of dendritic cell
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Explanation: Dendritic cells (DCs) are divided into two major categories: conventional DCs (cDCs) and plasmacytoid DCs (pDCs). Conventional DCs are again further classified into cDC1 and cDC2. In vivo, in humans and mice, it is observed that cDC1 plays a very important role in the cross-presentation mechanism and hence this DC subset is considered to be potent and perfect for cross-presentation of antigens.
8. Which antigens bind to antigen-presenting cells for their presentation through mannose receptor?
a) Exogenous antigens
b) Lipoglycan antigens
c) Autoantigens
d) Lipopolysaccharide antigens
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Explanation: Lipoglycan antigens are the non-peptide antigens which bind to APCs (Antigen Presenting Cells) with the help of pattern recognition molecules like mannose receptor and CD14. They follow endosomal pathway which helps the lipoglycan antigens to bind to CD1. They further form antigen-CD1 complex where the actual recognition takes place.
9. Which of the following protease is known for its role in antigen degradation?
a) Arg-C
b) Cathepsin S
c) Trypsin
d) Cathepsin B
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Explanation: Cathepsin S is a lysosomal protease which plays a major role in antigen degradation. It is mainly known for its function in the vacuole pathway. It involves degradation of the proteins associated with antigens which may be unnecessary for further functions in order to carry out the presentation of MHC II molecules.
10. Non-peptide lipid antigens are presented to T cells by which of the following human proteins?
a) Human CD1 proteins
b) Human CD4 proteins
c) B-2 microglobulin
d) Glycosylated mycolates
View Answer
Explanation: A recent study has shown that there are a few non-peptide lipid antigens that are expressed and presented to T cells via human CD1 proteins. These proteins belong to the non-polymorphic family of glycoproteins and that one distinguishing feature about these proteins is that they are expressed outside the MHC molecules. CD1 proteins associate with b-2 microglobulin in order to express on the surface of APCs (Antigen-presenting cells).
Sanfoundry Global Education & Learning Series – Immunology.
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