Immunology USMLE Step 1 Questions
and Answers | Latest Version |
2025/2026 | Correct & Verified
Which cells are primarily responsible for producing antibodies during a primary immune
response?
✔✔ Plasma cells
Which immunoglobulin is most effective at activating the classical complement pathway?
✔✔ IgM
Which immunoglobulin is found in secretions such as saliva, tears, and breast milk?
✔✔ IgA
Which T cell surface protein interacts with MHC class II on antigen-presenting cells?
✔✔ CD4
Which T cell surface protein interacts with MHC class I on infected cells?
✔✔ CD8
1
,Which cell type expresses both CD4 and CD8 during development in the thymus?
✔✔ Double-positive thymocytes
Which cytokine is essential for differentiation of Th1 cells?
✔✔ IL-12
Which cytokine promotes class switching to IgE in B cells?
✔✔ IL-4
Which type of hypersensitivity reaction involves IgE and mast cell degranulation?
✔✔ Type I hypersensitivity
Which immunoglobulin mediates type I hypersensitivity reactions?
✔✔ IgE
Which hypersensitivity reaction is responsible for Goodpasture syndrome?
✔✔ Type II hypersensitivity
2
,Which hypersensitivity reaction is seen in systemic lupus erythematosus?
✔✔ Type III hypersensitivity
Which hypersensitivity type is mediated by T cells rather than antibodies?
✔✔ Type IV hypersensitivity
Which cytokine is most associated with fever and the acute-phase response?
✔✔ IL-1
Which complement component is responsible for opsonization?
✔✔ C3b
Which complement component is responsible for chemotaxis of neutrophils?
✔✔ C5a
Which organ is the site of T cell maturation?
✔✔ Thymus
3
, Which organ is the major site of B cell activation in response to blood-borne antigens?
✔✔ Spleen
Which region of the antibody determines its isotype (IgG, IgA, etc.)?
✔✔ Constant region of the heavy chain
Which region of the antibody determines antigen specificity?
✔✔ Variable region of the Fab fragment
Which major histocompatibility complex presents endogenous antigens to CD8+ T cells?
✔✔ MHC class I
Which major histocompatibility complex presents exogenous antigens to CD4+ T cells?
✔✔ MHC class II
Which molecule is required for T cell activation and functions as a co-stimulatory signal?
✔✔ CD28
4
and Answers | Latest Version |
2025/2026 | Correct & Verified
Which cells are primarily responsible for producing antibodies during a primary immune
response?
✔✔ Plasma cells
Which immunoglobulin is most effective at activating the classical complement pathway?
✔✔ IgM
Which immunoglobulin is found in secretions such as saliva, tears, and breast milk?
✔✔ IgA
Which T cell surface protein interacts with MHC class II on antigen-presenting cells?
✔✔ CD4
Which T cell surface protein interacts with MHC class I on infected cells?
✔✔ CD8
1
,Which cell type expresses both CD4 and CD8 during development in the thymus?
✔✔ Double-positive thymocytes
Which cytokine is essential for differentiation of Th1 cells?
✔✔ IL-12
Which cytokine promotes class switching to IgE in B cells?
✔✔ IL-4
Which type of hypersensitivity reaction involves IgE and mast cell degranulation?
✔✔ Type I hypersensitivity
Which immunoglobulin mediates type I hypersensitivity reactions?
✔✔ IgE
Which hypersensitivity reaction is responsible for Goodpasture syndrome?
✔✔ Type II hypersensitivity
2
,Which hypersensitivity reaction is seen in systemic lupus erythematosus?
✔✔ Type III hypersensitivity
Which hypersensitivity type is mediated by T cells rather than antibodies?
✔✔ Type IV hypersensitivity
Which cytokine is most associated with fever and the acute-phase response?
✔✔ IL-1
Which complement component is responsible for opsonization?
✔✔ C3b
Which complement component is responsible for chemotaxis of neutrophils?
✔✔ C5a
Which organ is the site of T cell maturation?
✔✔ Thymus
3
, Which organ is the major site of B cell activation in response to blood-borne antigens?
✔✔ Spleen
Which region of the antibody determines its isotype (IgG, IgA, etc.)?
✔✔ Constant region of the heavy chain
Which region of the antibody determines antigen specificity?
✔✔ Variable region of the Fab fragment
Which major histocompatibility complex presents endogenous antigens to CD8+ T cells?
✔✔ MHC class I
Which major histocompatibility complex presents exogenous antigens to CD4+ T cells?
✔✔ MHC class II
Which molecule is required for T cell activation and functions as a co-stimulatory signal?
✔✔ CD28
4
