The ASCP MLS (Medical Laboratory Scientist) exam covers multiple areas of laboratory medicine, with immunology being one of the most essential. Understanding the principles of immunology is critical for lab professionals and students, as it forms the foundation of many diagnostic tests, disease interpretations, and therapeutic applications.
This section, Part 35 – Principles of Immunology, includes 80 practice MCQs (3021–3100) in the full series. The focus is to strengthen your understanding of how the immune system functions and how its principles are applied in laboratory testing.
Key Areas Covered
1. Innate and Adaptive Immunity
- Innate immunity as the body’s first line of defense, including skin, mucosal barriers, and phagocytic cells.
- Adaptive immunity with its specificity and memory, involving B and T lymphocytes.
- The importance of distinguishing between cell-mediated and humoral immunity.
2. Cells of the Immune System
- The role of B lymphocytes in antibody production.
- Functions of T helper cells (CD4+), cytotoxic T cells (CD8+), and regulatory T cells.
- Phagocytic action of neutrophils, monocytes, and macrophages.
- Natural killer (NK) cells as nonspecific killers of virus-infected and tumor cells.
3. Antigens and Antibodies
- Antigen recognition and the concept of epitopes.
- Immunoglobulin classes (IgG, IgM, IgA, IgE, IgD) and their structural and functional differences.
- The principle of primary vs. secondary antibody response.
4. Major Histocompatibility Complex (MHC)
- MHC Class I molecules presenting to CD8+ T cells.
- MHC Class II molecules presenting to CD4+ T cells.
- Clinical importance of HLA typing in transplantation and disease associations.
5. Complement System
- Pathways of complement activation: classical, alternative, and lectin.
- Roles in opsonization, chemotaxis, and cell lysis.
- Clinical significance of complement deficiencies.
6. Cytokines and Immune Regulation
- Key cytokines such as IL-1, IL-2, TNF-α, and interferons.
- Their role in inflammation, cell signaling, and immune modulation.
- Importance of cytokines in laboratory testing and therapeutic use.
7. Hypersensitivity and Autoimmunity
- The four types of hypersensitivity reactions.
- Examples such as allergic reactions, hemolytic disease, and immune complex disorders.
- Autoimmune conditions like SLE, rheumatoid arthritis, and Hashimoto thyroiditis, with emphasis on serological markers.
80 MCQs (3021- 3100):
- Which cells are primarily responsible for humoral immunity?
a) T helper cells
b) B lymphocytes
c) Macrophages
d) NK cells - The first line of defense in the immune system is:
a) T cells
b) Antibodies
c) Physical and chemical barriers
d) Complement proteins - Which immunoglobulin is secreted in breast milk and provides mucosal protection?
a) IgG
b) IgM
c) IgA
d) IgE - The major histocompatibility complex (MHC) class I molecules present antigens to:
a) CD8+ T cells
b) CD4+ T cells
c) B cells
d) NK cells - Which immune cells are the first responders to bacterial infection?
a) Basophils
b) Neutrophils
c) Eosinophils
d) T helper cells - The main function of cytotoxic T lymphocytes (CTLs) is to:
a) Activate B cells
b) Kill virus-infected cells
c) Produce antibodies
d) Release histamine - Toll-like receptors (TLRs) are part of:
a) Adaptive immunity
b) Innate immunity
c) Humoral immunity
d) Passive immunity - Which immunoglobulin class is the first produced during a primary immune response?
a) IgG
b) IgM
c) IgA
d) IgE - Passive immunity is best exemplified by:
a) Vaccination
b) Maternal antibodies crossing the placenta
c) Antibody production after infection
d) Memory T cell activation - The complement system can be activated by all except:
a) Classical pathway
b) Alternative pathway
c) Lectin pathway
d) Apoptosis pathway - Natural killer (NK) cells destroy target cells by:
a) Producing antibodies
b) Releasing perforin and granzymes
c) Presenting antigen to T cells
d) Activating complement - Which cytokine is primarily responsible for fever production?
a) IL-1
b) IL-2
c) IL-4
d) IL-10 - Memory cells are generated during:
a) Innate immune response
b) Primary adaptive response
c) Complement activation
d) Passive immunity - Which immunoglobulin mediates allergic reactions?
a) IgG
b) IgA
c) IgE
d) IgM - Which organ is the primary site for T lymphocyte maturation?
a) Bone marrow
b) Spleen
c) Thymus
d) Lymph nodes - The main function of regulatory T cells (Tregs) is to:
a) Enhance antibody production
b) Suppress autoimmunity
c) Promote NK cell activity
d) Activate complement
Answer: b) Suppress autoimmunity - Opsonization enhances phagocytosis by:
a) Inhibiting complement activation
b) Coating antigens with antibodies or complement
c) Destroying T cells
d) Stimulating basophils - Which MHC class presents antigens to CD4+ T cells?
a) Class I
b) Class II
c) Class III
d) Class IV - The process of producing many different antibodies from limited genes is called:
a) Gene splicing
b) Antigenic variation
c) V(D)J recombination
d) Somatic hypermutation - Which immune response is faster upon second exposure to the same antigen?
a) Primary response
b) Secondary response
c) Passive immunity
d) Innate immunity - Which immunoglobulin crosses the placenta?
a) IgM
b) IgA
c) IgG
d) IgE - Antigen-presenting cells (APCs) include all except:
a) Macrophages
b) Dendritic cells
c) B cells
d) Neutrophils - Which enzyme is critical for generating reactive oxygen species in phagocytes?
a) DNA polymerase
b) NADPH oxidase
c) RNA polymerase
d) Catalase - The immunoglobulin with the highest serum concentration is:
a) IgM
b) IgA
c) IgG
d) IgE - Which complement component forms the membrane attack complex (MAC)?
a) C1q
b) C3b
c) C5b-9
d) C4a - Interferons primarily function to:
a) Stimulate antibody production
b) Protect against viral infections
c) Promote phagocytosis of bacteria
d) Neutralize toxins - Which cell type provides a bridge between innate and adaptive immunity?
a) NK cells
b) Dendritic cells
c) Mast cells
d) Neutrophils - Which immunoglobulin is pentameric in structure?
a) IgG
b) IgM
c) IgA
d) IgE - The primary lymphoid organs are:
a) Spleen and lymph nodes
b) Thymus and bone marrow
c) Liver and spleen
d) Tonsils and adenoids - Which process increases antibody affinity after repeated antigen exposure?
a) Antigen presentation
b) Somatic hypermutation
c) Clonal deletion
d) Complement activation - Which type of immunity is present at birth and provides immediate defense?
a) Innate immunity
b) Adaptive immunity
c) Passive immunity
d) Acquired immunity - The process where lymphocytes that strongly recognize self-antigens are eliminated is called:
a) Clonal expansion
b) Clonal deletion
c) Antigen presentation
d) Somatic mutation - Which type of T helper cells are primarily involved in activating macrophages?
a) Th1 cells
b) Th2 cells
c) Th17 cells
d) Treg cells - The antigen-binding site of an antibody is formed by:
a) Constant heavy chains
b) Constant light chains
c) Variable regions of heavy and light chains
d) Fc region - Which cells produce histamine during allergic reactions?
a) B lymphocytes
b) Macrophages
c) Mast cells and basophils
d) NK cells - Which cytokine is the major growth factor for T lymphocytes?
a) IL-1
b) IL-2
c) IL-6
d) TNF-α - Which complement pathway is activated directly by microbial surfaces without antibody involvement?
a) Classical pathway
b) Alternative pathway
c) Lectin pathway
d) Adaptive pathway - Which immune process explains a more rapid antibody response after vaccination booster doses?
a) Clonal deletion
b) Primary immune response
c) Secondary immune response
d) Immune tolerance - Antibodies that prevent microbial attachment to host cells are said to:
a) Neutralize pathogens
b) Opsonize antigens
c) Fix complement
d) Trigger apoptosis - Which immunoglobulin is mainly responsible for defense against parasites?
a) IgA
b) IgE
c) IgM
d) IgG - Which immune organ filters blood and helps clear opsonized microbes?
a) Bone marrow
b) Thymus
c) Spleen
d) Lymph nodes - Which T helper subset is associated with stimulating B cells to produce IgE in allergic responses?
a) Th1
b) Th2
c) Th17
d) Treg - Which molecules are expressed only on antigen-presenting cells (APCs)?
a) MHC class I
b) MHC class II
c) CD8
d) CD19 - Which cells kill virus-infected cells without requiring prior sensitization?
a) Cytotoxic T lymphocytes
b) NK cells
c) Th1 cells
d) Macrophages - Which process generates high-affinity antibodies during B cell maturation?
a) Clonal deletion
b) Affinity maturation
c) Antigen presentation
d) Complement activation - The part of an antigen recognized by an antibody is called:
a) Epitope
b) Paratope
c) Haplotype
d) Allotype - The immune tolerance to self-antigens is established mainly in:
a) Spleen
b) Bone marrow and thymus
c) Lymph nodes
d) Peyer’s patches - Which immunoglobulin appears first in the primary immune response?
a) IgG
b) IgM
c) IgA
d) IgE - Which complement fragment acts as a strong opsonin?
a) C3b
b) C5a
c) C1q
d) C4a - Which immune mechanism protects newborns immediately after birth?
a) IgM production
b) Maternal IgG antibodies
c) NK cell activation
d) Complement activation - The DPT vaccine provides which type of immunity?
a) Active humoral-mediated immunity
b) Passive humoral-mediated immunity
c) Cell-mediated immunity
d) Immediate hypersensitivity - Which group of cells are actively phagocytic?
a) Neutrophils, monocytes, basophils
b) Neutrophils, eosinophils, monocytes
c) Monocytes, lymphocytes, neutrophils
d) Lymphocytes, eosinophils, monocytes - Serum proteins that increase rapidly during infection are known as:
a) Haptens
b) Acute phase reactants
c) Opsonins
d) Chemotaxins - Which acute phase reactant rises the fastest and may increase 100-fold?
a) Alpha-1 antitrypsin
b) Haptoglobin
c) C-reactive protein (CRP)
d) Ceruloplasmin - Acquired immunity is best described by:
a) Nonspecific and nonadaptive mechanisms
b) Internal and external protection
c) Sensitivity with short-term effects
d) Specificity and memory - Skin, lactic acid, mucus, and cilia represent:
a) Natural innate immunity
b) Acquired immunity
c) Adaptive immunity
d) Autoimmunity - Molecules that are antigenic only when bound to a protein carrier are:
a) Opsonins
b) Haptens
c) Adjuvants
d) Allergens - A hapten determinant reacts with:
a) Both T cells and antibody
b) T cells but not antibody
c) Neither T cells nor antibody
d) Antibody but not T cells - Which is true about IgG antibodies?
a) Appear first in primary immune response
b) Larger than IgM
c) Can cross the placenta
d) Detected in saline crossmatches - Cells that develop into plasma cells and secrete immunoglobulins are:
a) Macrophages
b) B lymphocytes
c) T lymphocytes
d) Monocytes - Antibodies are produced by:
a) Killer T cells
b) Bone marrow stem cells directly
c) Mast cells
d) B cells - Polyclonal activation of B cells can:
a) Inhibit antibody production
b) Require T helper cell signals
c) Be caused by suppressor T cells
d) Lead to autoantibody formation - A key feature of macrophages is:
a) Receptors for complement component C3b
b) CD3 expression on the surface
c) Production of antibodies in vitro
d) High rough endoplasmic reticulum activity - Phagocytosis of bacteria by macrophages is enhanced by:
a) Opsonins
b) Antigen alone
c) Haptens
d) Secretory component - Humoral antibodies are secreted by:
a) Macrophages
b) T lymphocytes
c) B lymphocytes
d) Neutrophils - In hybridoma technology, the desired fused cell is:
a) Myeloma–myeloma hybrid
b) Myeloma–lymphocyte hybrid
c) Lymphocyte–lymphocyte hybrid
d) Lymphocyte–granulocyte hybrid - Which test evaluates the function of cellular immunity?
a) Skin testing with common antigens
b) Isohemagglutinin titers
c) Serum immunoelectrophoresis
d) Lymphocyte proliferation assays - T lymphocytes cannot:
a) Help B cells produce antibodies
b) Secrete immunoglobulins
c) Release cytokines
d) Mediate positive skin reactions - T cells do not function as:
a) Cytotoxic cells
b) Helper cells
c) Phagocytic cells
d) Regulatory cells - Nonspecific tumor cell killing is mainly performed by:
a) Cytotoxic T cells
b) Helper T cells
c) Natural killer cells
d) Antibody plus complement - When NK cells encounter a target with MHC class I expression, the result is:
a) Perforins released
b) Granzymes released
c) Inhibition of cytotoxicity
d) Activation of killing - Some genes in MHC class III region encode:
a) Antigens
b) Antibodies
c) Complement proteins
d) Lymphocytes - The primary cell responsible for immune complex tissue injury is:
a) Mast cell
b) Neutrophil
c) Basophil
d) Eosinophil - The main mediators secreted during T cell activation are:
a) Immunoglobulins
b) Complement components
c) Histamine
d) Cytokines - MHC class I molecules include:
a) Complement proteins
b) HLA-A, HLA-B, HLA-C
c) Cytokines
d) HLA-DP, DQ, DR - Receptors for C3b and Fc regions are present on:
a) B lymphocytes
b) Monocytes
c) Both B lymphocytes and monocytes
d) Neither B lymphocytes nor monocytes - T cells with CD8 surface markers carry out:
a) Delayed-type hypersensitivity
b) Regulatory functions
c) Cytotoxic functions
d) Helper functions - In a normal control sample, B lymphocytes represent approximately what percentage of total lymphocytes?
a) 21%
b) 48%
c) 76%
d) 89% - An immunofluorescence test using anti-CD3 identifies:
a) All mature T lymphocytes
b) Helper T cells only
c) Cytotoxic T cells only
d) Regulatory T cells only - Activated CD8 cytotoxic T cells produce which cytokine?
a) Interleukin-13 (IL-13)
b) Interleukin-5 (IL-5)
c) Stromal cell-derived factor-1 (SDF-1)
d) Interferon gamma (IFN-γ)
📌 How to Use This Practice Set
- Answer each question before checking the key.
- Focus on why the correct answer is right and the others are wrong.
- Use this set as timed practice to simulate the real exam environment.
Answer Key
Answer Key:
- b) B lymphocytes
- c) Physical and chemical barriers
- c) IgA
- a) CD8+ T cells
- b) Neutrophils
- b) Kill virus-infected cells
- b) Innate immunity
- b) IgM
- b) Maternal antibodies crossing the placenta
- d) Apoptosis pathway
- b) Releasing perforin and granzymes
- a) IL-1
- b) Primary adaptive response
- c) IgE
- c) Thymus
- b) Suppress autoimmunity
- b) Coating antigens with antibodies or complement
- b) Class II
- c) V(D)J recombination
- b) Secondary response
- c) IgG
- d) Neutrophils
- b) NADPH oxidase
- c) IgG
- c) C5b-9
- b) Protect against viral infections
- b) Dendritic cells
- b) IgM
- b) Thymus and bone marrow
- b) Somatic hypermutation
- a) Innate immunity
- b) Clonal deletion
- a) Th1 cells
- c) Variable regions of heavy and light chains
- c) Mast cells and basophils
- b) IL-2
- b) Alternative pathway
- c) Secondary immune response
- a) Neutralize pathogens
- b) IgE
- c) Spleen
- b) Th2
- b) MHC class II
- b) NK cells
- b) Affinity maturation
- a) Epitope
- b) Bone marrow and thymus
- b) IgM
- a) C3b
- b) Maternal IgG antibodies
- a) Active humoral-mediated immunity
- b) Neutrophils, eosinophils, monocytes
- b) Acute phase reactants
- c) C-reactive protein (CRP)
- d) Specificity and memory
- a) Natural innate immunity
- b) Haptens
- d) Antibody but not T cells
- c) Can cross the placenta
- b) B lymphocytes
- d) B cells
- d) Lead to autoantibody formation
- a) Receptors for complement component C3b
- a) Opsonins
- c) B lymphocytes
- b) Myeloma–lymphocyte hybrid
- d) Lymphocyte proliferation assays
- b) Secrete immunoglobulins
- c) Phagocytic cells
- c) Natural killer cells
- c) Inhibition of cytotoxicity
- c) Complement proteins
- b) Neutrophil
- d) Cytokines
- b) HLA-A, HLA-B, HLA-C
- c) Both B lymphocytes and monocytes
- c) Cytotoxic functions
- a) 21%
- a) All mature T lymphocytes
- d) Interferon gamma (IFN-γ)
Why This Matters for MLS Exam Prep
- Clinical application: Immunology concepts underpin tests like ANA, ELISA, Western blot, complement assays, and flow cytometry.
- Exam relevance: The ASCP MLS exam emphasizes interpretation and application, not just memorization.
- Professional practice: A solid grasp of immunology allows accurate diagnosis of infectious diseases, autoimmune disorders, and immunodeficiencies.
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
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