Disease of immunity Flashcards
Regarding HIV, which of the following statements is correct?
A There is an increase in delayed type hypersensitivity
B Can mount a normal antibody response to a new antigen
C Results in a polyclonal hypergammaglobulinaemia
D The decrease in CD8+ T cells is greater than the decrease in CD4+ T cells
C
Explanation
HIV results in a greater loss of CD4+ cells. There is an inversion of the CD4+:CD8+ ratio. HIV causes immunocompromise and the body has a decreased antibody response (inability to mount de novo antibody response to new antigens) with a decreased delayed type hypersensitivity. There is also decreased chemotactic and phagocytic response. Polyclonal B-cell activation leads to hypergammaglobuliaemia and circulating immune complexes.
Which of the following is NOT an AIDS defining infection?
A Coccidioidomycosis
B Disseminated salmonella infections
C Epstein–Barr virus (EBV)
D Toxoplasmosis
C
Explanation
AIDS defining infections include:
Protozoal and helminthic - pneumocytosis, toxoplasmosis, cryptosporidiosis.
note: pneumocytosis was original considered a protozoal infection. It is now however being considered to be a fungal infection
Fungal - candida, cryptococcus, disseminated histoplasmosis, coccidioidomycosis.
Bacterial - mycobacterium, disseminated salmonella infections.
Viral - cytomegalovirus (CMV), herpes simplex virus (HSV), varicella zoster virus (VZV).
AIDS defining neoplasms include :Kaposi sarcoma, beta cell non-Hodgkin lymphoma, primary lymphoma of the brain and invasive cancer of the uterine cervix
Note: I have added a reference from Wikipedia better defining what an AIDS defining illness is:
AIDS-defining clinical conditions (a.k.a. AIDS-defining illnesses or AIDS-defining diseases) is the list of diseases published by the centers for disease control and prevention (CDC) that are associated with AIDS, and used worldwide as a guideline for AIDS diagnosis. CDC exclusively uses the term AIDS-defining clinical conditions
According to the CDC definition, a patient has AIDS if they are infected with HIV and have either:
a CD4+ T-cell count below 200 cells/µL
a CD4+ T-cell percentage of total lymphocytes of less than 15%
or one of the defining illnesses.
A patient presenting one of the above conditions but with laboratory evidence against HIV infection is not normally considered to have AIDS
Which of the following is not a common AIDS defining opportunistic infection?
A Mycoplasma pneumonia
B Atypical mycobacteria
C Cytomegalovirus (CMV)
D Herpes Symplex Virus (HSV)
A
Explanation
Common AIDS defining opportunistic infection are
- Protozoal and helminthic infections: cryptosporidiosis and toxoplasmosis.
- Fungal infections: pneumocytosis, candidiasis and cryptococcosis.
- Bacterial infections: mycobacterium and salmonella.
- Viral infections: cytomegalovirus (CMV), herpes simplex virus (HSV).
Which of the following statements is correct in relation to hyperacute graft rejection?
A Spares vascular endothelium
B Is cell mediated
C Occurs in 1-4 days
D Decreases with cross matching
D
Explanation
Hyperacute graft reaction occurs within minutes to hours. The reaction is decreased with cross matching, however even with HLA class I and II matching, which will improve survival, immunosuppressive therapy is still required - except in identical twins. The reaction is Ag and Ab mediated and these are deposited as complexes in the vessel wall. The rejection occurs too early for the immunosuppressive drugs to be effective.
Hyperacute transplant rejection is due to which of the following mechanisms?
A Fibroblasts
B Fibrosis
C Immunoglobulin deposition
D Vasculitis
C
Explanation
Hyperacute Rejection. This form of rejection occurs within minutes or hours after transplantation. A hyperacutely rejecting kidney rapidly becomes cyanotic, mottled, and flaccid, and may excrete a mere few drops of bloody urine. Immunoglobulin-Antibody (HSRII) and complement are deposited in the vessel wall, causing endothelial injury and fibrin-platelet thrombi. Neutrophils rapidly accumulate within arterioles, glomeruli, and peritubular capillaries. As these changes become diffuse and intense, the glomeruli undergo thrombotic occlusion of the capillaries, and fibrinoid necrosis occurs in arterial walls. The kidney cortex then undergoes outright necrosis (infarction), and such nonfunctioning kidneys have to be removed.
Acute Rejection. This may occur within days of transplantation in the untreated patient or may appear suddenly months to years later, after immunosuppression has been ceased. In any one patient, cellular (HSR IV) or humoral immune mechanisms may predominate. Humoral rejection is associated with vasculitis, whereas cellular rejection is marked by an interstitial mononuclear cell infiltrate.
Regarding the rhesus blood group system which of the following statements is correct?
A Transfusion reactions will not occur if Rh negative people are given antigen
B 50% of caucasians are Rh Positive
C Rh negative refers to blood product being both D and E antigen negative
D There are very few spontaneous agglutinins within this system
D
Explanation
Rh refers to the D antigen, thus RH negative means D negative. However, at the basic level, Rh does refer to C, D and E antigens. Therefore Rh negative means C, D, E negative.
In contrast to the AB0 system, spontaneous agglutinins never occur in the Rh-system. 85% of Caucasians are Rh positive. The first transfusion of Rh+ blood will create anti D titres. The next transfusion, even years later, can cause a transfusion reaction
In relation to IgM, which of the following statements is correct?
A It is the largest antibody and the first to develop in the foetus
B It is antiviral
C It is a dimer structure
D It comprises 40% of normal circulating antibodies
A
Explanation
IgM is a pentamer or a hexamer. IgM levels comprise 120mg/dl circulating antibodies, IgG 1000mg/dl and IgA 200mg/dl. Its primary function is to activate complement.
75% of all circulating Ig is IgG, produced by plasma cells.
With regard to T lymphocytes, which of the following statements is correct?
A T cells contribute 40-50% of lymphocytes in the blood
B Differentiate into antibody producing plasma cells
C The T cell receptor complex contains CD3 complex proteins
D Are the basis for type 2 hypersensitivity reactions
C
Explanation
T lymphocytes develop from precursors in the thymus. Mature T cells are found in the blood, where they constitute 60-70% of blood lymphocytes. The T cell receptor (TCR) plus the CD3 molecular complex (proteins) form the TCR complex through which the T cell recognises the antigen. T cells express this TCR complex in all T Cells (and they are identical). The poteins are involved in the transduction of signals into the T cell after the TCR has bound to the antigen. T cells are the basis for Type IV delayed hypersensitivity. B cells differentiate into antibody producing plasma cells and are activated in the presence of soluble antigens
In transplant rejection, which of the following options is correct in relation to the hyperacute reaction?
A Due to a vasculitis
B Controlled by immunosuppressive drugs
C Cell mediated
D Prevented largely by cross-matching blood
D
Explanation
Hyperacute graft reaction occurs within minutes to hours. The reaction is decreased with cross matching but even with HLA class I and II matching, which will improve survival, you still need immunosuppressive therapy- except in identical twins. The reaction is Ag and Ab mediated and are deposited as complexes in the vessel wall. The rejection occurs too early for the immunosuppressive drugs to be effective.
All the following are type 1 hypersensitivity primary mast cell mediators, except?
A Eosinophil chemotactic factor (ECF)
B Platelet activating factor (PAF)
C Histamine
D Heparin
B
Explanation
Platelet activating factor is a secondary mediator. Other examples of secondary mediators include prostaglandin D2, leukotrienes, cytokines (NF, IL 1, 3, 4, 5,6). Other primary mediators include enzymes such as tryptase, chymase and acid hydrolase, eosinophil chemotactic factor, neutrophil chemotactic factor and adenosine.
Which of the following statements is true in relation to type 2 hypersensitivity?
A Includes serum sickness as an example
B Explains many transfusion reactions
C Involves cell mediated immune responses
D Involves IgE on mast cells
B
IgE on mast cells is type I.
Serum sickness is type III.
Cell mediated immune response is type IV.
A man with blood type B marries a woman with blood type AB. Which of the following opitons is correct?
A none of the above
B They cannot have a child with type A blood
C They cannot have a child with type O blood
D They cannot have a child with type AB blood
C
Explanation
The man could be heterozygous (one B allele and one O allele), or homozygous (two B alleles). The woman must be heterozygous (one A allele and one B allele). The following are the possible genotypes of their child: AB, AO, BO, BB. The potential phenotypes are type AB, type A or type B. They cannot produce a child with type O blood.
Passive immunity is achieved by administering which of the following?
A Activated T cells
B Adsorbed toxin
C Live virus
D Attenuated virus
A
Explanation
The one exception to passive-humoral immunity is the passive transfer of cell mediated immunity, also called adoptive immunisation, which involves the transfer of mature circulating lymphocytes. It is rarely used in humans and requires histocompatible (matched) donors, which are often difficult to find, and carries severe risks of graft versus host disease. This technique has been used in humans to treat certain diseases including some types of cancer and immunodeficiency. However, this specialised form of passive immunity is most often used in a laboratory setting
The majority of AIDS cases occur in which of the following groups in the USA?
A Blood product recipients
B Heterosexual adults
C Homosexual males
D IV drug abusers
C
Explanation
- Homosexual males 50%,
- Heterosexual contacts 33%
- IV drug users 25%,
- Recipients of blood transfusions 1%
- Haemophilliacs 0.5%
In the prescribed text: these figures reflect the trend in the USA. Note however that in Africa-especially sub-Saharan, the heterosexual group- is the most rapidly growing group, particulalry women, where the infection rate is estimated to be about 10000 cases every day
Which of the following reactions is cell mediated?
A Goodpastures syndrome
B Rheumatic fever
C Multiple sclerosis
D Arthus reaction
C
Explanation
Type I- (Immediate hypersensitivity)= anaphylaxis, allergies, bronchial asthma (atopic forms)
Type II (cytotoxic) - autoimmune haemolytic anaemia, erythroblastosis foetalis, rheumatic fever, goodpastures, grave’s disease
Type III (immune-complex) - SLE, certain forms of glomerulonephritis, Arthus reaction, serum sickness
Type IV- hypersensitivity reaction (Cell mediated hypersensitivity)= multiple sclerosis, TB, contact dermatitis, type I DM, RA, IBD, graft vs host disease
All of the following are opportunistic AIDS infections, except?
A Mycoplasma pneumonia
B Cytomegalovirus (CMV)
C Pneumocystis jirovecii
D Atypical mycobacterium
A
Explanation
AIDS defining illnesses include infections and neoplasms.
AIDS defining infections include:
Protozoal and helmintic- pneumocytosis, toxoplasmosis, cryptosporidosis.
Fungal-candida, cryptococcus, disseminated histoplasmosis, coccidiodomycosis.
Bacterial- mycobacterium, disseminated salmonella infections.
Viral- cytomegalovirus (CMV), herpes simplex virus (HSV), Varicella zoster virus (VZV).AIDS defining neoplasms include: Kaposi sarcoma, beta cell non-Hodgkin lymphoma, primary lymphoma of the brain and invasive cancer of the uterine cervix
Note: Pneumocystis carinii pneumonia is now known as Pneumocystis jirovecii
Which hypersensitivity reaction is poststreptococcal glomerulonephritis?
A Type IV HSR
B Type III HSR
C Type I hypersensitivity reaction (HSR)
D Type II HSR
B
Explanation
Acute rheumatic fever is a type II HSR: streptococcal cell wall antigen; antibody cross reacts with myocardial antigen.
Poststreptococcal glomerulonephritis is a type III HSR: streptococcal cell wall antigen(s); may be planted in glomerular basement membrane
Mnemonic to remember hypersensitivity reactions: “ACID”
Anaphylactic type: type I
Cytotoxic type: type II
Immune complex disease: type III
Delayed hypersensitivity (cell mediated): type IV
Eg:
Type I- (Immediate hypersensitivity)= anaphylaxis, allergies, bronchial asthma (atopic forms)
Type II (cytotoxic hypersensitivity) - autoimmune haemolytic anaemia, erythroblastosis foetalis, rheumatic fever, goodpastures, grave’s disease
Type III (immune complex) - SLE, certain forms of glomerulonephritis, Arthus reaction, serum sickness
Type IV- hypersensitivity reaction (Cell mediated hypersensitivity)= multiple sclerosis, TB, contact dermatitis, type I DM, RA, IBD, graft vs host disease
If both parents have blood group B. What type of blood group cannot appear in their children?
A AB
B O
C B
D OB
A
Explanation
The man could be heterozygous (one B allele and one O allele), or homozygous (two B alleles). The woman could be heterozygous (one B allele and one O allele), or homozygous (two B alleles). The following are the possible genotypes of their child: B, OB, O. They cannot produce a child with type AB blood.
Note: similar to another blood group MCQ- but it is good to practice
Which of the following is true regarding Agammaglobulinemia
A Recurrent respiratory tract infections are the most common presentations
B It becomes apparent in the first month of age
C It is a deficiency of cell mediated immunity
D It is a autosomal dominant inherited disease
A
Explanation
X-linked agammaglobulinemia is one of the more common forms of primary immunodeficiency. It is characterised by the failure of B cell precursors to develop into mature B cells. It is a disease of the humoral arm of adaptive immunity. Because it is X linked, it appears almost entirely in males but sporadic cases have occurred in females due to mutations in some other gene that functions in the same pathway. The disease seems to appear only after 6 months of age, as maternal immunoglobulins are depleted. Recurrent bacterial infections of the respiratory tract are the most common and allude to the underlying immune deficiency. Most often the causative organism is H influenza, Sterp pneumoniae and staf aureus. Viral infections also occur because antiboides are important for neutralisin viral infections. Common viral infections include polio, enterovirus, echovirus and coxsackievirus. Treatment involves prophylactic intravenous Ig therapy.
A 5yr old girl presents to the emergency department with malaise, fever, nausea, oliguria and haematuria. You identify red cell casts in her urine. What is the most likely diagnosis?
A Membranous glomerulopathy
B Minimal change disease
C Post streptococcal glomerulonephritis
D Focal, segmental glomerulonephritis
C
Explanation
Poststerptococcal glomerulonephritis usually appears 1-4 weeks after a streptococcal throat or skin infection. It occurs most frequently in ages 6-10yrs, but adults of any age can be affected. The A beta haemolytic streptococci are the causative agents, but only certain strains are nephrogenic. More than 90% of cases being traced to types 12, 4 and 1.
It is an immune mediated disease-type III hypersensitivity reaction.
Clinical picture: abrupt malaise, fever, nausea, oliguria and haematuria 1-2 weeks after recovery form a sore throat. The patients have red cell casts in the urine, mild proteinuria (<1gm/day), periorbital oedema and mild to moderate hypertension. More than 95% of cases eventually recover with only conservative therapy of maintaining a salt and water balance. Few progress to a chronic glomerulonephritis with or without recurrence of an active nephritic picture. Adults present more atypically with the sudden appearance of hypertension., oedema with the elevation of the renal urea and creatinine.
Minimal change disease is associated with children, but it typically does NOT present with haematuria.
Type I Diabetes is which if the following hypersensitivity reactions?
A Hypersensitivity reaction 1
B Hypersensitivity reaction 2
C Hypersensitivity reaction 4
D Hypersensitivity reaction 3
C
Explanation
IDDM is a type IV hypersensitivity reaction
It is thought that during early life, damage to islet cells leads to exposure of islet cell antigens to CD4+ Th1 cells in peri pancreatic lymph. Activated T cells are then trafficked to the pancreas and cause B cell injury. There is thus a failure of self-tolerance in T cells which may be due to defective clonal deletion or regulatory processes. A role for antibodies has been suspected as most patients have autoantibodies against islet antigens, however it is unclear if the antibodies are involved in causing injury or are produced as a consequence of islet cell damage. Therefore, it is classed as a Type IV hypersensitivity reaction
A 6yers old female presents to the ED with lethargy, polydipsia, polyuria. Blood sugar reads>20mmol/l. The mechanism of disease is the following?
A Type IV HSR
B Type III HSR
C Type I HSR
D Type II HSR
A
Explanation
Hypersensitivity reactions
Type IV= type I diabetes mellitus
Antigens of pancreatic islet B cells (insulin, glutamic acid decarboxylase, others)
Mechanism of disease insulitis (chronic inflammation in islets), destruction of B cells
Causes IDDM-type 1 DM
A 7-year-old who develops shortness of breath and wheeze in response to pollen exposure is suffering a hypersensitivity reaction, type:
A IV
B III
C I
D II
C
Explanation
Atopic asthma is a type I hypersensitivity reaction whereby allergen exposure causes bronchostriction and an inflammatory response of airways.
Anti-D is sometimes given in pregnancy to prevent which type of hypersensitivity reaction?
A IV
B III
C I
D II
D
Explanation
Type II hypersensitivity reactions are antibody-mediated. Transfusion reactions occur due to antigen re-exposure causing opsonization and phagocytosis by pre-formed antibodies (antibody-dependent cell-mediated cytotoxicity)
Which of the following is a live vaccine?
A Hepatitis B
B Rabies
C Hepatitis A
D Varicella
D
Explanation
The varicella vaccine is a live vaccine with an attenuated portion of virus with reduced virulence.
Mantoux skin testing demonstrates what sort of hypersensitivity reaction?
A Type IV cell-mediated hypersensitivity
B Type IV antibody-antigen mediated hypersensitivity
C Type III antibody-antigen mediated hypersensitivity
D Type III cell-mediated hypersensitivity
A
Explanation
A positive tuberculin test signifies T-cell–mediated immunity to mycobacterial antigens but does not differentiate between infection and active disease.
