Q.1 What is the main function of the T cell receptor (TCR)?
To recognize antigens presented by MHC molecules
To secrete antibodies
To present antigens to B cells
To phagocytose pathogens
Explanation - TCRs are specialized proteins on T cells that recognize peptide antigens bound to MHC molecules on antigen-presenting cells.
Correct answer is: To recognize antigens presented by MHC molecules
Q.2 Which chains make up the majority of a conventional TCR?
Alpha and beta chains
Gamma and delta chains
Mu and lambda chains
Kappa and lambda chains
Explanation - Most T cells express alpha-beta TCRs, while a minority express gamma-delta TCRs.
Correct answer is: Alpha and beta chains
Q.3 Which molecule provides the primary signal for T cell activation?
CD3 complex
MHC-peptide binding to TCR
CD28-B7 interaction
IL-2 secretion
Explanation - Signal 1 in T cell activation comes from the binding of the TCR to the peptide-MHC complex.
Correct answer is: MHC-peptide binding to TCR
Q.4 Which co-receptor is expressed on cytotoxic T cells and helps in MHC class I recognition?
CD8
CD4
CD28
CD40
Explanation - CD8 is a co-receptor that binds to MHC class I molecules, aiding cytotoxic T cell recognition.
Correct answer is: CD8
Q.5 What is the role of the CD3 complex in T cell signaling?
Transduces signals from the TCR into the cell
Binds antigen directly
Inhibits T cell activation
Activates B cells
Explanation - CD3 is associated with the TCR and contains ITAMs that initiate intracellular signaling upon antigen recognition.
Correct answer is: Transduces signals from the TCR into the cell
Q.6 Which signaling motif is found in the cytoplasmic tails of CD3 chains?
ITAM (Immunoreceptor Tyrosine-based Activation Motif)
SH2 domain
PH domain
Leucine zipper
Explanation - ITAMs in CD3 cytoplasmic tails are phosphorylated to propagate the activation signal.
Correct answer is: ITAM (Immunoreceptor Tyrosine-based Activation Motif)
Q.7 Which kinase is first recruited to phosphorylated ITAMs in T cell signaling?
ZAP-70
Lck
PKC
PI3K
Explanation - ZAP-70 binds to phosphorylated ITAMs and is crucial for downstream signaling events in T cells.
Correct answer is: ZAP-70
Q.8 Which co-stimulatory molecule interacts with CD28 on T cells?
B7 (CD80/CD86)
MHC I
MHC II
ICAM-1
Explanation - Co-stimulation via CD28-B7 interaction is required for full T cell activation and IL-2 production.
Correct answer is: B7 (CD80/CD86)
Q.9 Which transcription factor is activated by calcium signaling in T cells?
NFAT
NF-κB
AP-1
STAT3
Explanation - Calcium influx activates the phosphatase calcineurin, which dephosphorylates NFAT, allowing it to enter the nucleus.
Correct answer is: NFAT
Q.10 Which adaptor protein links TCR engagement to Ras-MAPK pathway activation?
LAT
ZAP-70
CD3
CD28
Explanation - LAT (Linker for Activation of T cells) organizes signaling molecules and links TCR engagement to multiple downstream pathways.
Correct answer is: LAT
Q.11 Which T cell subset primarily expresses CD4 and recognizes MHC class II?
Helper T cells
Cytotoxic T cells
Regulatory T cells
Gamma-delta T cells
Explanation - CD4+ T cells recognize peptides presented by MHC class II molecules on antigen-presenting cells.
Correct answer is: Helper T cells
Q.12 Which signaling molecule is critical for TCR-induced actin cytoskeleton rearrangement?
Vav
ZAP-70
CD3
NFAT
Explanation - Vav is a guanine nucleotide exchange factor that activates Rho family GTPases, regulating actin cytoskeleton dynamics.
Correct answer is: Vav
Q.13 Which cytokine is primarily produced upon T cell activation and drives T cell proliferation?
IL-2
IL-4
IL-10
IFN-γ
Explanation - IL-2 is secreted by activated T cells and acts in an autocrine manner to promote clonal expansion.
Correct answer is: IL-2
Q.14 Which signaling pathway is activated by DAG and calcium in T cells?
PKC/NF-κB pathway
Ras-MAPK pathway
JAK-STAT pathway
PI3K-Akt pathway
Explanation - DAG activates PKC, which leads to NF-κB activation, an essential pathway for T cell activation.
Correct answer is: PKC/NF-κB pathway
Q.15 Which receptor-ligand pair is inhibitory for T cell activation?
CTLA-4 and B7
CD28 and B7
CD4 and MHC II
CD8 and MHC I
Explanation - CTLA-4 competes with CD28 for B7 binding and delivers inhibitory signals to dampen T cell responses.
Correct answer is: CTLA-4 and B7
Q.16 What is the role of Lck in TCR signaling?
Phosphorylates ITAMs on CD3 chains
Activates NFAT
Recruits ZAP-70
Stimulates IL-2 secretion directly
Explanation - Lck, a Src family kinase, phosphorylates ITAMs on CD3 chains, allowing ZAP-70 recruitment.
Correct answer is: Phosphorylates ITAMs on CD3 chains
Q.17 Which TCR signaling adaptor recruits PLC-γ1 to the membrane?
LAT
Vav
Grb2
CD28
Explanation - LAT forms a signalosome that recruits PLC-γ1, leading to calcium mobilization and DAG production.
Correct answer is: LAT
Q.18 Which lipid second messenger is produced by PLC-γ1 activation in T cells?
IP3 and DAG
cAMP
PIP2
Phosphatidylserine
Explanation - PLC-γ1 hydrolyzes PIP2 into IP3, which increases calcium, and DAG, which activates PKC.
Correct answer is: IP3 and DAG
Q.19 Which transcription factor is activated downstream of the Ras-MAPK pathway in T cells?
AP-1
NFAT
NF-κB
STAT1
Explanation - The Ras-MAPK pathway leads to the activation of AP-1, a transcription factor important for cytokine gene expression.
Correct answer is: AP-1
Q.20 Which kinase phosphorylates LAT after ZAP-70 activation?
ZAP-70 itself
Lck
PKC
PI3K
Explanation - After being recruited to phosphorylated ITAMs, ZAP-70 phosphorylates LAT to propagate downstream signaling.
Correct answer is: ZAP-70 itself
Q.21 Which molecule provides the survival signal during T cell activation?
IL-2
IL-4
IL-6
TNF-α
Explanation - IL-2 promotes T cell survival, proliferation, and differentiation after activation.
Correct answer is: IL-2
Q.22 Which molecule is critical for TCR-induced PI3K activation?
CD28
CD3
ZAP-70
LAT
Explanation - CD28 co-stimulation recruits PI3K, leading to Akt activation and enhanced T cell survival and metabolism.
Correct answer is: CD28
Q.23 Which TCR subset is involved in mucosal immunity and can recognize antigens without MHC?
Gamma-delta T cells
Alpha-beta T cells
CD4+ T cells
CD8+ T cells
Explanation - Gamma-delta T cells often reside in mucosal tissues and can recognize non-peptide antigens in an MHC-independent manner.
Correct answer is: Gamma-delta T cells
Q.24 Which adaptor links TCR signaling to NF-κB activation?
CARMA1
LAT
Vav
ZAP-70
Explanation - CARMA1 is part of the CBM complex that activates NF-κB downstream of TCR engagement.
Correct answer is: CARMA1