Major Histocompatibility Complex Questions and Answers

Q: Which one of the following tissues/organs is least likely to experience graft rejection when transplanted from a person to an unrelated person?

The least likely to be rejected is the cornea.The cornea is avascular and has no lymphatic drainage, so donor antigens are poorly presented to the recipient's immune system, and the eye is an immune-privileged site. Corneal grafts between unrelated people therefore usually succeed without close tissue matching.Kidney and heart transplants are vascularised organs that need HLA matching and lifelong immunosuppression. Bone marrow needs close HLA matching too, and carries the added risk of graft-versus-host disease.

Q: Peptide-binding cleft in MHC-I is formed by

The peptide-binding cleft of MHC class I is formed by the \(\alpha 1\) and \(\alpha 2\) domains.The MHC I heavy chain has three extracellular domains. The \(\alpha 1\) and \(\alpha 2\) domains together build a platform of eight β-strands topped by two long α-helices, and the groove between the helices holds a peptide of about 8 to 10 residues for display to CD8+ T cells.The \(\alpha 3\) domain and the separate light chain \(\beta 2\)-microglobulin are immunoglobulin-like domains that sit beneath the platform and support it; \(\alpha 3\) is also where CD8 binds. Neither forms the cleft, so the options pairing \(\alpha 1\) or \(\alpha 2\) with \(\alpha 3\) or \(\beta 2\)-microglobulin are wrong. (In MHC II the cleft is built from \(\alpha 1\) and \(\beta 1\), one from each chain.)

Q: Transplantation of stem cell populations from genetically identical donor to the recipient is said to be :

The transplant is syngeneic.A syngeneic graft is one between genetically identical individuals, such as identical twins or animals of the same inbred strain. Because donor and recipient share the same tissue antigens, the graft is not rejected.An autologous graft (printed 'Autologus') uses the patient's own cells, an allogeneic graft comes from a genetically different member of the same species, and a xenogeneic graft comes from another species.

Q: Peptide antigen assemble with class 1 MHC aided by :

Assembly is aided by chaperone molecules.In the endoplasmic reticulum, newly made MHC class I heavy chains are held by the chaperones calnexin and then calreticulin, and with tapasin and ERp57 form the peptide-loading complex beside the TAP transporter. Only when a suitable peptide is loaded does the MHC molecule, with β2-microglobulin, leave for the cell surface.Immunoglobulins are antibodies, the T-cell receptor recognises the finished peptide-MHC complex at the cell surface, and cytokines are signalling molecules; none helps load the peptide.

Q: Peptide antigens assemble with class I MHC, aided by :

Peptides assemble with class I MHC aided by chaperone molecules.Class I heavy chains fold in the endoplasmic reticulum with the help of chaperones: calnexin first, then the peptide-loading complex of calreticulin, ERp57 and tapasin, which links the empty MHC molecule to the TAP transporter that brings cytosolic peptides into the ER. Once a peptide binds, the complex is released to the cell surface.Immunoglobulins and T cell receptors recognise antigen but play no part in loading class I molecules, and cytokines are secreted signalling proteins (interferon-gamma raises MHC expression but does not assemble the complex).

Which one of the following tissues/organs is least likely to experience graft rejection when transplanted from a person to an unrelated person?

A.bone marrow
B.cornea
C.heart
D.kidney

Exam Year(s)

GATE Life Sciences - 2024,

Answer: B

The least likely to be rejected is the cornea.

The cornea is avascular and has no lymphatic drainage, so donor antigens are poorly presented to the recipient's immune system, and the eye is an immune-privileged site. Corneal grafts between unrelated people therefore usually succeed without close tissue matching.

Kidney and heart transplants are vascularised organs that need HLA matching and lifelong immunosuppression. Bone marrow needs close HLA matching too, and carries the added risk of graft-versus-host disease.

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Peptide-binding cleft in MHC-I is formed by

A.\(\alpha 1\) and \(\alpha 2\) domains.
B.\(\alpha 1\) and \(\alpha 3\) domains.
C.\(\alpha 1\) domain and \(\beta 2\)-microglobulin.
D.\(\alpha 2\) domain and \(\beta 2\)-microglobulin.

Exam Year(s)

GATE Life Sciences - 2025,

Answer: A

The peptide-binding cleft of MHC class I is formed by the \(\alpha 1\) and \(\alpha 2\) domains.

The MHC I heavy chain has three extracellular domains. The \(\alpha 1\) and \(\alpha 2\) domains together build a platform of eight β-strands topped by two long α-helices, and the groove between the helices holds a peptide of about 8 to 10 residues for display to CD8⁺ T cells.

The \(\alpha 3\) domain and the separate light chain \(\beta 2\)-microglobulin are immunoglobulin-like domains that sit beneath the platform and support it; \(\alpha 3\) is also where CD8 binds. Neither forms the cleft, so the options pairing \(\alpha 1\) or \(\alpha 2\) with \(\alpha 3\) or \(\beta 2\)-microglobulin are wrong. (In MHC II the cleft is built from \(\alpha 1\) and \(\beta 1\), one from each chain.)

Discuss in Forum

Transplantation of stem cell populations from genetically identical donor to the recipient is said to be :

A.Autologus
B.Syngeneic
C.Allogeneic
D.Xenogeneic

Exam Year(s)

MH SET - 2019, MH SET - 2020, SET Exam - 2019, SET Exam - 2020,

Answer: B

The transplant is syngeneic.

A syngeneic graft is one between genetically identical individuals, such as identical twins or animals of the same inbred strain. Because donor and recipient share the same tissue antigens, the graft is not rejected.

An autologous graft (printed 'Autologus') uses the patient's own cells, an allogeneic graft comes from a genetically different member of the same species, and a xenogeneic graft comes from another species.

Discuss in Forum

Peptide antigen assemble with class 1 MHC aided by :

A.Chaperone molecules
B.Immunoglobulins
C.T-cell receptor
D.Cytokines

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

Assembly is aided by chaperone molecules.

In the endoplasmic reticulum, newly made MHC class I heavy chains are held by the chaperones calnexin and then calreticulin, and with tapasin and ERp57 form the peptide-loading complex beside the TAP transporter. Only when a suitable peptide is loaded does the MHC molecule, with β₂-microglobulin, leave for the cell surface.

Immunoglobulins are antibodies, the T-cell receptor recognises the finished peptide-MHC complex at the cell surface, and cytokines are signalling molecules; none helps load the peptide.

Discuss in Forum

Peptide antigens assemble with class I MHC, aided by :

A.Chaperone molecules
B.Immunoglobulins
C.T cell receptor
D.Cytokines

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: A

Peptides assemble with class I MHC aided by chaperone molecules.

Class I heavy chains fold in the endoplasmic reticulum with the help of chaperones: calnexin first, then the peptide-loading complex of calreticulin, ERp57 and tapasin, which links the empty MHC molecule to the TAP transporter that brings cytosolic peptides into the ER. Once a peptide binds, the complex is released to the cell surface.

Immunoglobulins and T cell receptors recognise antigen but play no part in loading class I molecules, and cytokines are secreted signalling proteins (interferon-gamma raises MHC expression but does not assemble the complex).

Discuss in Forum

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