Immunology: Hypersensitivity & Autoimmunity Quiz

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Questions and Answers

What role do Th1 CD4 cells play in Type IV hypersensitivity reactions?

They differentiate into B cells to produce immunoglobulins.

They directly kill infected cells.

They release antibodies to neutralize antigens.

They secrete cytokines that orchestrate the reaction. (correct)

What is a noted limitation of the Mantoux test for detecting Mycobacterium tuberculosis exposure?

It requires blood samples for accurate results.

It may also trigger a positive reaction in vaccinated individuals. (correct)

It can yield false negatives in previously infected individuals.

It is ineffective in young children.

Which neurotransmitter is primarily involved in activating macrophages during Type IV hypersensitivity?

IL-4

IL-10

IFN-γ (correct)

TNF-β

What is the primary mechanism through which certain haptens induce a strong T cell response?

They modify proteins, making them immunogenic. Signup and view all the answers

What is a common characteristic of drugs that cause specific hypersensitivity reactions related to HLA alleles?

They bind to MHC molecules and can modify peptide presentation. Signup and view all the answers

What are neoantigens?

Altered self peptides recognized as foreign Signup and view all the answers

What is the role of PD1 in cancer immunotherapy?

To deliver a negative signal to activated T cells Signup and view all the answers

Which types of cancer are more likely to respond to immunotherapy?

Cancers with more alterations recognized by T cells Signup and view all the answers

What is autoimmunity primarily characterized by?

Adverse immune responses against self-antigens Signup and view all the answers

How does autoimmunity typically arise?

Through a breakdown of self-tolerance Signup and view all the answers

Which condition represents chronic and debilitating autoimmune reactions?

Autoimmunity in 2-3% of individuals Signup and view all the answers

Which factor is associated with an increase in autoimmune conditions in developed countries?

Lack of early exposure to infections Signup and view all the answers

What happens to tissues affected by autoimmune disease?

They are infiltrated by lymphocytes without infection signs Signup and view all the answers

What modification does the A allele add to the core H antigen?

A terminal N-acetylgalactosamine Signup and view all the answers

In the ABO blood group system, which blood type corresponds to the unmodified H antigen?

Blood type O Signup and view all the answers

What is the primary risk associated with systemic anaphylaxis?

Extreme drop in blood pressure and anaphylactic shock Signup and view all the answers

Which blood type has the highest frequency in the European Caucasoid population?

Type O Signup and view all the answers

What immune response is triggered in an RhD-negative mother who carries an RhD-positive fetus?

Production of anti-RhD IgG antibodies Signup and view all the answers

Which treatment option is NOT typically used for systemic anaphylaxis?

Antibiotics to prevent infection Signup and view all the answers

What characterizes asthma with respect to inflammatory cells?

Presence of eosinophils, neutrophils, and basophils Signup and view all the answers

What role does RhoGam play in the management of Rh incompatibility?

Prevents the mother from reacting to her child's red blood cells Signup and view all the answers

During delivery, what happens to RhD-positive red blood cells from the fetus?

They leak into the maternal circulation Signup and view all the answers

What role does the T-Bet transcription factor play in asthma?

Drives T cells to differentiate into TH1 cells Signup and view all the answers

Which glycan is added by the B allele to the core H antigen?

Galactose Signup and view all the answers

How is an asthma response to an inhaled allergen initially measured?

Breathing exhalation rate after exposure Signup and view all the answers

What is the primary risk associated with an RhD-positive fetus in an RhD-negative mother during subsequent pregnancies?

Hemolytic disease of the newborn (HDNB) Signup and view all the answers

What leads to the late response in asthma after allergen exposure?

Release of leukotrienes and inflammatory mediators Signup and view all the answers

Which genetic factors are linked to asthma susceptibility?

TCR and TH1/TH2 balance related genes Signup and view all the answers

What happens if the antigen persists in asthma?

Chronic inflammation with TH2 cell recruitment occurs Signup and view all the answers

What is one potential mechanism of chronic rejection in transplanted organs?

Compromise of the blood supply leading to ischemia Signup and view all the answers

What role do B cells play in the context of chronic rejection?

They bind to shed donor HLA proteins with help from T cells. Signup and view all the answers

What is the significance of the H-Y antigen in organ transplants?

It can initiate rejection even between isogenic strains. Signup and view all the answers

Which type of transplant site is associated with minimal immune rejection?

Corneal transplants Signup and view all the answers

Which statement correctly reflects the role of HLA-matching in different transplant types?

HLA matching significantly influences allograft survival in haemopoietic stem cell transplants. Signup and view all the answers

Which type of hypersensitivity reaction is chronic rejection thought to be associated with?

Type III hypersensitivity involving IgG antibodies Signup and view all the answers

What is the primary mechanism by which macrophages contribute to tissue destruction?

By producing lytic enzymes Signup and view all the answers

What factor most significantly influences the success of kidney transplants with respect to HLA matching?

It is largely unnecessary due to strong immunosuppression. Signup and view all the answers

What does the precise relationship between the number of mis-matches and transplant survival indicate?

Fewer mis-matches generally improve survival rates. Signup and view all the answers

Which method has traditionally been used to determine HLA matching?

Microcytotoxicity testing Signup and view all the answers

What type of cells proliferate in the mixed lymphocyte reaction (MLR) as a result of MHC incompatibility?

Leukocytes Signup and view all the answers

Why did microcytotoxicity testing eventually get superseded by DNA typing in tissue typing laboratories?

It was less accurate. Signup and view all the answers

What is the key advantage of having a sibling or parent share one haplotype in haemopoietic transplants?

It can elicit a graft versus leukemia (GvL) response. Signup and view all the answers

What does the microcytotoxicity test help identify?

MHC incompatibilities Signup and view all the answers

Which of the following statements about HLA alleles is true?

Many HLA alleles make precise matching difficult. Signup and view all the answers

What percentage of cells typically respond to an allogeneic mismatch in vitro during MLR?

1% Signup and view all the answers

Study Notes

Immunological Tolerance

Tolerance is acquired, not hardwired.
The immune system is trained to recognise and respond to infectious non-self.
Adjuvants cue the immune system that an infection is occurring, converting soluble proteins into particulate material ingested by antigen-presenting cells (e.g., macrophages).
Complete Freund's Adjuvant (CFA) contains ground-up mycobacteria.
Tolerance is generally Central, occurring during lymphocyte development, or Peripheral, occurring after lymphocytes leave the primary organs.

Central Tolerance - T Cells

Clonal selection generates a diverse T cell repertoire, initially independent of specificity.
Positive selection selects clones with some affinity for MHC and self, and negative selection deletes clones binding strongly to self MHC plus peptide in the thymus.

Tolerance and Factors Affecting it

Tolerance is influenced by antigen timing, dose, costimulation, and location.
A celebrated experiment: Mice of strain A injected at birth with bone marrow from strain B, six weeks later grafted with skin from mouse B. The skin graft from mouse B was accepted, whereas a graft from mouse C was rejected.

Central Tolerance - B Cells

Theoretically, B cells require T cell help and shouldn't need tolerance.
B cells that react to abundant self-antigens are eliminated during their development.
Receptor editing allows self-reactive B cells to avoid apoptosis.

Five Mechanisms of T Cell Tolerance

Ignorance: Potential self-reactive T cells remain unactivated if antigens are hidden from the immune system.
Anergy: Occurs when TCR engagement occurs without the second signal, leading to non-responsiveness
Treg suppression(Regulatory T Cells): Suppress certain autoreactive T cells through mechanisms such as suppression of proliferation of naive T cells.
T cell exhaustion: A possible pathological phenomenon occurs when T cells fail to clear a chronic infection or tumour.

Immunologically Privileged Sites

The brain, eye, and testes have limited or no lymphatic drainage.
Tolerance can be broken If an organ is damaged or exposed to immune system.
Pregnancy has an immunologically-privileged site, the placenta. Tolerance mechanisms involve a physical barrier to maternal T cells, the lack of MHC class I on trophoblast cells, and the production of immunosuppressive factors such as alpha-fetoprotein and IDO.

Split Tolerance

Immune system components including T cells and B cells may not need to be tolerised as frequently as in other instances.
T cell tolerance may have been established but some autoreactive B cells remain.
It suggests that the immune response depends on different aspects (T cells versus B cells) that may be regulated to some degree independently.

Anergy

Anergy is a state of nonresponsiveness that can be induced in T cells and B cells.
It is triggered when the receptor is engaged with MHC molecules in the absence of the secondary signal, without cell death but with biochemical changes.

Dendritic Cells and Immune Activation

Dendritic cells are important antigen-presenting cells.
PAMPs or other stimulation induce the expression of high levels of the CD80 and CD86 costimulatory molecules.
Cells without this stimulation induce tolerance instead of activation.

Regulatory T Cells - Treg Suppression

Tregs are a special type of regulatory CD4 T cells.
Tregs express high levels of IL2-receptor CD25 and the FOXP3 transcription factor.
Development of Tregs is influenced by cytokine profile, chronic low-dose exposure to antigen, and antigen presentation by immature dendritic cells.

T Cell Exhaustion

T cell exhaustion is a possible pathological phenomenon of prolonged T cell responses to chronic infection or tumors.
It is characterized by expression of co-receptor PD1.
These cells are usually less responsive to stimulation with antigen.

Experimental Tolerance

A procedure that established tolerance to foreign antigens that normally result in an immune response.
Two examples of promising approaches are costimulatory receptor blockade (Abetacept) and cancer treatments that exploit and enhance immune responses to tumors (e.g., antibodies against CTLA4 or PD1)

Autoimmunity

Autoimmunity is an adverse immune response against self-antigens, where the immune system attacks host components resulting in a pathological change.
Many times the attack is short-lived and self-resolving following an infection. More serious cases (2-3% of people) can be chronic/life-threatening with major immunopathology.
Several factors contribute, possibly including early exposure to less frequent infections and a microbiome that is not as diverse in individuals whose immune systems do not encounter frequent infections.

Mechanisms of Autoimmune Pathology

Direct antibody-mediated effects: Antibodies binding to cells or tissues, leading to destruction or dysfunction.
Immune complex-mediated effects: IgG complexes deposited in tissues activate complement, resulting in inflammation.
T cell-mediated effects: CD8 T cells causing cytotoxicity or CD4 T cells activating macrophages damaging tissues.

Hypersensitivity

Hypersensitivity is a damaging immune response rather than beneficial response to a foreign or innocuous antigen.
Four main types of hypersensitivity: I, II, III, and IV. Type I: Immediate hypersensitivity (e.g., allergies) Type II: Antibody-mediated (e.g., blood transfusion reactions) Type III: Immune complex-mediated (e.g., serum sickness) Type IV: Cell-mediated (e.g., contact dermatitis)
Characteristics of each type in terms of mechanisms/targets/response time.

Transplantation

Allogeneic: most common type, the recipient's immune system is primed by the first encounter with donor antigen, and results in rejection when encountering the antigen again (second-set reaction).
Hyperacute rejection: rapid rejection due to pre-existing antibodies (e.g., ABO mismatch).
Acute rejection: T cell response rejection occurs within weeks due to antibodies and immune cells recognizing the graft cells as non-self.
Chronic rejection: occurs gradually over years, characterized by a loss of organ function.

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Description

Test your knowledge on various aspects of immunology, focusing on Type IV hypersensitivity and autoimmunity. This quiz covers the roles of Th1 CD4 cells, the Mantoux test, and the involvement of specific neurotransmitters. Additionally, explore the character of drugs inducing hypersensitivity reactions and the implications for cancer immunotherapy.