Ultimate USMLE Step 1 Exam Prep:
Comprehensive Questions, Detailed
Answers, and Thorough Rationales for
Guaranteed Success 2024
Comprehensive USMLE Step 1 Exam
Bank: 101+ High-Yield Questions,
Detailed Answers, and Rationales for
Guaranteed Success
When Stem cells start to rearrange gene segments to become B cells what happens first.
A. D gene rearranges with a V gene.
B. V gene rearranges with the C Gene
C. D gene rearranges with a J gene
D. V gene rearranges with a J gene
E. D gene rearranges with the C gene.
Answer C: The first rearrangement in immunoglobulin genetics is the D and J rearrangement in
the early pro-B cell.
,Isotype switching during B Cell ontongeny dedicates mature B cells to production of single,
heavy chain isotope, except in the case of IgM and IgD, which can be expressed concomitantly.
This expression of both iostypes simultaneously is possible due to?
A. Allelic exclusion
B. Allelic codominance
C. Affinity maturation
D. Alternative RNA splicing
E. Somatic hyper mutation
Answer D. Alternative RNA splicing allows a mature B cell to attach either delta or mu chains on
a single idiotype that has been gernated by germ-line DNA rearrangments. Allelic exclusion
refers to the expresion of either parental chromosome type but not both, and codominance does
not occur in the alleles for Ig synthesis. Affinity maturation refers to the increase of affinity of a
population of antibodies over time of immunization, and somatic hypermutation is the
phenomenon that allows affinity maturation to occur.
The genetic diversity of T-cell antigen receptors is very similar to that of the B - Cell antigen
receptor. Which of the following does not contribute to the development of antigenic repertoire in
T cells?
A. 50-100 choices of varaible alpha and beta genes.
B. Multiple J gene segment codons.
C. Junctional variability in alpha and beta molecules
D. Somatic Hyper mutation
E. Random combination of alpha and beta chains.
Answer: D, Somatic hyper mutation, which is important in the development of affinity maturation
in B-cell populations , is not present in T cells undergoing selection of their antigenic repertoire.
This is very critical for the immune response because T cells are subjected to rigorous positive
and negative selection in the thymus for the ability to correctly recognize self and non-self, and
hyper mutation after encountering antigen (such as occurs in B cells) would be a potential
mechanism for the development of auto reactivity. All of the other mechanisms to increase
antigen-recognizing diversity are used by both T and B cells.
,Which one of the following is one of the major interleukins produced by CD4+ T helper
A. IL-1
B. IL-2
C. IL-4
D. IL-8
E. IL-6
Answer B: This IL-2 stimulates NK cells, and Cd8+ T cytotoxic lymphocytes. It also combines
with its own IL-2 receptors and stimulates itself. It is involved in down ergulating Cd4+ T helper
2 lymphocytes
Which one of the following best describes a superantigen?
A. Bacterial product that binds to beta chain of TCR and MHC class II molecules of APC
stimulating T cell activation.
B. Bacterial product that binds to CD4+ molecule causing T-cell activation.
C. Bacterial product that binds to B7 and Cd28 costimulatory molecules
D. Bacterial product that stimulates massive amounts of IgG antibody due to its large size.
E. Bacterial product that is presented by macrophages to larger than normal number of T helper
Cd4+ lymphocytes.
Answer: A. The superantigen such as TSST-1 or staphylococcal enterotoxin crosslinks the
variable domain of the TCR beta chain to the MHC class II molecule and specifically induces
massive T cell activation
When a Th 0 (T Helper 0) cell matures in the presence of IL-4 and IL-5 they become?
A.Cytoxic T cell
B. Supressor T cell.
C. T-helper 1 cell
D. T helper 2 cell
E. Thymic T Cell.
Answer D. The Il-4 and IL-5 interleukins stimulate the T cells that are moer involved in
stimulating future antibody production. These T cells that are involved in stimulating antibody
production are T helper 2 cells.
, Which of the following cytokines are associated with the development of cell mediated
immunity?
A. Il-4
B. IL-5 and IL-10
C. Gamma interferon and IL-12
D. IL-4 and IL-3
E. IL-10 and IL-3
Answer C: Gamma interferon from T-helper 1 Cd4+ lymphocytes and Il-12 from macrophages
are major stimulators of the development of a cell mediated immune response to intracellular
organisms such as tuberculosis, leishmaniasis, histoplasmoisis and many other organisms.
Produced by a variety of cells; main function is to inhibit viral replication.
A. Interferon gamma
B. Interleukin 2
C. Interleukin 1
D. Interferon Beta
E. Interleukin 5
F. Interleukin 8
D - interferon - Beta is produced by a wide variety of cell types (i.e fibroblasts) and is a potent
inhibitor of viral replication
Produced by helper T cells; main role is in antibody class switching and B cell differentiation.
A. Interferon gamma
B. Interleukin 2
C. Interleukin 1
D. Interferon Beta
E. Interleukin 5
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