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USMLE Step 1 Immunology

Subjects : health-sciences, usmle-step-1

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Answer 50 questions in 15 minutes.
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1. What are complements in the complement system? What activates them? there seems to be different ones - What are these pathways called?
Axillary
Barrel hoop basement membrane fenestrations
HBV - HBC - Kaposis - leukemias - malignant melanoma - hairy cell leukemia and condyluma accuminata
Proteins; IgG - IgM - endotoxin (microbial surfaces in general - nonspecific ones also) - mannose binding Lectin; classic - alternative - MB pathway (resp)

2. Describe the interstitial tissue of a spleen including the sinuses. What type of cells are found in the four structures (cortex - paracortex - medulla and sinuses)?
The interstitial tissue of a lymph node is structured into the cortex on the outside Which is densely cellular which transitions into the paracortex Which is less dense and then the medulla Which is least dense. The cells that inhabit these tissues a
2 heavy chains and two light chains
CD21 on B cells (although there is T cell lymphocytosis in EBV)
RNA segment reassortment

3. What are the three types of lymphocytes?
B - T - and NK cells
Interferon gamma and IL 2
not Ab mediated
Induces fever - chemokine secretion to recruit - activates adhesion molecules; macrophages

4. are Th cells involved in trapping of antigens of endotoxin/LPS?
Pernicious Anemia and Hashimotos
No because no peptide fragment!
C5a
Give a vaccine with a peptide comp from it that the cell mediated immunity otherwise cant get to! like h.influenzae vaccine. then class switching and memory response can occur

5. Which disease is associated withB B27?
Antimicrobial also secreted by CD8 and NK cells that induces apoptsosis
Psoriasis - Ankylosis Spondylitis - IBD - Reiters; all seronegative spondylopathies
N. meningitidis - H. influenzae - S. pneumonia - Salmonella d/t lack of C3b opsonization for MAC d/t lack of complement activation d/t lack of IgM; MAC is needed by encapsulated avoid by humoral and cell mediated through their capsule
Influenza; antigenic shift; antigenic drift

6. What are the autoantibodies for wegeners granulomatosis?
Scratch test - histamine mediated wheal; radioimmunosorbent assay (detects specific IgEs in serum)
An alpha and beta chain; only on APCs; TCR and CD4; extracellular (phagocytosed by APCs)
T cell dysfunction
C - ANCA (antiproteinase); in neutrophil; c= cytoplasmic

7. Which is the main antibody in the delayed or secondary response to an antigen?
DM type I
T cell dysfunction
Can be acquired in 20s -30s; increased risk of autoimmune disease - lymphoma - Sp infections; normal number of B cells and no plasma cells and immunoglobulin
IgG

8. What lymph node drains the breast?
Axillary
In the germinal center of secondary follicles (In the paler center)
From self; from identical twin or clone; from nonidentical individual of same species; from different species; fetus; pig valve
Anticentromere; anti Scl -70 (anti DNA topoisomerase I)

9. Describe the capsular structure of a lymph node; What are the functions of the LN?
Recom IL 11; thrombocytopenia
IgM and IgG
Capsule of lymph node is made up of type III collagen (made by reticulin fibers!) - extension of this collagen extends into the splenic tissue as trabeculae; nonspecific filtration of lymph by Macrophages - Antibody production (via activation) - stor
Antimicrosomal and antithyroglobulin

10. which cytokine inhibits TH2 cells? secreted by who?
Interferon gamma; Th1
Activate B cells - activate Macrophages - kill viruses directly - delayed cell mediated hypersensitivity - acute and chronic rejection
Basophils! THey want IG E class switch!
cannot cross placenta

11. What is the pathogenesis of a candida skin test?
Delayed type hypersensitivity
N. meningitidis - H. influenzae - S. pneumonia - Salmonella d/t lack of C3b opsonization for MAC d/t lack of complement activation d/t lack of IgM; MAC is needed by encapsulated avoid by humoral and cell mediated through their capsule
The antibodies (igM or IgG) either neutralize the target directly (cytoxic!) or recruit leukocytes (Neutrophils and Macrophages!) to incite tissue damage
secondary

12. What bugs can actually infect the lymph node itself?
Cell mediated due to T cell cytotoxicity reacting to foreign MHCs; few weeks after
Viral neutralization of igM and IgG!
Mycobacterium Tuberculosis - Mycobacterium Avium Intracellulare; Toxoplasmosis Gondii
Histamine; post capillary venules - vasodilation

13. Describe complement dependent Type II hypersensitivity. Give an example.
IgE
Proteins; IgG - IgM - endotoxin (microbial surfaces in general - nonspecific ones also) - mannose binding Lectin; classic - alternative - MB pathway (resp)
1) susceptibility to encapsulated organisms 2) Howell Jolly Bodies 3) Target cells 4) Thrombocytosis
IgM or IgG antibodies coat the antigen and result in activation of MAC complex via the classical pathway OR fixed macrophages in the spleen phagoctyose the opsonized (C3b or igG) antigens - ex penicillin reaction; IgM AIHA - anti B IgMs in a group A

14. Which TCR MHC system is important for viral immunity? neoplastic? donor graft cells?
Anti nuclear Antibodies (ANA); Anti dsDNA - anti Smith
Influenza; antigenic shift; antigenic drift
Severe recurrent pyogenic sinus and resp tract And increased susceptibility to type III hypersensitivity like SLE
All MHC 1/CD8

15. IgG...
Can be acquired in 20s -30s; increased risk of autoimmune disease - lymphoma - Sp infections; normal number of B cells and no plasma cells and immunoglobulin
The interstitial tissue of a lymph node is structured into the cortex on the outside Which is densely cellular which transitions into the paracortex Which is less dense and then the medulla Which is least dense. The cells that inhabit these tissues a
opsonizes
Not thymus - BM

16. What are the autoantibodies for hashimotos?
Antimicrosomal and antithyroglobulin
Th1; interferon gamma; IL 2 for cytotoxic T cell activation
Influenza; antigenic shift; antigenic drift
IL 5

17. what will NK cells do to cells covered in IgG Ab? why?
Kill them because they have CD16 on them that recognize the FcG portion
IgM or IgG antibodies coat the antigen and result in activation of MAC complex via the classical pathway OR fixed macrophages in the spleen phagoctyose the opsonized (C3b or igG) antigens - ex penicillin reaction; IgM AIHA - anti B IgMs in a group A
Cross link
Trypanosomes with programmed rearrangement (results in recurring fever -- sleeping sickness!)

18. What does granzyme do? who secretes it?
Decreased Th1 response; disseminated mycobacterial infections; decreased interferon gamma
Its a serine protease that activates apoptosis; NK and CD8
Anti mitochondrial
Graves

19. What is thrombopoietin used for?
Maculopapular rash (palm - soles - back - neck) - jaundice with bile duct necrosis - hepatosplenomegaly - diarrhea; bone marrow and liver transplants (rich with lymphocytes); SCID patient receiving whole blood transfusion
Macrophages - Dendritic cells - B cells
Inferior mesenteric
Thrombocytopenia

20. What amine is the main chemical mediator released by mast cells? Where does it act What does it result in?
Axillary
Inferior mesenteric
Interferon gamma; Th1
Histamine; post capillary venules - vasodilation

21. What is an example of a parasite showing antigenic variation?
Trypanosomes with programmed rearrangement (results in recurring fever -- sleeping sickness!)
TNF alpha and IL1
secondary
SP infections

22. How do endotoxin/LPS of gram negative bacteria stimulate the immune system if they do not have a peptide fragment?
Recomb cytokine of GCSF (granulocyte macrophage colony stimulating factor; for recovery of bone marrow
They directly stimulate Macrophages by binding CD14; also the alternative complement pathway binds to these host surfaces and induces MAC complex; also TLRs exist for endotoxins; also IgM though not an opsonin can act as a pentamer and trap the antig
MHC I; from RER with help of the B2 microglobulin
cannot cross placenta

23. What do mature naive B lymphocytes express?
Tumor cells and virally infected cells; perforin pore to secrete granzymes through it; apoptosis
Influenza; antigenic shift; antigenic drift
IgM and IgG
IgM and IgD

24. Often bacteria are associated with being killed by humoral immunity. Name some bugs that require cell mediated immunity because they evade humoral response
Since cant cross placenta most likely means that child was forced early to produce due to an infection (most likely CMV)
Legionella - N. gonorrhea - L. monocytogenes - viruses - protozoa (leismaniasis)
Make antibody - allergy type 1 (igE) - Cytotoxic and immunecomplex hypersensitivity type II and III (igG); hyperacute organ rejection is Ab mediated
IgE; by activating eosinophils

25. Which Thelper cell activated Macrophages? by secreting what? what else does Th1 secrete? For what?
Immune complex - Arthus reaction and Serum sickness; they are all a result of antibody- antigen complex deposition resulting in complement activation
Th1; interferon gamma; IL 2 for cytotoxic T cell activation
except hyperacute
The patient could become cyanotic in the OR!

26. How is i Th1 helper cell inhibited?
Cytokine IL 10 secreted by Th2
Monoclonal Ab to CD3- blocks cellular transduction and signaling of T cells
CGD; Jobs syndrome (defect in Neutrophil chemotactic response)
pentamer

27. What is the main function of IL 12? other than macrophages who else can release IL 12?
mesenchymal
Induce differentiation of T cells into Th1 helper cells and activates NK cells also; B cells
acute phase reactants
Complement activation (active in both)

28. What happens in a deficiency of C3?
Interferon gamma; Th1
Severe recurrent pyogenic sinus and resp tract And increased susceptibility to type III hypersensitivity like SLE
Tetanus - Botulinum - HBV - Rabies
Anti viral and anti tumor

29. what prevents NK cells from killing normal cells if their default is to kill?
MHC class molecules bind to KIRS or CD94 to prevent killing
Liver! (they are proteins circulating in the blood)
Acts as second signal on B cells to induce class switching to IgE and IgG
Para aortic

30. How is the thymus organized? what happens in each section?
When you select for which MHC it will have; take out the lymphs that self react
Into cortex and medulla; cortex is where immature T lymphocytes enter - at the corticomedullar junction is where positive and negative selection occur; and at the medulla is where the mature T lymphs - reticulin cells and hassalls corpuscles are (dea
Anticentromere; anti Scl -70 (anti DNA topoisomerase I)
The igA found in breast milk

31. What is passive immunity?
Axillary
Receiving preformed Antibodies
TGF beta and IL 10
Lack of response from lymphocytes when activated; because they are self reactive - this is a form of tolerance

32. What are the PALS?
Periarteriolar lymphatic sheath in the white pulp that surround that dead end of the capillaries in the red pulp - contain T cells
Chronic granulomatous disease
Can be acquired in 20s -30s; increased risk of autoimmune disease - lymphoma - Sp infections; normal number of B cells and no plasma cells and immunoglobulin
Carbohydrate

33. How does the alternative pathway lead to MAC activation?
Soluble C3 spontaneously hydrolyzes spontaneously to C3b and opsonizes microbial and host cell surfaces and accumulates on surfaces; C3b activates C5 convertase which leads to MAC activation
Binds to Mtor which (like tacrolimus and cyclosporine just in a different pathway) inhibits IL 2 production and thus t cell proliferation in response to IL 2 producton
MHC II - B7 - CD40 and CD14; CD40 and D14 for FcG and C3b resp
An alpha chain and a B2 microglobulin; on all nucleated cells; TCR and CD8; intracellular antigens

34. What is the defect in hyper IgM syndrome? What are the lab results?
Superior mesenteric
Patient has had previous exposure to blood products which result in presence of preformed anti HLA cytotoxic Abs
Defect in CD40L results in inability to class switch; a lot of IgM and no IgG - A - E
Some microbial surfaces (only) have mannan binding lectin which activates a protease that cleaves C2 and C4 which combine to make C3. the rest follows the alternative pathway

35. What are the autoantibodies for drug induced lupus?
Antihistone
Bind FcG for antibody dependent cellular cytotoxicity
Hereditary angioedema; PNH
MAC (membrane attack complex) Which is activated by C5b - C9 and results in lysis and cytoxicity by creating pores in the target membrane; encapsulated organisms (S. pnuemonia - H.influenzae - B perfussis for example) and other organisms with non pep

36. What cytokines to Th2 secrete?
IL 4 - 5 - 10 - 6
cannot cross placenta
Superficial inguinal
Brain - eyes - placenta/fetus - testicles; because they can have an antigen in there and not get attacked by immune system because dont have contact with immune system via blood and lymph; if an infection occurs such that trauma results in exposure t

37. What is a type I hypersensitivity reaction? What is atopic?
except hyperacute
MHC II - B7
An anaphylactic immediate reaction; atopy refers to the inherited propensity to develop asthmatic or allergic reactions
Antibody mediated cytotoxicity; either complement dependent or complement independent

38. What are the autoantibodies for Mixed connective tissue disease?
Stimulate the liver to release acute phase reactants
Anti U1 RNP (ribonucleoprotein)
Antidote for digoxin intoxication
Isotype switching (activated by Th2 cell signals and cytokines) - somatic hypermutation

39. What is the main cytokine that activates eosinophils?
IL 5
HBV - HBC - Kaposis - leukemias - malignant melanoma - hairy cell leukemia and condyluma accuminata
It is a localized type III hypersensitivity reaction to an external antigen; localized instead of systemic; ?; intradermal injection of the antigen results in antibody production and antigen antibody complexes deposit in the skin
Rheumatic arthritis

40. What lymph node drains the stomach?
Secretory component
Decreased Th1 response; disseminated mycobacterial infections; decreased interferon gamma
Celiac
In IgE AIHA- it results in MAC attack (remember IgE is not an opsonin!) - in IgG AIHA C3b (and IgG) opsonization results in phagocytosis by fixed macrophages in the spleen

41. What are the mediators that mast cells release?
Histamine (causes vasodilation) - leukotrienes (causes bronchoconstriction) - chemotaxins for eos - and heparin (increased blood flow needs to be anticoagulated!)
Opsonize bacteria (for enhanced phagocytosis) - neutralize viruses (igG) - activate complement (igM and igG) - sensitize mast cells (igE)
Anti glutamate carboxylase and anti insulin
Vasculitis of graft vessels with dense interstitial lymphocytic infiltrate; yes! with immunosuppressants

42. For which toxins are preformed antibodies (passive) given?
IL 4 - 5 - 10 - 6
Recomb cytokine of GCSF (granulocyte macrophage colony stimulating factor; for recovery of bone marrow
Tumor cells and virally infected cells; perforin pore to secrete granzymes through it; apoptosis
Tetanus - Botulinum - HBV - Rabies

43. What type of fenestrations are found in the red pulp of the spleen?
Th1; interferon gamma; IL 2 for cytotoxic T cell activation
Celiac
Barrel hoop basement membrane fenestrations
The red pulp of the spleen its where the vasculature channels go through and interact with the parenchyma of the spleen (has macrophages) which empty in the sinuses; they are both encapsulated (with trabeculae) secondary lymphoid organs that trap ant

44. How do you test for type III hypersensitivity?
Immunoflourescent staining of tissue biopsies
...
Intracellular pathogens (acute and chronic viruses and virally induced cancers)
MS - hay fever - SLE - goodpastures

45. Which HLA's are included in MHC I? MHC II?

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46. which of the hypersensitivity reactions is not Ab mediated?
Type IV
Aut. Dominant; C1 esterase inhibitor deficiency resulting in continued C1 which results in increased C2 and C4 cleavage products which have anaphyltoxic activity and result in swelling of face and oropharynx
TNF alpha and IL1
Anti topoisomerase

47. What are some sinopulmonary infections?
Sinusitis - otitis media - pneumonia
Wiskott Aldrich syndrome
Fc
MAC (membrane attack complex) Which is activated by C5b - C9 and results in lysis and cytoxicity by creating pores in the target membrane; encapsulated organisms (S. pnuemonia - H.influenzae - B perfussis for example) and other organisms with non pep

48. How do we use thymus dependent antigens to prevent infection from organisms that lack a peptide component?
Hours later (instead of minutes); instead of release of preformed mediators - mast cells synthesize PGs and LTs that mediate the late phase reaction (edema - inflammation - decreased airflow)
Give a vaccine with a peptide comp from it that the cell mediated immunity otherwise cant get to! like h.influenzae vaccine. then class switching and memory response can occur
DM type I and RA
Antibody mediated cytotoxicity; either complement dependent or complement independent

49. What is the pathogenesis of acute transplant rejection? When does it occur?
Cell mediated due to T cell cytotoxicity reacting to foreign MHCs; few weeks after
Glycoproteins; HLA
No because no peptide fragment!
Paracortex; viral infection

50. If an antigen lacks a peptide component How does the adaptive immunity attack it? What type of response is this called. give an example of bugs that do this. what implications does this have on splenectomy?
This means that MHC can not recognize it and thus will not be phagocytosed. The humoral response rescues - IgM is the primary response attack. Since there is no class switching (without MHC activation no CD40 L and interleukins to activate!) then the
An anaphylactic immediate reaction; atopy refers to the inherited propensity to develop asthmatic or allergic reactions
Decreased Th1 response; disseminated mycobacterial infections; decreased interferon gamma
Influenza; antigenic shift; antigenic drift

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USMLE Step 1 Immunology

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