USMLE STEP 1 IMMUNOLOGY FINAL EXAM 2025/2026
QUESTIONS WITH ANSWERS GRADED A+
✔✔Which immunoglobulin isotype prevents attachment of bacteria and viruses at
mucous membrane, does not fix complement, forms a dimer when secreted, is found in
tears, saliva, mucus and breast milk and picks up a secretory component from epithelial
cells before secretion? - ✔✔IgA
✔✔Which immunoglobulin isotype has an unclear function andis found on the surface of
many B cells and in the serum at low amounts? - ✔✔IgD
✔✔Which immunoglobulin isotype is produces in the immediate response to an antigen,
fixes complement, does not cross the placenta, is either a monomer or a pentamer and
therefore capable of binding up to 10 Ag? - ✔✔IgM
✔✔Which immunoglobulin isotype binds mast cells and basophils, cross-link when
exposed to an allergen, mediates type 1 hypersensitivity through release of histamine,
mediated immunity to worms by activating eiosinophils and has the lowest concentration
in the serum? - ✔✔IgE
✔✔What are thymus-independent antigens? - ✔✔Antigens lacking a peptide
component and thus cant be presented by MHC to T cells and allow for immunologic
memory (e.g. LPS of gram negative bacteria)
✔✔Myeloperoxidase deficiency results in chronic infectious of what type? - ✔✔Fungal
✔✔What are the 3 most common chemoattractants? - ✔✔IL-5, C5a, Leukotriene B4
✔✔What complement componenet is crucial for opsonization, binding bacteria? -
✔✔C3b
✔✔What 2 complement components are crucial for anaphylaxis? - ✔✔C3a, C5a
✔✔Deficiency in C1 esterase inhibitor leads to what disorder? - ✔✔Hereditory
Angioedema
✔✔Deiciency in what complement components leads to neisseria bactremia? - ✔✔C5-
C8
✔✔What two cytokines released from macrophages are endogenous pyogens? - ✔✔IL-
1, IL-6
✔✔What cytokine release from macrophages mediates sepsis? - ✔✔TNF-a
, ✔✔What cytokine supports the growth anf differentiation of bone marrow stem cells and
what cells secrete it? - ✔✔IL-3; T-cells
✔✔What cytokine induce the differentiation into TH2 cells and enhances class switching
to IgE and IgG? - ✔✔IL-4
✔✔What cytokine enhances class switching to IgA? - ✔✔IL-5
✔✔What proteins place uninfected cells in an antiviral state and induce the produciton
of a ribonuclease that inhibits viral protin synthesis by degrading viral mRNA? - ✔✔IFN
a, B, gamma
✔✔What is the Fc receptor for IgG found on NK cells, monocytes, macros and
nuetrophils? - ✔✔CD16
✔✔What sexually transmited virus req. Ab-mediated cell-mediated cytoxcitiy (ADCC)
due to its ability to down regulate the expression on MHCI cell surfaces? - ✔✔Herpes
✔✔What do we call a bacterial toxin that crosslinks the beta region of TCR and MHCII
on APC in the absence of a secific Ag and cause an uncontrollable release of
cytokines? - ✔✔SuperAntigen
✔✔What is the receptor for Ebstein-Barr on B-cells? - ✔✔CD21
✔✔What is anergy? - ✔✔lack of response or reactivity due to their being no
costimulatory signal
✔✔endotoxin/LPS binds directly to endotoxin receptor _____ on macrophages. -
✔✔CD14
✔✔Name the hypersensitivity type: IgE and mast cell/basophil mediated, rapid reaction
due to preformed antibodies bound to mast cells/basophils. - ✔✔Type 1
✔✔What type of hypersensistivity results in anaphylaxis? - ✔✔Type 1
✔✔What hypersentivity reaction type is not mediated by antibodies? - ✔✔Type 4
✔✔Name the hypersensitivity type: IgM and IgG binding to fixed antigen on enemy cell,
leading to lysis by complement of phagocytosis. - ✔✔Type 2
✔✔Name the hypersensitivity type: Ab-Ag complexes activate complenet and large
immune complex gets stuck in tissues - ✔✔Type 3
QUESTIONS WITH ANSWERS GRADED A+
✔✔Which immunoglobulin isotype prevents attachment of bacteria and viruses at
mucous membrane, does not fix complement, forms a dimer when secreted, is found in
tears, saliva, mucus and breast milk and picks up a secretory component from epithelial
cells before secretion? - ✔✔IgA
✔✔Which immunoglobulin isotype has an unclear function andis found on the surface of
many B cells and in the serum at low amounts? - ✔✔IgD
✔✔Which immunoglobulin isotype is produces in the immediate response to an antigen,
fixes complement, does not cross the placenta, is either a monomer or a pentamer and
therefore capable of binding up to 10 Ag? - ✔✔IgM
✔✔Which immunoglobulin isotype binds mast cells and basophils, cross-link when
exposed to an allergen, mediates type 1 hypersensitivity through release of histamine,
mediated immunity to worms by activating eiosinophils and has the lowest concentration
in the serum? - ✔✔IgE
✔✔What are thymus-independent antigens? - ✔✔Antigens lacking a peptide
component and thus cant be presented by MHC to T cells and allow for immunologic
memory (e.g. LPS of gram negative bacteria)
✔✔Myeloperoxidase deficiency results in chronic infectious of what type? - ✔✔Fungal
✔✔What are the 3 most common chemoattractants? - ✔✔IL-5, C5a, Leukotriene B4
✔✔What complement componenet is crucial for opsonization, binding bacteria? -
✔✔C3b
✔✔What 2 complement components are crucial for anaphylaxis? - ✔✔C3a, C5a
✔✔Deficiency in C1 esterase inhibitor leads to what disorder? - ✔✔Hereditory
Angioedema
✔✔Deiciency in what complement components leads to neisseria bactremia? - ✔✔C5-
C8
✔✔What two cytokines released from macrophages are endogenous pyogens? - ✔✔IL-
1, IL-6
✔✔What cytokine release from macrophages mediates sepsis? - ✔✔TNF-a
, ✔✔What cytokine supports the growth anf differentiation of bone marrow stem cells and
what cells secrete it? - ✔✔IL-3; T-cells
✔✔What cytokine induce the differentiation into TH2 cells and enhances class switching
to IgE and IgG? - ✔✔IL-4
✔✔What cytokine enhances class switching to IgA? - ✔✔IL-5
✔✔What proteins place uninfected cells in an antiviral state and induce the produciton
of a ribonuclease that inhibits viral protin synthesis by degrading viral mRNA? - ✔✔IFN
a, B, gamma
✔✔What is the Fc receptor for IgG found on NK cells, monocytes, macros and
nuetrophils? - ✔✔CD16
✔✔What sexually transmited virus req. Ab-mediated cell-mediated cytoxcitiy (ADCC)
due to its ability to down regulate the expression on MHCI cell surfaces? - ✔✔Herpes
✔✔What do we call a bacterial toxin that crosslinks the beta region of TCR and MHCII
on APC in the absence of a secific Ag and cause an uncontrollable release of
cytokines? - ✔✔SuperAntigen
✔✔What is the receptor for Ebstein-Barr on B-cells? - ✔✔CD21
✔✔What is anergy? - ✔✔lack of response or reactivity due to their being no
costimulatory signal
✔✔endotoxin/LPS binds directly to endotoxin receptor _____ on macrophages. -
✔✔CD14
✔✔Name the hypersensitivity type: IgE and mast cell/basophil mediated, rapid reaction
due to preformed antibodies bound to mast cells/basophils. - ✔✔Type 1
✔✔What type of hypersensistivity results in anaphylaxis? - ✔✔Type 1
✔✔What hypersentivity reaction type is not mediated by antibodies? - ✔✔Type 4
✔✔Name the hypersensitivity type: IgM and IgG binding to fixed antigen on enemy cell,
leading to lysis by complement of phagocytosis. - ✔✔Type 2
✔✔Name the hypersensitivity type: Ab-Ag complexes activate complenet and large
immune complex gets stuck in tissues - ✔✔Type 3
