Q.1 What is immunological tolerance?
The ability of immune cells to destroy pathogens
A state of unresponsiveness to specific antigens
Overproduction of antibodies against all antigens
Enhanced immune reaction to foreign particles
Explanation - Immunological tolerance is the process where the immune system does not mount a response against certain antigens, typically self-antigens, preventing autoimmunity.
Correct answer is: A state of unresponsiveness to specific antigens
Q.2 Which mechanism primarily prevents autoimmunity?
Central tolerance
Complement activation
Phagocytosis
Antigen presentation
Explanation - Central tolerance occurs in the thymus and bone marrow, where self-reactive lymphocytes are eliminated or inactivated, preventing autoimmunity.
Correct answer is: Central tolerance
Q.3 Where does central tolerance of T cells occur?
Spleen
Thymus
Lymph nodes
Bone marrow
Explanation - Developing T cells undergo selection in the thymus, where self-reactive ones are deleted through negative selection.
Correct answer is: Thymus
Q.4 Which process eliminates B cells that strongly recognize self-antigens during development?
Clonal expansion
Clonal deletion
Complement fixation
Somatic hypermutation
Explanation - Clonal deletion removes self-reactive lymphocytes during their development, thus ensuring self-tolerance.
Correct answer is: Clonal deletion
Q.5 What is peripheral tolerance?
Tolerance induced outside primary lymphoid organs
Tolerance induced only in the thymus
Innate immune system tolerance
Enhanced immune reactivity
Explanation - Peripheral tolerance mechanisms (e.g., anergy, suppression) act outside the thymus or bone marrow to prevent autoimmune responses.
Correct answer is: Tolerance induced outside primary lymphoid organs
Q.6 Which cells are most critical for maintaining peripheral tolerance?
Cytotoxic T cells
Regulatory T cells
B cells
Natural killer cells
Explanation - Regulatory T cells (Tregs) suppress immune responses and maintain tolerance to self-antigens.
Correct answer is: Regulatory T cells
Q.7 What is anergy in immunology?
Increased immune reactivity
State of non-responsiveness of lymphocytes to antigen
Apoptosis of immune cells
Overproduction of antibodies
Explanation - Anergy refers to functional inactivation of lymphocytes when they encounter antigen without proper co-stimulation.
Correct answer is: State of non-responsiveness of lymphocytes to antigen
Q.8 Which molecule is essential for inducing T cell anergy when absent?
CD28
CD3
CD40
CD19
Explanation - CD28 provides co-stimulatory signals to T cells; absence of co-stimulation leads to anergy.
Correct answer is: CD28
Q.9 What happens to T cells that strongly recognize self-antigen in the thymus?
They differentiate into memory T cells
They undergo apoptosis
They migrate to the spleen
They become B cells
Explanation - Negative selection eliminates autoreactive T cells by apoptosis in the thymus.
Correct answer is: They undergo apoptosis
Q.10 Which transcription factor is critical for the development of regulatory T cells?
NF-κB
FoxP3
STAT3
p53
Explanation - FoxP3 is the key transcription factor required for Treg differentiation and function.
Correct answer is: FoxP3
Q.11 Tolerance to dietary antigens is an example of:
Central tolerance
Peripheral tolerance
Innate tolerance
Allergic tolerance
Explanation - Tolerance to harmless external antigens like food proteins is achieved via peripheral tolerance mechanisms, mainly in the gut.
Correct answer is: Peripheral tolerance
Q.12 Which condition results from breakdown of self-tolerance?
Autoimmunity
Immunodeficiency
Allergy
Transplant rejection
Explanation - Failure of tolerance mechanisms leads to immune attack on self-antigens, causing autoimmune diseases.
Correct answer is: Autoimmunity
Q.13 What is clonal ignorance?
Complete removal of self-reactive clones
Self-reactive lymphocytes ignoring antigens due to low exposure
Overactivation of lymphocytes
Failure of antibody production
Explanation - In clonal ignorance, self-reactive lymphocytes persist but do not cause disease because self-antigen concentration is too low.
Correct answer is: Self-reactive lymphocytes ignoring antigens due to low exposure
Q.14 Which cytokine is most associated with regulatory T cell function?
IL-10
IL-2
IL-4
IL-12
Explanation - Regulatory T cells secrete IL-10 and TGF-β to suppress immune responses.
Correct answer is: IL-10
Q.15 The induction of tolerance to a transplanted organ is called:
Autoimmunity
Allograft tolerance
Anergy
Immune privilege
Explanation - When the immune system accepts transplanted tissue without rejection, it is referred to as allograft tolerance.
Correct answer is: Allograft tolerance
Q.16 What is immune privilege?
Ability of some sites to avoid immune responses
Permanent suppression of immunity
Failure of immune cell migration
Overactivation of immune responses
Explanation - Immune privileged sites (like eye, brain, testes) naturally avoid strong immune responses to protect tissue function.
Correct answer is: Ability of some sites to avoid immune responses
Q.17 What is the fate of autoreactive B cells in the bone marrow?
They become plasma cells
They are deleted or edited
They migrate to the thymus
They secrete IgE
Explanation - Autoreactive B cells undergo clonal deletion or receptor editing in the bone marrow.
Correct answer is: They are deleted or edited
Q.18 What is receptor editing in B cells?
Switching of heavy chain genes
Rearrangement of light chain genes to reduce self-reactivity
Activation of T cell receptors
Overproduction of antibodies
Explanation - B cells can edit their receptors by rearranging light chain genes to reduce self-reactivity.
Correct answer is: Rearrangement of light chain genes to reduce self-reactivity
Q.19 Which checkpoint ensures T cells with low affinity for self-MHC survive?
Positive selection
Negative selection
Peripheral tolerance
Immune privilege
Explanation - Positive selection in the thymus allows T cells that can moderately bind self-MHC to survive.
Correct answer is: Positive selection
Q.20 Which checkpoint eliminates high-affinity self-reactive T cells?
Positive selection
Negative selection
Somatic hypermutation
Clonal expansion
Explanation - Negative selection deletes T cells that bind strongly to self-antigens, preventing autoimmunity.
Correct answer is: Negative selection
Q.21 What is oral tolerance?
Tolerance induced by gut exposure to antigens
Tolerance to respiratory allergens
Tolerance to intravenous antigens
Tolerance to self-antigens only
Explanation - Oral tolerance is a form of peripheral tolerance induced when antigens are introduced via the gastrointestinal tract.
Correct answer is: Tolerance induced by gut exposure to antigens
Q.22 Which of the following is NOT an immune privileged site?
Eye
Brain
Skin
Testes
Explanation - Skin mounts active immune responses; immune privilege is seen in organs like the eye, brain, and testes.
Correct answer is: Skin
Q.23 Breakdown of peripheral tolerance may result in:
Immunodeficiency
Autoimmune diseases
Graft tolerance
Allergic tolerance
Explanation - Failure of peripheral tolerance mechanisms can lead to diseases such as lupus or rheumatoid arthritis.
Correct answer is: Autoimmune diseases
Q.24 Which signal is necessary for full T cell activation and prevents anergy?
Signal from MHC-TCR only
Signal from co-stimulatory molecules
Signal from antibodies
Signal from complement proteins
Explanation - T cells require antigen recognition (signal 1) and co-stimulatory signals (signal 2) for activation; absence of signal 2 leads to anergy.
Correct answer is: Signal from co-stimulatory molecules
Q.25 Immune tolerance in pregnancy is largely mediated by:
Maternal cytotoxic T cells
Maternal Tregs and cytokines
Maternal NK cell destruction
Fetal autoantibodies
Explanation - Regulatory T cells and immunosuppressive cytokines prevent maternal immune attack on the fetus.
Correct answer is: Maternal Tregs and cytokines